Fix worker documentation around room Admin APIs

Linkify MSC and CVE in the changelog
add backticks to changelog
2025-12-13 01:50:46 +00:00 · 2025-08-21 14:24:40 +01:00 · 2025-08-19 11:01:21 +01:00 · 2025-08-19 11:00:15 +01:00 · 2025-08-19 10:55:42 +01:00 · 2025-08-18 09:28:59 -05:00
57 changed files with 2886 additions and 538 deletions
--- a/.ci/scripts/test_synapse_port_db.sh
+++ b/.ci/scripts/test_synapse_port_db.sh
@@ -61,7 +61,7 @@ poetry run update_synapse_database --database-config .ci/postgres-config-unporte
 echo "+++ Comparing ported schema with unported schema"
 # Ignore the tables that portdb creates. (Should it tidy them up when the porting is completed?)
 psql synapse -c "DROP TABLE port_from_sqlite3;"
-pg_dump --format=plain --schema-only --no-tablespaces --no-acl --no-owner synapse_unported > unported.sql
-pg_dump --format=plain --schema-only --no-tablespaces --no-acl --no-owner synapse          >   ported.sql
+pg_dump --format=plain --schema-only --no-tablespaces --no-acl --no-owner --restrict-key=TESTING synapse_unported > unported.sql
+pg_dump --format=plain --schema-only --no-tablespaces --no-acl --no-owner --restrict-key=TESTING synapse          >   ported.sql
 # By default, `diff` returns zero if there are no changes and nonzero otherwise
-diff -u unported.sql ported.sql | tee schema_diff
+diff -u unported.sql ported.sql | tee schema_diff
--- a/.github/workflows/docker.yml
+++ b/.github/workflows/docker.yml
@@ -31,7 +31,7 @@ jobs:
        uses: docker/setup-buildx-action@e468171a9de216ec08956ac3ada2f0791b6bd435 # v3.11.1

      - name: Checkout repository
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Extract version from pyproject.toml
        # Note: explicitly requesting bash will mean bash is invoked with `-eo pipefail`, see
@@ -95,7 +95,7 @@ jobs:
      - build
    steps:
      - name: Download digests
-        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4.3.0
+        uses: actions/download-artifact@634f93cb2916e3fdff6788551b99b062d0335ce0 # v5.0.0
        with:
          path: ${{ runner.temp }}/digests
          pattern: digests-*
@@ -123,7 +123,7 @@ jobs:
        uses: sigstore/cosign-installer@d58896d6a1865668819e1d91763c7751a165e159 # v3.9.2

      - name: Calculate docker image tag
-        uses: docker/metadata-action@902fa8ec7d6ecbf8d84d538b9b233a880e428804 # v5.7.0
+        uses: docker/metadata-action@c1e51972afc2121e065aed6d45c65596fe445f3f # v5.8.0
        with:
          images: ${{ matrix.repository }}
          flavor: |
--- a/.github/workflows/docs-pr.yaml
+++ b/.github/workflows/docs-pr.yaml
@@ -13,7 +13,7 @@ jobs:
    name: GitHub Pages
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
        with:
          # Fetch all history so that the schema_versions script works.
          fetch-depth: 0
@@ -50,7 +50,7 @@ jobs:
    name: Check links in documentation
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Setup mdbook
        uses: peaceiris/actions-mdbook@ee69d230fe19748b7abf22df32acaa93833fad08 # v2.0.0
--- a/.github/workflows/docs.yaml
+++ b/.github/workflows/docs.yaml
@@ -50,7 +50,7 @@ jobs:
    needs:
      - pre
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
        with:
          # Fetch all history so that the schema_versions script works.
          fetch-depth: 0
--- a/.github/workflows/fix_lint.yaml
+++ b/.github/workflows/fix_lint.yaml
@@ -18,7 +18,7 @@ jobs:

    steps:
      - name: Checkout repository
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
--- a/.github/workflows/latest_deps.yml
+++ b/.github/workflows/latest_deps.yml
@@ -42,7 +42,7 @@ jobs:
    if: needs.check_repo.outputs.should_run_workflow == 'true'
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
        with:
@@ -77,7 +77,7 @@ jobs:
            postgres-version: "14"

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
@@ -152,7 +152,7 @@ jobs:
      BLACKLIST: ${{ matrix.workers && 'synapse-blacklist-with-workers' }}

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
@@ -202,7 +202,7 @@ jobs:

    steps:
      - name: Check out synapse codebase
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
        with:
          path: synapse

@@ -234,7 +234,7 @@ jobs:
    runs-on: ubuntu-latest

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - uses: JasonEtco/create-an-issue@1b14a70e4d8dc185e5cc76d3bec9eab20257b2c5 # v2.9.2
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
--- a/.github/workflows/poetry_lockfile.yaml
+++ b/.github/workflows/poetry_lockfile.yaml
@@ -16,7 +16,7 @@ jobs:
    name: "Check locked dependencies have sdists"
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
        with:
          python-version: '3.x'
--- a/.github/workflows/push_complement_image.yml
+++ b/.github/workflows/push_complement_image.yml
@@ -33,17 +33,17 @@ jobs:
      packages: write
    steps:
      - name: Checkout specific branch (debug build)
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
        if: github.event_name == 'workflow_dispatch'
        with:
          ref: ${{ inputs.branch }}
      - name: Checkout clean copy of develop (scheduled build)
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
        if: github.event_name == 'schedule'
        with:
          ref: develop
      - name: Checkout clean copy of master (on-push)
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
        if: github.event_name == 'push'
        with:
          ref: master
@@ -55,7 +55,7 @@ jobs:
          password: ${{ secrets.GITHUB_TOKEN }}
      - name: Work out labels for complement image
        id: meta
-        uses: docker/metadata-action@902fa8ec7d6ecbf8d84d538b9b233a880e428804 # v5.7.0
+        uses: docker/metadata-action@c1e51972afc2121e065aed6d45c65596fe445f3f # v5.8.0
        with:
          images: ghcr.io/${{ github.repository }}/complement-synapse
          tags: |
--- a/.github/workflows/release-artifacts.yml
+++ b/.github/workflows/release-artifacts.yml
@@ -27,7 +27,7 @@ jobs:
    name: "Calculate list of debian distros"
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
        with:
          python-version: "3.x"
@@ -55,7 +55,7 @@ jobs:

    steps:
      - name: Checkout
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
        with:
          path: src

@@ -66,7 +66,7 @@ jobs:
          install: true

      - name: Set up docker layer caching
-        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
+        uses: actions/cache@0400d5f644dc74513175e3cd8d07132dd4860809 # v4.2.4
        with:
          path: /tmp/.buildx-cache
          key: ${{ runner.os }}-buildx-${{ github.sha }}
@@ -132,7 +132,7 @@ jobs:
            os: "ubuntu-24.04-arm"

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
        with:
@@ -165,7 +165,7 @@ jobs:
    if: ${{ !startsWith(github.ref, 'refs/pull/') }}

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
        with:
          python-version: "3.10"
@@ -191,7 +191,7 @@ jobs:
    runs-on: ubuntu-latest
    steps:
      - name: Download all workflow run artifacts
-        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4.3.0
+        uses: actions/download-artifact@634f93cb2916e3fdff6788551b99b062d0335ce0 # v5.0.0
      - name: Build a tarball for the debs
        # We need to merge all the debs uploads into one folder, then compress
        # that.
--- a/.github/workflows/schema.yaml
+++ b/.github/workflows/schema.yaml
@@ -14,7 +14,7 @@ jobs:
    name: Ensure Synapse config schema is valid
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
        with:
          python-version: "3.x"
@@ -40,7 +40,7 @@ jobs:
    name: Ensure generated documentation is up-to-date
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
        with:
          python-version: "3.x"
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -86,7 +86,7 @@ jobs:
    if: ${{ needs.changes.outputs.linting == 'true' }}

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
        with:
@@ -106,7 +106,7 @@ jobs:
    if: ${{ needs.changes.outputs.linting == 'true' }}

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
        with:
          python-version: "3.x"
@@ -116,7 +116,7 @@ jobs:
  check-lockfile:
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
        with:
          python-version: "3.x"
@@ -129,7 +129,7 @@ jobs:

    steps:
      - name: Checkout repository
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Setup Poetry
        uses: matrix-org/setup-python-poetry@5bbf6603c5c930615ec8a29f1b5d7d258d905aa4 # v2.0.0
@@ -151,7 +151,7 @@ jobs:

    steps:
      - name: Checkout repository
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
@@ -174,7 +174,7 @@ jobs:
      # Cribbed from
      # https://github.com/AustinScola/mypy-cache-github-action/blob/85ea4f2972abed39b33bd02c36e341b28ca59213/src/restore.ts#L10-L17
      - name: Restore/persist mypy's cache
-        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
+        uses: actions/cache@0400d5f644dc74513175e3cd8d07132dd4860809 # v4.2.4
        with:
          path: |
            .mypy_cache
@@ -187,7 +187,7 @@ jobs:
  lint-crlf:
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - name: Check line endings
        run: scripts-dev/check_line_terminators.sh

@@ -195,7 +195,7 @@ jobs:
    if: ${{ (github.base_ref == 'develop'  || contains(github.base_ref, 'release-')) && github.actor != 'dependabot[bot]' }}
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
        with:
          ref: ${{ github.event.pull_request.head.sha }}
          fetch-depth: 0
@@ -213,7 +213,7 @@ jobs:
    if: ${{ needs.changes.outputs.linting == 'true' }}

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
        with:
          ref: ${{ github.event.pull_request.head.sha }}
      - name: Install Rust
@@ -233,7 +233,7 @@ jobs:
    if: ${{ needs.changes.outputs.rust == 'true' }}

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
@@ -252,7 +252,7 @@ jobs:
    if: ${{ needs.changes.outputs.rust == 'true' }}

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
@@ -270,7 +270,7 @@ jobs:

    steps:
      - name: Checkout repository
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
@@ -306,7 +306,7 @@ jobs:
    if: ${{ needs.changes.outputs.rust == 'true' }}

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
@@ -326,7 +326,7 @@ jobs:
    needs: changes
    if: ${{ needs.changes.outputs.linting_readme == 'true' }}
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
        with:
          python-version: "3.x"
@@ -376,7 +376,7 @@ jobs:
    needs: linting-done
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
        with:
          python-version: "3.x"
@@ -397,7 +397,7 @@ jobs:
        job:  ${{ fromJson(needs.calculate-test-jobs.outputs.trial_test_matrix) }}

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - run: sudo apt-get -qq install xmlsec1
      - name: Set up PostgreSQL ${{ matrix.job.postgres-version }}
        if: ${{ matrix.job.postgres-version }}
@@ -453,7 +453,7 @@ jobs:
      - changes
    runs-on: ubuntu-22.04
    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
@@ -518,7 +518,7 @@ jobs:
        extras: ["all"]

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      # Install libs necessary for PyPy to build binary wheels for dependencies
      - run: sudo apt-get -qq install xmlsec1 libxml2-dev libxslt-dev
      - uses: matrix-org/setup-python-poetry@5bbf6603c5c930615ec8a29f1b5d7d258d905aa4 # v2.0.0
@@ -568,7 +568,7 @@ jobs:
        job: ${{ fromJson(needs.calculate-test-jobs.outputs.sytest_test_matrix) }}

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - name: Prepare test blacklist
        run: cat sytest-blacklist .ci/worker-blacklist > synapse-blacklist-with-workers

@@ -615,7 +615,7 @@ jobs:
          --health-retries 5

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - run: sudo apt-get -qq install xmlsec1 postgresql-client
      - uses: matrix-org/setup-python-poetry@5bbf6603c5c930615ec8a29f1b5d7d258d905aa4 # v2.0.0
        with:
@@ -659,7 +659,7 @@ jobs:
          --health-retries 5

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - name: Add PostgreSQL apt repository
        # We need a version of pg_dump that can handle the version of
        # PostgreSQL being tested against. The Ubuntu package repository lags
@@ -714,7 +714,7 @@ jobs:

    steps:
      - name: Checkout synapse codebase
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
        with:
          path: synapse

@@ -750,7 +750,7 @@ jobs:
      - changes

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
@@ -770,7 +770,7 @@ jobs:
      - changes

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
--- a/.github/workflows/triage_labelled.yml
+++ b/.github/workflows/triage_labelled.yml
@@ -11,7 +11,7 @@ jobs:
    if: >
      contains(github.event.issue.labels.*.name, 'X-Needs-Info')
    steps:
-      - uses: actions/add-to-project@5b1a254a3546aef88e0a7724a77a623fa2e47c36 # main (v1.0.2 + 10 commits)
+      - uses: actions/add-to-project@c0c5949b017d0d4a39f7ba888255881bdac2a823 # v1.0.2
        id: add_project
        with:
          project-url: "https://github.com/orgs/matrix-org/projects/67"
--- a/.github/workflows/twisted_trunk.yml
+++ b/.github/workflows/twisted_trunk.yml
@@ -43,7 +43,7 @@ jobs:
    runs-on: ubuntu-latest

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
@@ -70,7 +70,7 @@ jobs:
    runs-on: ubuntu-latest

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - run: sudo apt-get -qq install xmlsec1

      - name: Install Rust
@@ -117,7 +117,7 @@ jobs:
        - ${{ github.workspace }}:/src

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0

      - name: Install Rust
        uses: dtolnay/rust-toolchain@b3b07ba8b418998c39fb20f53e8b695cdcc8de1b # master
@@ -175,7 +175,7 @@ jobs:

    steps:
      - name: Run actions/checkout@v4 for synapse
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
        with:
          path: synapse

@@ -217,7 +217,7 @@ jobs:
    runs-on: ubuntu-latest

    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
      - uses: JasonEtco/create-an-issue@1b14a70e4d8dc185e5cc76d3bec9eab20257b2c5 # v2.9.2
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,83 @@
+# Synapse 1.137.0rc1 (2025-08-19)
+
+### Bugfixes
+
+- Fix a bug which could corrupt auth chains making it impossible to perform state resolution. ([\#18746](https://github.com/element-hq/synapse/issues/18746))
+- Fix error message in `register_new_matrix_user` utility script for empty `registration_shared_secret`. ([\#18780](https://github.com/element-hq/synapse/issues/18780))
+- Allow enabling [MSC4108](https://github.com/matrix-org/matrix-spec-proposals/pull/4108) when the stable Matrix Authentication Service integration is enabled. ([\#18832](https://github.com/element-hq/synapse/issues/18832))
+
+### Improved Documentation
+
+- Include IPv6 networks in `denied-peer-ips` of coturn setup. Contributed by @litetex. ([\#18781](https://github.com/element-hq/synapse/issues/18781))
+
+### Internal Changes
+
+- Update tests to ensure all database tables are emptied when purging a room. ([\#18794](https://github.com/element-hq/synapse/issues/18794))
+- Instrument the `encode_response` part of Sliding Sync requests for more complete traces in Jaeger. ([\#18815](https://github.com/element-hq/synapse/issues/18815))
+- Tag Sliding Sync traces when we `wait_for_events`. ([\#18816](https://github.com/element-hq/synapse/issues/18816))
+- Fix `portdb` CI by hardcoding the new `pg_dump` restrict key that was added due to [CVE-2025-8714](https://nvd.nist.gov/vuln/detail/cve-2025-8714). ([\#18824](https://github.com/element-hq/synapse/issues/18824))
+
+
+
+### Updates to locked dependencies
+
+* Bump actions/add-to-project from 5b1a254a3546aef88e0a7724a77a623fa2e47c36 to 0c37450c4be3b6a7582b2fb013c9ebfd9c8e9300. ([\#18557](https://github.com/element-hq/synapse/issues/18557))
+* Bump actions/cache from 4.2.3 to 4.2.4. ([\#18799](https://github.com/element-hq/synapse/issues/18799))
+* Bump actions/checkout from 4.2.2 to 4.3.0. ([\#18800](https://github.com/element-hq/synapse/issues/18800))
+* Bump actions/download-artifact from 4.3.0 to 5.0.0. ([\#18801](https://github.com/element-hq/synapse/issues/18801))
+* Bump docker/metadata-action from 5.7.0 to 5.8.0. ([\#18773](https://github.com/element-hq/synapse/issues/18773))
+* Bump mypy from 1.16.1 to 1.17.1. ([\#18775](https://github.com/element-hq/synapse/issues/18775))
+* Bump phonenumbers from 9.0.10 to 9.0.11. ([\#18797](https://github.com/element-hq/synapse/issues/18797))
+* Bump pygithub from 2.6.1 to 2.7.0. ([\#18779](https://github.com/element-hq/synapse/issues/18779))
+* Bump serde_json from 1.0.141 to 1.0.142. ([\#18776](https://github.com/element-hq/synapse/issues/18776))
+* Bump slab from 0.4.10 to 0.4.11. ([\#18809](https://github.com/element-hq/synapse/issues/18809))
+* Bump tokio from 1.47.0 to 1.47.1. ([\#18774](https://github.com/element-hq/synapse/issues/18774))
+* Bump types-pyyaml from 6.0.12.20250516 to 6.0.12.20250809. ([\#18798](https://github.com/element-hq/synapse/issues/18798))
+* Bump types-setuptools from 80.9.0.20250529 to 80.9.0.20250809. ([\#18796](https://github.com/element-hq/synapse/issues/18796))
+
+# Synapse 1.136.0 (2025-08-12)
+
+Note: This release includes the security fixes from `1.135.2` and `1.136.0rc2`, detailed below.
+
+### Bugfixes
+
+- Fix bug introduced in 1.135.2 and 1.136.0rc2 where the [Make Room Admin API](https://element-hq.github.io/synapse/latest/admin_api/rooms.html#make-room-admin-api) would not treat a room v12's creator power level as the highest in room. ([\#18805](https://github.com/element-hq/synapse/issues/18805))
+
+
+# Synapse 1.135.2 (2025-08-11)
+
+This is the Synapse portion of the [Matrix coordinated security release](https://matrix.org/blog/2025/07/security-predisclosure/). This release includes support for [room version](https://spec.matrix.org/v1.15/rooms/) 12 which fixes a number of security vulnerabilities, including [CVE-2025-49090](https://www.cve.org/CVERecord?id=CVE-2025-49090).
+
+The default room version is not changed. Not all clients will support room version 12 immediately, and not all users will be using the latest version of their clients. Large, public rooms are advised to wait a few weeks before upgrading to room version 12 to allow users throughout the Matrix ecosystem to update their clients.
+
+Note: release 1.135.1 was skipped due to issues discovered during the release process.
+
+Two patched Synapse releases are now available:
+
+* `1.135.2`: stable release comprised of `1.135.0` + security patches
+    * Upgrade to this release **if you are currently running 1.135.0 or below**.
+* `1.136.0rc2`: unstable release candidate comprised of `1.136.0rc1` + security patches.
+    * Upgrade to this release **only if you are on 1.136.0rc1**.
+
+### Bugfixes
+
+- Fix invalidation of storage cache that was broken in 1.135.0. ([\#18786](https://github.com/element-hq/synapse/issues/18786))
+
+### Internal Changes
+
+- Add a parameter to `upgrade_rooms(..)` to allow auto join local users. ([\#82](https://github.com/element-hq/synapse/issues/82))
+- Speed up upgrading a room with large numbers of banned users. ([\#18574](https://github.com/element-hq/synapse/issues/18574))
+
+
+# Synapse 1.136.0rc2 (2025-08-11)
+
+- Update MSC4293 redaction logic for room v12. ([\#80](https://github.com/element-hq/synapse/issues/80))
+
+### Internal Changes
+
+- Add a parameter to `upgrade_rooms(..)` to allow auto join local users. ([\#83](https://github.com/element-hq/synapse/issues/83))
+
+
 # Synapse 1.136.0rc1 (2025-08-05)

 Please check [the relevant section in the upgrade notes](https://github.com/element-hq/synapse/blob/develop/docs/upgrade.md#upgrading-to-v11360) as this release contains changes to MAS support, metrics labels and the module API which may require your attention when upgrading.
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1270,9 +1270,9 @@ dependencies = [

 [[package]]
 name = "serde_json"
-version = "1.0.141"
+version = "1.0.142"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "30b9eff21ebe718216c6ec64e1d9ac57087aad11efc64e32002bce4a0d4c03d3"
+checksum = "030fedb782600dcbd6f02d479bf0d817ac3bb40d644745b769d6a96bc3afc5a7"
 dependencies = [
 "itoa",
 "memchr",
@@ -1322,9 +1322,9 @@ checksum = "0fda2ff0d084019ba4d7c6f371c95d8fd75ce3524c3cb8fb653a3023f6323e64"

 [[package]]
 name = "slab"
-version = "0.4.10"
+version = "0.4.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "04dc19736151f35336d325007ac991178d504a119863a2fcb3758cdb5e52c50d"
+checksum = "7a2ae44ef20feb57a68b23d846850f861394c2e02dc425a50098ae8c90267589"

 [[package]]
 name = "smallvec"
@@ -1478,9 +1478,9 @@ checksum = "1f3ccbac311fea05f86f61904b462b55fb3df8837a366dfc601a0161d0532f20"

 [[package]]
 name = "tokio"
-version = "1.47.0"
+version = "1.47.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "43864ed400b6043a4757a25c7a64a8efde741aed79a056a2fb348a406701bb35"
+checksum = "89e49afdadebb872d3145a5638b59eb0691ea23e46ca484037cfab3b76b95038"
 dependencies = [
 "backtrace",
 "bytes",
--- a/changelog.d/18853.doc.md
+++ b/changelog.d/18853.doc.md
@@ -0,0 +1 @@
+Fix worker documentation incorrectly indicating all room Admin API requests were capable of being handled by workers.
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,9 +1,39 @@
+matrix-synapse-py3 (1.137.0~rc1) stable; urgency=medium
+
+  * New Synapse release 1.137.0rc1.
+
+ -- Synapse Packaging team <packages@matrix.org>  Tue, 19 Aug 2025 10:55:22 +0100
+
+matrix-synapse-py3 (1.136.0) stable; urgency=medium
+
+  * New Synapse release 1.136.0.
+
+ -- Synapse Packaging team <packages@matrix.org>  Tue, 12 Aug 2025 13:18:03 +0100
+
+matrix-synapse-py3 (1.136.0~rc2) stable; urgency=medium
+
+  * New Synapse release 1.136.0rc2.
+
+ -- Synapse Packaging team <packages@matrix.org>  Mon, 11 Aug 2025 12:18:52 -0600
+
 matrix-synapse-py3 (1.136.0~rc1) stable; urgency=medium

  * New Synapse release 1.136.0rc1.

 -- Synapse Packaging team <packages@matrix.org>  Tue, 05 Aug 2025 08:13:30 -0600

+matrix-synapse-py3 (1.135.2) stable; urgency=medium
+
+  * New Synapse release 1.135.2.
+
+ -- Synapse Packaging team <packages@matrix.org>  Mon, 11 Aug 2025 11:52:01 -0600
+
+matrix-synapse-py3 (1.135.1) stable; urgency=medium
+
+  * New Synapse release 1.135.1.
+
+ -- Synapse Packaging team <packages@matrix.org>  Mon, 11 Aug 2025 11:13:15 -0600
+
 matrix-synapse-py3 (1.135.0) stable; urgency=medium

  * New Synapse release 1.135.0.
--- a/docs/setup/turn/coturn.md
+++ b/docs/setup/turn/coturn.md
@@ -88,7 +88,8 @@ This will install and start a systemd service called `coturn`.
    denied-peer-ip=172.16.0.0-172.31.255.255

    # recommended additional local peers to block, to mitigate external access to internal services.
-    # https://www.rtcsec.com/article/slack-webrtc-turn-compromise-and-bug-bounty/#how-to-fix-an-open-turn-relay-to-address-this-vulnerability
+    # https://www.enablesecurity.com/blog/slack-webrtc-turn-compromise-and-bug-bounty/#how-to-fix-an-open-turn-relay-to-address-this-vulnerability
+    # https://www.enablesecurity.com/blog/cve-2020-26262-bypass-of-coturns-access-control-protection/#further-concerns-what-else
    no-multicast-peers
    denied-peer-ip=0.0.0.0-0.255.255.255
    denied-peer-ip=100.64.0.0-100.127.255.255
@@ -101,6 +102,14 @@ This will install and start a systemd service called `coturn`.
    denied-peer-ip=198.51.100.0-198.51.100.255
    denied-peer-ip=203.0.113.0-203.0.113.255
    denied-peer-ip=240.0.0.0-255.255.255.255
+    denied-peer-ip=::1
+    denied-peer-ip=64:ff9b::-64:ff9b::ffff:ffff
+    denied-peer-ip=::ffff:0.0.0.0-::ffff:255.255.255.255
+    denied-peer-ip=100::-100::ffff:ffff:ffff:ffff
+    denied-peer-ip=2001::-2001:1ff:ffff:ffff:ffff:ffff:ffff:ffff
+    denied-peer-ip=2002::-2002:ffff:ffff:ffff:ffff:ffff:ffff:ffff
+    denied-peer-ip=fc00::-fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
+    denied-peer-ip=fe80::-febf:ffff:ffff:ffff:ffff:ffff:ffff:ffff

    # special case the turn server itself so that client->TURN->TURN->client flows work
    # this should be one of the turn server's listening IPs
--- a/docs/usage/configuration/config_documentation.md
+++ b/docs/usage/configuration/config_documentation.md
@@ -4174,7 +4174,7 @@ The default power levels for each preset are:
 "m.room.history_visibility": 100
 "m.room.canonical_alias": 50
 "m.room.avatar": 50
-"m.room.tombstone": 100
+"m.room.tombstone": 100 (150 if MSC4289 is used)
 "m.room.server_acl": 100
 "m.room.encryption": 100
 ```
--- a/docs/workers.md
+++ b/docs/workers.md
@@ -252,7 +252,7 @@ information.
    ^/_matrix/client/(api/v1|r0|v3|unstable)/directory/room/.*$
    ^/_matrix/client/(r0|v3|unstable)/capabilities$
    ^/_matrix/client/(r0|v3|unstable)/notifications$
-    ^/_synapse/admin/v1/rooms/
+    ^/_synapse/admin/v1/rooms/[^/]+$

    # Encryption requests
    ^/_matrix/client/(r0|v3|unstable)/keys/query$
--- a/poetry.lock
+++ b/poetry.lock
@@ -441,24 +441,6 @@ files = [
    {file = "defusedxml-0.7.1.tar.gz", hash = "sha256:1bb3032db185915b62d7c6209c5a8792be6a32ab2fedacc84e01b52c51aa3e69"},
 ]

-[[package]]
-name = "deprecated"
-version = "1.2.13"
-description = "Python @deprecated decorator to deprecate old python classes, functions or methods."
-optional = false
-python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
-groups = ["dev"]
-files = [
-    {file = "Deprecated-1.2.13-py2.py3-none-any.whl", hash = "sha256:64756e3e14c8c5eea9795d93c524551432a0be75629f8f29e67ab8caf076c76d"},
-    {file = "Deprecated-1.2.13.tar.gz", hash = "sha256:43ac5335da90c31c24ba028af536a91d41d53f9e6901ddb021bcc572ce44e38d"},
-]
-
-[package.dependencies]
-wrapt = ">=1.10,<2"
-
-[package.extras]
-dev = ["PyTest (<5) ; python_version < \"3.6\"", "PyTest ; python_version >= \"3.6\"", "PyTest-Cov (<2.6) ; python_version < \"3.6\"", "PyTest-Cov ; python_version >= \"3.6\"", "bump2version (<1)", "configparser (<5) ; python_version < \"3\"", "importlib-metadata (<3) ; python_version < \"3\"", "importlib-resources (<4) ; python_version < \"3\"", "sphinx (<2)", "sphinxcontrib-websupport (<2) ; python_version < \"3\"", "tox", "zipp (<2) ; python_version < \"3\""]
-
 [[package]]
 name = "docutils"
 version = "0.19"
@@ -1387,44 +1369,50 @@ docs = ["sphinx (>=8,<9)", "sphinx-autobuild"]

 [[package]]
 name = "mypy"
-version = "1.16.1"
+version = "1.17.1"
 description = "Optional static typing for Python"
 optional = false
 python-versions = ">=3.9"
 groups = ["dev"]
 files = [
-    {file = "mypy-1.16.1-cp310-cp310-macosx_10_9_x86_64.whl", hash = "sha256:b4f0fed1022a63c6fec38f28b7fc77fca47fd490445c69d0a66266c59dd0b88a"},
-    {file = "mypy-1.16.1-cp310-cp310-macosx_11_0_arm64.whl", hash = "sha256:86042bbf9f5a05ea000d3203cf87aa9d0ccf9a01f73f71c58979eb9249f46d72"},
-    {file = "mypy-1.16.1-cp310-cp310-manylinux_2_17_aarch64.manylinux2014_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:ea7469ee5902c95542bea7ee545f7006508c65c8c54b06dc2c92676ce526f3ea"},
-    {file = "mypy-1.16.1-cp310-cp310-manylinux_2_17_x86_64.manylinux2014_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:352025753ef6a83cb9e7f2427319bb7875d1fdda8439d1e23de12ab164179574"},
-    {file = "mypy-1.16.1-cp310-cp310-musllinux_1_2_x86_64.whl", hash = "sha256:ff9fa5b16e4c1364eb89a4d16bcda9987f05d39604e1e6c35378a2987c1aac2d"},
-    {file = "mypy-1.16.1-cp310-cp310-win_amd64.whl", hash = "sha256:1256688e284632382f8f3b9e2123df7d279f603c561f099758e66dd6ed4e8bd6"},
-    {file = "mypy-1.16.1-cp311-cp311-macosx_10_9_x86_64.whl", hash = "sha256:472e4e4c100062488ec643f6162dd0d5208e33e2f34544e1fc931372e806c0cc"},
-    {file = "mypy-1.16.1-cp311-cp311-macosx_11_0_arm64.whl", hash = "sha256:ea16e2a7d2714277e349e24d19a782a663a34ed60864006e8585db08f8ad1782"},
-    {file = "mypy-1.16.1-cp311-cp311-manylinux_2_17_aarch64.manylinux2014_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:08e850ea22adc4d8a4014651575567b0318ede51e8e9fe7a68f25391af699507"},
-    {file = "mypy-1.16.1-cp311-cp311-manylinux_2_17_x86_64.manylinux2014_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:22d76a63a42619bfb90122889b903519149879ddbf2ba4251834727944c8baca"},
-    {file = "mypy-1.16.1-cp311-cp311-musllinux_1_2_x86_64.whl", hash = "sha256:2c7ce0662b6b9dc8f4ed86eb7a5d505ee3298c04b40ec13b30e572c0e5ae17c4"},
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-
 [[package]]
 name = "xmlschema"
 version = "2.4.0"
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -101,7 +101,7 @@ module-name = "synapse.synapse_rust"

 [tool.poetry]
 name = "matrix-synapse"
-version = "1.136.0rc1"
+version = "1.137.0rc1"
 description = "Homeserver for the Matrix decentralised comms protocol"
 authors = ["Matrix.org Team and Contributors <packages@matrix.org>"]
 license = "AGPL-3.0-or-later"
--- a/schema/synapse-config.schema.yaml
+++ b/schema/synapse-config.schema.yaml
@@ -1,5 +1,5 @@
 $schema: https://element-hq.github.io/synapse/latest/schema/v1/meta.schema.json
-$id: https://element-hq.github.io/synapse/schema/synapse/v1.136/synapse-config.schema.json
+$id: https://element-hq.github.io/synapse/schema/synapse/v1.137/synapse-config.schema.json
 type: object
 properties:
  modules:
@@ -5184,7 +5184,7 @@ properties:

      "m.room.avatar": 50

-      "m.room.tombstone": 100
+      "m.room.tombstone": 100 (150 if MSC4289 is used)

      "m.room.server_acl": 100

--- a/synapse/_scripts/register_new_matrix_user.py
+++ b/synapse/_scripts/register_new_matrix_user.py
@@ -30,6 +30,7 @@ from typing import Any, Callable, Dict, Optional

 import requests
 import yaml
+from typing_extensions import Never

 _CONFLICTING_SHARED_SECRET_OPTS_ERROR = """\
 Conflicting options 'registration_shared_secret' and 'registration_shared_secret_path'
@@ -40,6 +41,10 @@ _NO_SHARED_SECRET_OPTS_ERROR = """\
 No 'registration_shared_secret' or 'registration_shared_secret_path' defined in config.
 """

+_EMPTY_SHARED_SECRET_PATH_OPTS_ERROR = """\
+The secret given via `registration_shared_secret_path` must not be empty.
+"""
+
 _DEFAULT_SERVER_URL = "http://localhost:8008"


@@ -170,6 +175,12 @@ def register_new_user(
    )


+def bail(err_msg: str) -> Never:
+    """Prints the given message to stderr and exits."""
+    print(err_msg, file=sys.stderr)
+    sys.exit(1)
+
+
 def main() -> None:
    logging.captureWarnings(True)

@@ -262,15 +273,20 @@ def main() -> None:
        assert config is not None

        secret = config.get("registration_shared_secret")
+        if not isinstance(secret, (str, type(None))):
+            bail("registration_shared_secret is not a string.")
        secret_file = config.get("registration_shared_secret_path")
-        if secret_file:
-            if secret:
-                print(_CONFLICTING_SHARED_SECRET_OPTS_ERROR, file=sys.stderr)
-                sys.exit(1)
+        if not isinstance(secret_file, (str, type(None))):
+            bail("registration_shared_secret_path is not a string.")
+
+        if not secret and not secret_file:
+            bail(_NO_SHARED_SECRET_OPTS_ERROR)
+        elif secret and secret_file:
+            bail(_CONFLICTING_SHARED_SECRET_OPTS_ERROR)
+        elif not secret and secret_file:
            secret = _read_file(secret_file, "registration_shared_secret_path").strip()
-        if not secret:
-            print(_NO_SHARED_SECRET_OPTS_ERROR, file=sys.stderr)
-            sys.exit(1)
+            if not secret:
+                bail(_EMPTY_SHARED_SECRET_PATH_OPTS_ERROR)

    if args.password_file:
        password = _read_file(args.password_file, "password-file").strip()
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -46,6 +46,9 @@ MAX_USERID_LENGTH = 255
 # Constant value used for the pseudo-thread which is the main timeline.
 MAIN_TIMELINE: Final = "main"

+# MAX_INT + 1, so it always trumps any PL in canonical JSON.
+CREATOR_POWER_LEVEL = 2**53
+

 class Membership:
    """Represents the membership states of a user in a room."""
@@ -235,6 +238,8 @@ class EventContentFields:
    #
    # This is deprecated in MSC2175.
    ROOM_CREATOR: Final = "creator"
+    # MSC4289
+    ADDITIONAL_CREATORS: Final = "additional_creators"

    # The version of the room for `m.room.create` events.
    ROOM_VERSION: Final = "room_version"
--- a/synapse/api/room_versions.py
+++ b/synapse/api/room_versions.py
@@ -36,12 +36,14 @@ class EventFormatVersions:
    ROOM_V1_V2 = 1  # $id:server event id format: used for room v1 and v2
    ROOM_V3 = 2  # MSC1659-style $hash event id format: used for room v3
    ROOM_V4_PLUS = 3  # MSC1884-style $hash format: introduced for room v4
+    ROOM_V11_HYDRA_PLUS = 4  # MSC4291 room IDs as hashes: introduced for room HydraV11


 KNOWN_EVENT_FORMAT_VERSIONS = {
    EventFormatVersions.ROOM_V1_V2,
    EventFormatVersions.ROOM_V3,
    EventFormatVersions.ROOM_V4_PLUS,
+    EventFormatVersions.ROOM_V11_HYDRA_PLUS,
 }


@@ -50,6 +52,7 @@ class StateResolutionVersions:

    V1 = 1  # room v1 state res
    V2 = 2  # MSC1442 state res: room v2 and later
+    V2_1 = 3  # MSC4297 state res


 class RoomDisposition:
@@ -109,6 +112,10 @@ class RoomVersion:
    msc3931_push_features: Tuple[str, ...]  # values from PushRuleRoomFlag
    # MSC3757: Restricting who can overwrite a state event
    msc3757_enabled: bool
+    # MSC4289: Creator power enabled
+    msc4289_creator_power_enabled: bool
+    # MSC4291: Room IDs as hashes of the create event
+    msc4291_room_ids_as_hashes: bool


 class RoomVersions:
@@ -131,6 +138,8 @@ class RoomVersions:
        enforce_int_power_levels=False,
        msc3931_push_features=(),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    V2 = RoomVersion(
        "2",
@@ -151,6 +160,8 @@ class RoomVersions:
        enforce_int_power_levels=False,
        msc3931_push_features=(),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    V3 = RoomVersion(
        "3",
@@ -171,6 +182,8 @@ class RoomVersions:
        enforce_int_power_levels=False,
        msc3931_push_features=(),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    V4 = RoomVersion(
        "4",
@@ -191,6 +204,8 @@ class RoomVersions:
        enforce_int_power_levels=False,
        msc3931_push_features=(),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    V5 = RoomVersion(
        "5",
@@ -211,6 +226,8 @@ class RoomVersions:
        enforce_int_power_levels=False,
        msc3931_push_features=(),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    V6 = RoomVersion(
        "6",
@@ -231,6 +248,8 @@ class RoomVersions:
        enforce_int_power_levels=False,
        msc3931_push_features=(),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    V7 = RoomVersion(
        "7",
@@ -251,6 +270,8 @@ class RoomVersions:
        enforce_int_power_levels=False,
        msc3931_push_features=(),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    V8 = RoomVersion(
        "8",
@@ -271,6 +292,8 @@ class RoomVersions:
        enforce_int_power_levels=False,
        msc3931_push_features=(),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    V9 = RoomVersion(
        "9",
@@ -291,6 +314,8 @@ class RoomVersions:
        enforce_int_power_levels=False,
        msc3931_push_features=(),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    V10 = RoomVersion(
        "10",
@@ -311,6 +336,8 @@ class RoomVersions:
        enforce_int_power_levels=True,
        msc3931_push_features=(),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    MSC1767v10 = RoomVersion(
        # MSC1767 (Extensible Events) based on room version "10"
@@ -332,6 +359,8 @@ class RoomVersions:
        enforce_int_power_levels=True,
        msc3931_push_features=(PushRuleRoomFlag.EXTENSIBLE_EVENTS,),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    MSC3757v10 = RoomVersion(
        # MSC3757 (Restricting who can overwrite a state event) based on room version "10"
@@ -353,6 +382,8 @@ class RoomVersions:
        enforce_int_power_levels=True,
        msc3931_push_features=(),
        msc3757_enabled=True,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    V11 = RoomVersion(
        "11",
@@ -373,6 +404,8 @@ class RoomVersions:
        enforce_int_power_levels=True,
        msc3931_push_features=(),
        msc3757_enabled=False,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
    )
    MSC3757v11 = RoomVersion(
        # MSC3757 (Restricting who can overwrite a state event) based on room version "11"
@@ -394,6 +427,52 @@ class RoomVersions:
        enforce_int_power_levels=True,
        msc3931_push_features=(),
        msc3757_enabled=True,
+        msc4289_creator_power_enabled=False,
+        msc4291_room_ids_as_hashes=False,
+    )
+    HydraV11 = RoomVersion(
+        "org.matrix.hydra.11",
+        RoomDisposition.UNSTABLE,
+        EventFormatVersions.ROOM_V11_HYDRA_PLUS,
+        StateResolutionVersions.V2_1,  # Changed from v11
+        enforce_key_validity=True,
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        implicit_room_creator=True,  # Used by MSC3820
+        updated_redaction_rules=True,  # Used by MSC3820
+        restricted_join_rule=True,
+        restricted_join_rule_fix=True,
+        knock_join_rule=True,
+        msc3389_relation_redactions=False,
+        knock_restricted_join_rule=True,
+        enforce_int_power_levels=True,
+        msc3931_push_features=(),
+        msc3757_enabled=False,
+        msc4289_creator_power_enabled=True,  # Changed from v11
+        msc4291_room_ids_as_hashes=True,  # Changed from v11
+    )
+    V12 = RoomVersion(
+        "12",
+        RoomDisposition.STABLE,
+        EventFormatVersions.ROOM_V11_HYDRA_PLUS,
+        StateResolutionVersions.V2_1,  # Changed from v11
+        enforce_key_validity=True,
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        implicit_room_creator=True,  # Used by MSC3820
+        updated_redaction_rules=True,  # Used by MSC3820
+        restricted_join_rule=True,
+        restricted_join_rule_fix=True,
+        knock_join_rule=True,
+        msc3389_relation_redactions=False,
+        knock_restricted_join_rule=True,
+        enforce_int_power_levels=True,
+        msc3931_push_features=(),
+        msc3757_enabled=False,
+        msc4289_creator_power_enabled=True,  # Changed from v11
+        msc4291_room_ids_as_hashes=True,  # Changed from v11
    )


@@ -411,8 +490,10 @@ KNOWN_ROOM_VERSIONS: Dict[str, RoomVersion] = {
        RoomVersions.V9,
        RoomVersions.V10,
        RoomVersions.V11,
+        RoomVersions.V12,
        RoomVersions.MSC3757v10,
        RoomVersions.MSC3757v11,
+        RoomVersions.HydraV11,
    )
 }

--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -535,11 +535,15 @@ class ExperimentalConfig(Config):
            "msc4108_delegation_endpoint", None
        )

+        auth_delegated = self.msc3861.enabled or (
+            config.get("matrix_authentication_service") or {}
+        ).get("enabled", False)
+
        if (
            self.msc4108_enabled or self.msc4108_delegation_endpoint is not None
-        ) and not self.msc3861.enabled:
+        ) and not auth_delegated:
            raise ConfigError(
-                "MSC4108 requires MSC3861 to be enabled",
+                "MSC4108 requires MSC3861 or matrix_authentication_service to be enabled",
                ("experimental", "msc4108_delegation_endpoint"),
            )

--- a/synapse/crypto/event_signing.py
+++ b/synapse/crypto/event_signing.py
@@ -101,6 +101,9 @@ def compute_content_hash(
    event_dict.pop("outlier", None)
    event_dict.pop("destinations", None)

+    # N.B. no need to pop the room_id from create events in MSC4291 rooms
+    # as they shouldn't have one.
+
    event_json_bytes = encode_canonical_json(event_dict)

    hashed = hash_algorithm(event_json_bytes)
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -45,6 +45,7 @@ from signedjson.sign import SignatureVerifyException, verify_signed_json
 from unpaddedbase64 import decode_base64

 from synapse.api.constants import (
+    CREATOR_POWER_LEVEL,
    MAX_PDU_SIZE,
    EventContentFields,
    EventTypes,
@@ -64,6 +65,7 @@ from synapse.api.room_versions import (
    RoomVersion,
    RoomVersions,
 )
+from synapse.events import is_creator
 from synapse.state import CREATE_KEY
 from synapse.storage.databases.main.events_worker import EventRedactBehaviour
 from synapse.types import (
@@ -261,7 +263,8 @@ async def check_state_independent_auth_rules(
                f"Event {event.event_id} has unexpected auth_event for {k}: {auth_event_id}",
            )

-        # We also need to check that the auth event itself is not rejected.
+        # 2.3 ... If there are entries which were themselves rejected under the checks performed on receipt
+        # of a PDU, reject.
        if auth_event.rejected_reason:
            raise AuthError(
                403,
@@ -271,7 +274,7 @@ async def check_state_independent_auth_rules(

        auth_dict[k] = auth_event_id

-    # 3. If event does not have a m.room.create in its auth_events, reject.
+    # 2.4. If event does not have a m.room.create in its auth_events, reject.
    creation_event = auth_dict.get((EventTypes.Create, ""), None)
    if not creation_event:
        raise AuthError(403, "No create event in auth events")
@@ -311,13 +314,14 @@ def check_state_dependent_auth_rules(

    # Later code relies on there being a create event e.g _can_federate, _is_membership_change_allowed
    # so produce a more intelligible error if we don't have one.
-    if auth_dict.get(CREATE_KEY) is None:
+    create_event = auth_dict.get(CREATE_KEY)
+    if create_event is None:
        raise AuthError(
            403, f"Event {event.event_id} is missing a create event in auth_events."
        )

    # additional check for m.federate
-    creating_domain = get_domain_from_id(event.room_id)
+    creating_domain = get_domain_from_id(create_event.sender)
    originating_domain = get_domain_from_id(event.sender)
    if creating_domain != originating_domain:
        if not _can_federate(event, auth_dict):
@@ -470,12 +474,20 @@ def _check_create(event: "EventBase") -> None:
    if event.prev_event_ids():
        raise AuthError(403, "Create event has prev events")

-    # 1.2 If the domain of the room_id does not match the domain of the sender,
-    # reject.
-    sender_domain = get_domain_from_id(event.sender)
-    room_id_domain = get_domain_from_id(event.room_id)
-    if room_id_domain != sender_domain:
-        raise AuthError(403, "Creation event's room_id domain does not match sender's")
+    if event.room_version.msc4291_room_ids_as_hashes:
+        # 1.2 If the create event has a room_id, reject
+        if "room_id" in event:
+            raise AuthError(403, "Create event has a room_id")
+    else:
+        # 1.2 If the domain of the room_id does not match the domain of the sender,
+        # reject.
+        if not event.room_version.msc4291_room_ids_as_hashes:
+            sender_domain = get_domain_from_id(event.sender)
+            room_id_domain = get_domain_from_id(event.room_id)
+            if room_id_domain != sender_domain:
+                raise AuthError(
+                    403, "Creation event's room_id domain does not match sender's"
+                )

    # 1.3 If content.room_version is present and is not a recognised version, reject
    room_version_prop = event.content.get("room_version", "1")
@@ -492,6 +504,16 @@ def _check_create(event: "EventBase") -> None:
    ):
        raise AuthError(403, "Create event lacks a 'creator' property")

+    # 1.5 If the additional_creators field is present and is not an array of strings where each
+    # string is a valid user ID, reject.
+    if (
+        event.room_version.msc4289_creator_power_enabled
+        and EventContentFields.ADDITIONAL_CREATORS in event.content
+    ):
+        check_valid_additional_creators(
+            event.content[EventContentFields.ADDITIONAL_CREATORS]
+        )
+

 def _can_federate(event: "EventBase", auth_events: StateMap["EventBase"]) -> bool:
    creation_event = auth_events.get((EventTypes.Create, ""))
@@ -533,7 +555,13 @@ def _is_membership_change_allowed(

    target_user_id = event.state_key

-    creating_domain = get_domain_from_id(event.room_id)
+    # We need the create event in order to check if we can federate or not.
+    # If it's missing, yell loudly. Previously we only did this inside the
+    # _can_federate check.
+    create_event = auth_events.get((EventTypes.Create, ""))
+    if not create_event:
+        raise AuthError(403, "Create event missing from auth_events")
+    creating_domain = get_domain_from_id(create_event.sender)
    target_domain = get_domain_from_id(target_user_id)
    if creating_domain != target_domain:
        if not _can_federate(event, auth_events):
@@ -903,6 +931,32 @@ def _check_power_levels(
        except Exception:
            raise SynapseError(400, "Not a valid power level: %s" % (v,))

+    if room_version_obj.msc4289_creator_power_enabled:
+        # Enforce the creator does not appear in the users map
+        create_event = auth_events.get((EventTypes.Create, ""))
+        if not create_event:
+            raise SynapseError(
+                400, "Cannot check power levels without a create event in auth_events"
+            )
+        if create_event.sender in user_list:
+            raise SynapseError(
+                400,
+                "Creator user %s must not appear in content.users"
+                % (create_event.sender,),
+            )
+        additional_creators = create_event.content.get(
+            EventContentFields.ADDITIONAL_CREATORS, []
+        )
+        if additional_creators:
+            creators_in_user_list = set(additional_creators).intersection(
+                set(user_list)
+            )
+            if len(creators_in_user_list) > 0:
+                raise SynapseError(
+                    400,
+                    "Additional creators users must not appear in content.users",
+                )
+
    # Reject events with stringy power levels if required by room version
    if (
        event.type == EventTypes.PowerLevels
@@ -1028,6 +1082,9 @@ def get_user_power_level(user_id: str, auth_events: StateMap["EventBase"]) -> in
        "A create event in the auth events chain is required to calculate user power level correctly,"
        " but was not found. This indicates a bug"
    )
+    if create_event.room_version.msc4289_creator_power_enabled:
+        if is_creator(create_event, user_id):
+            return CREATOR_POWER_LEVEL
    power_level_event = get_power_level_event(auth_events)
    if power_level_event:
        level = power_level_event.content.get("users", {}).get(user_id)
@@ -1188,3 +1245,26 @@ def auth_types_for_event(
                auth_types.add(key)

    return auth_types
+
+
+def check_valid_additional_creators(additional_creators: Any) -> None:
+    """Check if the additional_creators provided is valid according to MSC4289.
+
+    The additional_creators can be supplied from an m.room.create event or from an /upgrade request.
+
+    Raises:
+        AuthError if the additional_creators is invalid for some reason.
+    """
+    if type(additional_creators) is not list:
+        raise AuthError(400, "additional_creators must be an array")
+    for entry in additional_creators:
+        if type(entry) is not str:
+            raise AuthError(400, "entry in additional_creators is not a string")
+        if not UserID.is_valid(entry):
+            raise AuthError(400, "entry in additional_creators is not a valid user ID")
+        # UserID.is_valid doesn't actually validate everything, so check the rest manually.
+        if len(entry) > 255 or len(entry.encode("utf-8")) > 255:
+            raise AuthError(
+                400,
+                "entry in additional_creators too long",
+            )
--- a/synapse/events/init.py
+++ b/synapse/events/init.py
@@ -41,10 +41,13 @@ from typing import (
 import attr
 from unpaddedbase64 import encode_base64

-from synapse.api.constants import EventTypes, RelationTypes
+from synapse.api.constants import EventContentFields, EventTypes, RelationTypes
 from synapse.api.room_versions import EventFormatVersions, RoomVersion, RoomVersions
 from synapse.synapse_rust.events import EventInternalMetadata
-from synapse.types import JsonDict, StrCollection
+from synapse.types import (
+    JsonDict,
+    StrCollection,
+)
 from synapse.util.caches import intern_dict
 from synapse.util.frozenutils import freeze

@@ -209,7 +212,6 @@ class EventBase(metaclass=abc.ABCMeta):
    content: DictProperty[JsonDict] = DictProperty("content")
    hashes: DictProperty[Dict[str, str]] = DictProperty("hashes")
    origin_server_ts: DictProperty[int] = DictProperty("origin_server_ts")
-    room_id: DictProperty[str] = DictProperty("room_id")
    sender: DictProperty[str] = DictProperty("sender")
    # TODO state_key should be Optional[str]. This is generally asserted in Synapse
    # by calling is_state() first (which ensures it is not None), but it is hard (not possible?)
@@ -224,6 +226,10 @@ class EventBase(metaclass=abc.ABCMeta):
    def event_id(self) -> str:
        raise NotImplementedError()

+    @property
+    def room_id(self) -> str:
+        raise NotImplementedError()
+
    @property
    def membership(self) -> str:
        return self.content["membership"]
@@ -386,6 +392,10 @@ class FrozenEvent(EventBase):
    def event_id(self) -> str:
        return self._event_id

+    @property
+    def room_id(self) -> str:
+        return self._dict["room_id"]
+

 class FrozenEventV2(EventBase):
    format_version = EventFormatVersions.ROOM_V3  # All events of this type are V2
@@ -443,6 +453,10 @@ class FrozenEventV2(EventBase):
        self._event_id = "$" + encode_base64(compute_event_reference_hash(self)[1])
        return self._event_id

+    @property
+    def room_id(self) -> str:
+        return self._dict["room_id"]
+
    def prev_event_ids(self) -> List[str]:
        """Returns the list of prev event IDs. The order matches the order
        specified in the event, though there is no meaning to it.
@@ -481,6 +495,67 @@ class FrozenEventV3(FrozenEventV2):
        return self._event_id


+class FrozenEventV4(FrozenEventV3):
+    """FrozenEventV4 for MSC4291 room IDs are hashes"""
+
+    format_version = EventFormatVersions.ROOM_V11_HYDRA_PLUS
+
+    """Override the room_id for m.room.create events"""
+
+    def __init__(
+        self,
+        event_dict: JsonDict,
+        room_version: RoomVersion,
+        internal_metadata_dict: Optional[JsonDict] = None,
+        rejected_reason: Optional[str] = None,
+    ):
+        super().__init__(
+            event_dict=event_dict,
+            room_version=room_version,
+            internal_metadata_dict=internal_metadata_dict,
+            rejected_reason=rejected_reason,
+        )
+        self._room_id: Optional[str] = None
+
+    @property
+    def room_id(self) -> str:
+        # if we have calculated the room ID already, don't do it again.
+        if self._room_id:
+            return self._room_id
+
+        is_create_event = self.type == EventTypes.Create and self.get_state_key() == ""
+
+        # for non-create events: use the supplied value from the JSON, as per FrozenEventV3
+        if not is_create_event:
+            self._room_id = self._dict["room_id"]
+            assert self._room_id is not None
+            return self._room_id
+
+        # for create events: calculate the room ID
+        from synapse.crypto.event_signing import compute_event_reference_hash
+
+        self._room_id = "!" + encode_base64(
+            compute_event_reference_hash(self)[1], urlsafe=True
+        )
+        return self._room_id
+
+    def auth_event_ids(self) -> StrCollection:
+        """Returns the list of auth event IDs. The order matches the order
+        specified in the event, though there is no meaning to it.
+        Returns:
+            The list of event IDs of this event's auth_events
+            Includes the creation event ID for convenience of all the codepaths
+            which expects the auth chain to include the creator ID, even though
+            it's explicitly not included on the wire. Excludes the create event
+            for the create event itself.
+        """
+        create_event_id = "$" + self.room_id[1:]
+        assert create_event_id not in self._dict["auth_events"]
+        if self.type == EventTypes.Create and self.get_state_key() == "":
+            return self._dict["auth_events"]  # should be []
+        return self._dict["auth_events"] + [create_event_id]
+
+
 def _event_type_from_format_version(
    format_version: int,
 ) -> Type[Union[FrozenEvent, FrozenEventV2, FrozenEventV3]]:
@@ -500,6 +575,8 @@ def _event_type_from_format_version(
        return FrozenEventV2
    elif format_version == EventFormatVersions.ROOM_V4_PLUS:
        return FrozenEventV3
+    elif format_version == EventFormatVersions.ROOM_V11_HYDRA_PLUS:
+        return FrozenEventV4
    else:
        raise Exception("No event format %r" % (format_version,))

@@ -559,6 +636,23 @@ def relation_from_event(event: EventBase) -> Optional[_EventRelation]:
    return _EventRelation(parent_id, rel_type, aggregation_key)


+def is_creator(create: EventBase, user_id: str) -> bool:
+    """
+    Return true if the provided user ID is the room creator.
+
+    This includes additional creators in MSC4289.
+    """
+    assert create.type == EventTypes.Create
+    if create.sender == user_id:
+        return True
+    if create.room_version.msc4289_creator_power_enabled:
+        additional_creators = set(
+            create.content.get(EventContentFields.ADDITIONAL_CREATORS, [])
+        )
+        return user_id in additional_creators
+    return False
+
+
@attr.s(slots=True, frozen=True, auto_attribs=True)
 class StrippedStateEvent:
    """
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -82,7 +82,8 @@ class EventBuilder:

    room_version: RoomVersion

-    room_id: str
+    # MSC4291 makes the room ID == the create event ID. This means the create event has no room_id.
+    room_id: Optional[str]
    type: str
    sender: str

@@ -142,7 +143,14 @@ class EventBuilder:
        Returns:
            The signed and hashed event.
        """
+        # Create events always have empty auth_events.
+        if self.type == EventTypes.Create and self.is_state() and self.state_key == "":
+            auth_event_ids = []
+
+        # Calculate auth_events for non-create events
        if auth_event_ids is None:
+            # Every non-create event must have a room ID
+            assert self.room_id is not None
            state_ids = await self._state.compute_state_after_events(
                self.room_id,
                prev_event_ids,
@@ -224,12 +232,31 @@ class EventBuilder:
            "auth_events": auth_events,
            "prev_events": prev_events,
            "type": self.type,
-            "room_id": self.room_id,
            "sender": self.sender,
            "content": self.content,
            "unsigned": self.unsigned,
            "depth": depth,
        }
+        if self.room_id is not None:
+            event_dict["room_id"] = self.room_id
+
+        if self.room_version.msc4291_room_ids_as_hashes:
+            # In MSC4291: the create event has no room ID as the create event ID /is/ the room ID.
+            if (
+                self.type == EventTypes.Create
+                and self.is_state()
+                and self._state_key == ""
+            ):
+                assert self.room_id is None
+            else:
+                # All other events do not reference the create event in auth_events, as the room ID
+                # /is/ the create event. However, the rest of the code (for consistency between room
+                # versions) assume that the create event remains part of the auth events. c.f. event
+                # class which automatically adds the create event when `.auth_event_ids()` is called
+                assert self.room_id is not None
+                create_event_id = "$" + self.room_id[1:]
+                auth_event_ids.remove(create_event_id)
+                event_dict["auth_events"] = auth_event_ids

        if self.is_state():
            event_dict["state_key"] = self._state_key
@@ -285,7 +312,7 @@ class EventBuilderFactory:
            room_version=room_version,
            type=key_values["type"],
            state_key=key_values.get("state_key"),
-            room_id=key_values["room_id"],
+            room_id=key_values.get("room_id"),
            sender=key_values["sender"],
            content=key_values.get("content", {}),
            unsigned=key_values.get("unsigned", {}),
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -26,8 +26,8 @@ from typing import (
    Any,
    Awaitable,
    Callable,
+    Collection,
    Dict,
-    Iterable,
    List,
    Mapping,
    Match,
@@ -49,6 +49,7 @@ from synapse.api.constants import (
 )
 from synapse.api.errors import Codes, SynapseError
 from synapse.api.room_versions import RoomVersion
+from synapse.logging.opentracing import SynapseTags, set_tag, trace
 from synapse.types import JsonDict, Requester

 from . import EventBase, StrippedStateEvent, make_event_from_dict
@@ -176,9 +177,12 @@ def prune_event_dict(room_version: RoomVersion, event_dict: JsonDict) -> JsonDic
        if room_version.updated_redaction_rules:
            # MSC2176 rules state that create events cannot have their `content` redacted.
            new_content = event_dict["content"]
-        elif not room_version.implicit_room_creator:
+        if not room_version.implicit_room_creator:
            # Some room versions give meaning to `creator`
            add_fields("creator")
+        if room_version.msc4291_room_ids_as_hashes:
+            # room_id is not allowed on the create event as it's derived from the event ID
+            allowed_keys.remove("room_id")

    elif event_type == EventTypes.JoinRules:
        add_fields("join_rule")
@@ -527,6 +531,10 @@ def serialize_event(
    if config.as_client_event:
        d = config.event_format(d)

+    # Ensure the room_id field is set for create events in MSC4291 rooms
+    if e.type == EventTypes.Create and e.room_version.msc4291_room_ids_as_hashes:
+        d["room_id"] = e.room_id
+
    # If the event is a redaction, the field with the redacted event ID appears
    # in a different location depending on the room version. e.redacts handles
    # fetching from the proper location; copy it to the other location for forwards-
@@ -703,9 +711,10 @@ class EventClientSerializer:
                "m.relations", {}
            ).update(serialized_aggregations)

+    @trace
    async def serialize_events(
        self,
-        events: Iterable[Union[JsonDict, EventBase]],
+        events: Collection[Union[JsonDict, EventBase]],
        time_now: int,
        *,
        config: SerializeEventConfig = _DEFAULT_SERIALIZE_EVENT_CONFIG,
@@ -724,6 +733,11 @@ class EventClientSerializer:
        Returns:
            The list of serialized events
        """
+        set_tag(
+            SynapseTags.FUNC_ARG_PREFIX + "events.length",
+            str(len(events)),
+        )
+
        return [
            await self.serialize_event(
                event,
@@ -872,6 +886,14 @@ def strip_event(event: EventBase) -> JsonDict:
    Stripped state events can only have the `sender`, `type`, `state_key` and `content`
    properties present.
    """
+    # MSC4311: Ensure the create event is available on invites and knocks.
+    # TODO: Implement the rest of MSC4311
+    if (
+        event.room_version.msc4291_room_ids_as_hashes
+        and event.type == EventTypes.Create
+        and event.get_state_key() == ""
+    ):
+        return event.get_pdu_json()

    return {
        "type": event.type,
--- a/synapse/events/validator.py
+++ b/synapse/events/validator.py
@@ -183,8 +183,18 @@ class EventValidator:
        fields an event would have
        """

+        create_event_as_room_id = (
+            event.room_version.msc4291_room_ids_as_hashes
+            and event.type == EventTypes.Create
+            and hasattr(event, "state_key")
+            and event.state_key == ""
+        )
+
        strings = ["room_id", "sender", "type"]

+        if create_event_as_room_id:
+            strings.remove("room_id")
+
        if hasattr(event, "state_key"):
            strings.append("state_key")

@@ -192,7 +202,14 @@ class EventValidator:
            if not isinstance(getattr(event, s), str):
                raise SynapseError(400, "Not '%s' a string type" % (s,))

-        RoomID.from_string(event.room_id)
+        if not create_event_as_room_id:
+            assert event.room_id is not None
+            RoomID.from_string(event.room_id)
+            if event.room_version.msc4291_room_ids_as_hashes and not RoomID.is_valid(
+                event.room_id
+            ):
+                raise SynapseError(400, f"Invalid room ID '{event.room_id}'")
+
        UserID.from_string(event.sender)

        if event.type == EventTypes.Message:
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -343,6 +343,21 @@ def event_from_pdu_json(pdu_json: JsonDict, room_version: RoomVersion) -> EventB
    if room_version.strict_canonicaljson:
        validate_canonicaljson(pdu_json)

+    # enforce that MSC4291 auth events don't include the create event.
+    # N.B. if they DO include a spurious create event, it'll fail auth checks elsewhere, so we don't
+    # need to do expensive DB lookups to find which event ID is the create event here.
+    if room_version.msc4291_room_ids_as_hashes:
+        room_id = pdu_json.get("room_id")
+        if room_id:
+            create_event_id = "$" + room_id[1:]
+            auth_events = pdu_json.get("auth_events")
+            if auth_events:
+                if create_event_id in auth_events:
+                    raise SynapseError(
+                        400,
+                        "auth_events must not contain the create event",
+                        Codes.BAD_JSON,
+                    )
    event = make_event_from_dict(pdu_json, room_version)
    return event

--- a/synapse/handlers/event_auth.py
+++ b/synapse/handlers/event_auth.py
@@ -23,6 +23,8 @@ from typing import TYPE_CHECKING, List, Mapping, Optional, Union

 from synapse import event_auth
 from synapse.api.constants import (
+    CREATOR_POWER_LEVEL,
+    EventContentFields,
    EventTypes,
    JoinRules,
    Membership,
@@ -141,6 +143,8 @@ class EventAuthHandler:
        Raises:
            SynapseError if no appropriate user is found.
        """
+        create_event_id = current_state_ids[(EventTypes.Create, "")]
+        create_event = await self._store.get_event(create_event_id)
        power_level_event_id = current_state_ids.get((EventTypes.PowerLevels, ""))
        invite_level = 0
        users_default_level = 0
@@ -156,15 +160,28 @@ class EventAuthHandler:

        # Find the user with the highest power level (only interested in local
        # users).
+        user_power_level = 0
+        chosen_user = None
        local_users_in_room = await self._store.get_local_users_in_room(room_id)
-        chosen_user = max(
-            local_users_in_room,
-            key=lambda user: users.get(user, users_default_level),
-            default=None,
-        )
+        if create_event.room_version.msc4289_creator_power_enabled:
+            creators = set(
+                create_event.content.get(EventContentFields.ADDITIONAL_CREATORS, [])
+            )
+            creators.add(create_event.sender)
+            local_creators = creators.intersection(set(local_users_in_room))
+            if len(local_creators) > 0:
+                chosen_user = local_creators.pop()  # random creator
+                user_power_level = CREATOR_POWER_LEVEL
+        else:
+            chosen_user = max(
+                local_users_in_room,
+                key=lambda user: users.get(user, users_default_level),
+                default=None,
+            )
+            # Return the chosen if they can issue invites.
+            if chosen_user:
+                user_power_level = users.get(chosen_user, users_default_level)

-        # Return the chosen if they can issue invites.
-        user_power_level = users.get(chosen_user, users_default_level)
        if chosen_user and user_power_level >= invite_level:
            logger.debug(
                "Found a user who can issue invites  %s with power level %d >= invite level %d",
--- a/synapse/handlers/federation_event.py
+++ b/synapse/handlers/federation_event.py
@@ -1728,6 +1728,9 @@ class FederationEventHandler:
                            event,
                            auth_event_id,
                        )
+                        # Drop the event from the auth_map too, else we may incorrectly persist
+                        # events which depend on this dropped event.
+                        auth_map.pop(event.event_id, None)
                        return
                    auth.append(ae)

--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -688,7 +688,10 @@ class EventCreationHandler:
                        Codes.USER_ACCOUNT_SUSPENDED,
                    )

-        if event_dict["type"] == EventTypes.Create and event_dict["state_key"] == "":
+        is_create_event = (
+            event_dict["type"] == EventTypes.Create and event_dict["state_key"] == ""
+        )
+        if is_create_event:
            room_version_id = event_dict["content"]["room_version"]
            maybe_room_version_obj = KNOWN_ROOM_VERSIONS.get(room_version_id)
            if not maybe_room_version_obj:
@@ -794,6 +797,7 @@ class EventCreationHandler:
        """
        # the only thing the user can do is join the server notices room.
        if builder.type == EventTypes.Member:
+            assert builder.room_id is not None
            membership = builder.content.get("membership", None)
            if membership == Membership.JOIN:
                return await self.store.is_server_notice_room(builder.room_id)
@@ -1259,13 +1263,40 @@ class EventCreationHandler:
                for_verification=False,
            )

+        if (
+            builder.room_version.msc4291_room_ids_as_hashes
+            and builder.type == EventTypes.Create
+            and builder.is_state()
+        ):
+            if builder.room_id is not None:
+                raise SynapseError(
+                    400,
+                    "Cannot resend m.room.create event",
+                    Codes.INVALID_PARAM,
+                )
+        else:
+            assert builder.room_id is not None
+
        if prev_event_ids is not None:
            assert len(prev_event_ids) <= 10, (
                "Attempting to create an event with %i prev_events"
                % (len(prev_event_ids),)
            )
        else:
-            prev_event_ids = await self.store.get_prev_events_for_room(builder.room_id)
+            if builder.room_id:
+                prev_event_ids = await self.store.get_prev_events_for_room(
+                    builder.room_id
+                )
+            else:
+                prev_event_ids = []  # can only happen for the create event in MSC4291 rooms
+
+        if builder.type == EventTypes.Create and builder.is_state():
+            if len(prev_event_ids) != 0:
+                raise SynapseError(
+                    400,
+                    "Cannot resend m.room.create event",
+                    Codes.INVALID_PARAM,
+                )

        # We now ought to have some `prev_events` (unless it's a create event).
        #
@@ -1529,7 +1560,7 @@ class EventCreationHandler:
        self,
        requester: Requester,
        room_id: str,
-        prev_event_id: str,
+        prev_event_id: Optional[str],
        event_dicts: Sequence[JsonDict],
        ratelimit: bool = True,
        ignore_shadow_ban: bool = False,
@@ -1560,6 +1591,12 @@ class EventCreationHandler:
            # Nothing to do.
            return

+        if prev_event_id is None:
+            # Pick the latest forward extremity as the previous event ID.
+            prev_event_ids = await self.store.get_forward_extremities_for_room(room_id)
+            prev_event_ids.sort(key=lambda x: x[2])  # Sort by depth.
+            prev_event_id = prev_event_ids[-1][0]
+
        state_groups = await self._storage_controllers.state.get_state_group_for_events(
            [prev_event_id]
        )
@@ -2228,6 +2265,7 @@ class EventCreationHandler:
                original_event.room_version, third_party_result
            )
            self.validator.validate_builder(builder)
+            assert builder.room_id is not None
        except SynapseError as e:
            raise Exception(
                "Third party rules module created an invalid event: " + e.msg,
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -82,6 +82,7 @@ from synapse.types import (
    Requester,
    RoomAlias,
    RoomID,
+    RoomIdWithDomain,
    RoomStreamToken,
    StateMap,
    StrCollection,
@@ -93,6 +94,7 @@ from synapse.types import (
 from synapse.types.handlers import ShutdownRoomParams, ShutdownRoomResponse
 from synapse.types.state import StateFilter
 from synapse.util import stringutils
+from synapse.util.async_helpers import concurrently_execute
 from synapse.util.caches.response_cache import ResponseCache
 from synapse.util.iterutils import batch_iter
 from synapse.util.stringutils import parse_and_validate_server_name
@@ -195,7 +197,13 @@ class RoomCreationHandler:
        )

    async def upgrade_room(
-        self, requester: Requester, old_room_id: str, new_version: RoomVersion
+        self,
+        requester: Requester,
+        old_room_id: str,
+        new_version: RoomVersion,
+        additional_creators: Optional[List[str]],
+        auto_member: bool = False,
+        ratelimit: bool = True,
    ) -> str:
        """Replace a room with a new room with a different version

@@ -203,6 +211,9 @@ class RoomCreationHandler:
            requester: the user requesting the upgrade
            old_room_id: the id of the room to be replaced
            new_version: the new room version to use
+            additional_creators: additional room creators, for MSC4289.
+            auto_member: Whether to automatically join local users to the new
+                room and send out invites to remote users.

        Returns:
            the new room id
@@ -210,11 +221,12 @@ class RoomCreationHandler:
        Raises:
            ShadowBanError if the requester is shadow-banned.
        """
-        await self.creation_ratelimiter.ratelimit(requester, update=False)
+        if ratelimit:
+            await self.creation_ratelimiter.ratelimit(requester, update=False)

-        # then apply the ratelimits
-        await self.common_request_ratelimiter.ratelimit(requester)
-        await self.creation_ratelimiter.ratelimit(requester)
+            # then apply the ratelimits
+            await self.common_request_ratelimiter.ratelimit(requester)
+            await self.creation_ratelimiter.ratelimit(requester)

        user_id = requester.user.to_string()

@@ -235,8 +247,29 @@ class RoomCreationHandler:
        old_room = await self.store.get_room(old_room_id)
        if old_room is None:
            raise NotFoundError("Unknown room id %s" % (old_room_id,))
+        old_room_is_public, _ = old_room

-        new_room_id = self._generate_room_id()
+        creation_event_with_context = None
+        if new_version.msc4291_room_ids_as_hashes:
+            old_room_create_event = await self.store.get_create_event_for_room(
+                old_room_id
+            )
+            creation_content = self._calculate_upgraded_room_creation_content(
+                old_room_create_event,
+                tombstone_event_id=None,
+                new_room_version=new_version,
+                additional_creators=additional_creators,
+            )
+            creation_event_with_context = await self._generate_create_event_for_room_id(
+                requester,
+                creation_content,
+                old_room_is_public,
+                new_version,
+            )
+            (create_event, _) = creation_event_with_context
+            new_room_id = create_event.room_id
+        else:
+            new_room_id = self._generate_room_id()

        # Try several times, it could fail with PartialStateConflictError
        # in _upgrade_room, cf comment in except block.
@@ -285,6 +318,9 @@ class RoomCreationHandler:
                    new_version,
                    tombstone_event,
                    tombstone_context,
+                    additional_creators,
+                    creation_event_with_context,
+                    auto_member=auto_member,
                )

                return ret
@@ -308,6 +344,11 @@ class RoomCreationHandler:
        new_version: RoomVersion,
        tombstone_event: EventBase,
        tombstone_context: synapse.events.snapshot.EventContext,
+        additional_creators: Optional[List[str]],
+        creation_event_with_context: Optional[
+            Tuple[EventBase, synapse.events.snapshot.EventContext]
+        ] = None,
+        auto_member: bool = False,
    ) -> str:
        """
        Args:
@@ -319,6 +360,10 @@ class RoomCreationHandler:
            new_version: the version to upgrade the room to
            tombstone_event: the tombstone event to send to the old room
            tombstone_context: the context for the tombstone event
+            additional_creators: additional room creators, for MSC4289.
+            creation_event_with_context: The new room's create event, for room IDs as create event IDs.
+            auto_member: Whether to automatically join local users to the new
+                room and send out invites to remote users.

        Raises:
            ShadowBanError if the requester is shadow-banned.
@@ -328,14 +373,16 @@ class RoomCreationHandler:

        logger.info("Creating new room %s to replace %s", new_room_id, old_room_id)

-        # create the new room. may raise a `StoreError` in the exceedingly unlikely
-        # event of a room ID collision.
-        await self.store.store_room(
-            room_id=new_room_id,
-            room_creator_user_id=user_id,
-            is_public=old_room[0],
-            room_version=new_version,
-        )
+        # We've already stored the room if we have the create event
+        if not creation_event_with_context:
+            # create the new room. may raise a `StoreError` in the exceedingly unlikely
+            # event of a room ID collision.
+            await self.store.store_room(
+                room_id=new_room_id,
+                room_creator_user_id=user_id,
+                is_public=old_room[0],
+                room_version=new_version,
+            )

        await self.clone_existing_room(
            requester,
@@ -343,6 +390,9 @@ class RoomCreationHandler:
            new_room_id=new_room_id,
            new_room_version=new_version,
            tombstone_event_id=tombstone_event.event_id,
+            additional_creators=additional_creators,
+            creation_event_with_context=creation_event_with_context,
+            auto_member=auto_member,
        )

        # now send the tombstone
@@ -376,6 +426,7 @@ class RoomCreationHandler:
            old_room_id,
            new_room_id,
            old_room_state,
+            additional_creators,
        )

        return new_room_id
@@ -386,6 +437,7 @@ class RoomCreationHandler:
        old_room_id: str,
        new_room_id: str,
        old_room_state: StateMap[str],
+        additional_creators: Optional[List[str]],
    ) -> None:
        """Send updated power levels in both rooms after an upgrade

@@ -394,7 +446,7 @@ class RoomCreationHandler:
            old_room_id: the id of the room to be replaced
            new_room_id: the id of the replacement room
            old_room_state: the state map for the old room
-
+            additional_creators: Additional creators in the new room.
        Raises:
            ShadowBanError if the requester is shadow-banned.
        """
@@ -450,6 +502,14 @@ class RoomCreationHandler:
            except AuthError as e:
                logger.warning("Unable to update PLs in old room: %s", e)

+        new_room_version = await self.store.get_room_version(new_room_id)
+        if new_room_version.msc4289_creator_power_enabled:
+            self._remove_creators_from_pl_users_map(
+                old_room_pl_state.content.get("users", {}),
+                requester.user.to_string(),
+                additional_creators,
+            )
+
        await self.event_creation_handler.create_and_send_nonmember_event(
            requester,
            {
@@ -464,6 +524,36 @@ class RoomCreationHandler:
            ratelimit=False,
        )

+    def _calculate_upgraded_room_creation_content(
+        self,
+        old_room_create_event: EventBase,
+        tombstone_event_id: Optional[str],
+        new_room_version: RoomVersion,
+        additional_creators: Optional[List[str]],
+    ) -> JsonDict:
+        creation_content: JsonDict = {
+            "room_version": new_room_version.identifier,
+            "predecessor": {
+                "room_id": old_room_create_event.room_id,
+            },
+        }
+        if tombstone_event_id is not None:
+            creation_content["predecessor"]["event_id"] = tombstone_event_id
+        if (
+            additional_creators is not None
+            and new_room_version.msc4289_creator_power_enabled
+        ):
+            creation_content["additional_creators"] = additional_creators
+        # Check if old room was non-federatable
+        if not old_room_create_event.content.get(EventContentFields.FEDERATE, True):
+            # If so, mark the new room as non-federatable as well
+            creation_content[EventContentFields.FEDERATE] = False
+        # Copy the room type as per MSC3818.
+        room_type = old_room_create_event.content.get(EventContentFields.ROOM_TYPE)
+        if room_type is not None:
+            creation_content[EventContentFields.ROOM_TYPE] = room_type
+        return creation_content
+
    async def clone_existing_room(
        self,
        requester: Requester,
@@ -471,6 +561,11 @@ class RoomCreationHandler:
        new_room_id: str,
        new_room_version: RoomVersion,
        tombstone_event_id: str,
+        additional_creators: Optional[List[str]],
+        creation_event_with_context: Optional[
+            Tuple[EventBase, synapse.events.snapshot.EventContext]
+        ] = None,
+        auto_member: bool = False,
    ) -> None:
        """Populate a new room based on an old room

@@ -481,24 +576,27 @@ class RoomCreationHandler:
                created with _generate_room_id())
            new_room_version: the new room version to use
            tombstone_event_id: the ID of the tombstone event in the old room.
+            additional_creators: additional room creators, for MSC4289.
+            creation_event_with_context: The create event of the new room, if the new room supports
+            room ID as create event ID hash.
+            auto_member: Whether to automatically join local users to the new
+                room and send out invites to remote users.
        """
        user_id = requester.user.to_string()

-        creation_content: JsonDict = {
-            "room_version": new_room_version.identifier,
-            "predecessor": {"room_id": old_room_id, "event_id": tombstone_event_id},
-        }
-
-        # Check if old room was non-federatable
-
        # Get old room's create event
        old_room_create_event = await self.store.get_create_event_for_room(old_room_id)

-        # Check if the create event specified a non-federatable room
-        if not old_room_create_event.content.get(EventContentFields.FEDERATE, True):
-            # If so, mark the new room as non-federatable as well
-            creation_content[EventContentFields.FEDERATE] = False
-
+        if creation_event_with_context:
+            create_event, _ = creation_event_with_context
+            creation_content = create_event.content
+        else:
+            creation_content = self._calculate_upgraded_room_creation_content(
+                old_room_create_event,
+                tombstone_event_id,
+                new_room_version,
+                additional_creators=additional_creators,
+            )
        initial_state = {}

        # Replicate relevant room events
@@ -514,11 +612,8 @@ class RoomCreationHandler:
            (EventTypes.PowerLevels, ""),
        ]

-        # Copy the room type as per MSC3818.
        room_type = old_room_create_event.content.get(EventContentFields.ROOM_TYPE)
        if room_type is not None:
-            creation_content[EventContentFields.ROOM_TYPE] = room_type
-
            # If the old room was a space, copy over the rooms in the space.
            if room_type == RoomTypes.SPACE:
                types_to_copy.append((EventTypes.SpaceChild, None))
@@ -590,6 +685,14 @@ class RoomCreationHandler:
        if current_power_level_int < needed_power_level:
            user_power_levels[user_id] = needed_power_level

+        if new_room_version.msc4289_creator_power_enabled:
+            # the creator(s) cannot be in the users map
+            self._remove_creators_from_pl_users_map(
+                user_power_levels,
+                user_id,
+                additional_creators,
+            )
+
        # We construct what the body of a call to /createRoom would look like for passing
        # to the spam checker. We don't include a preset here, as we expect the
        # initial state to contain everything we need.
@@ -618,6 +721,7 @@ class RoomCreationHandler:
            invite_list=[],
            initial_state=initial_state,
            creation_content=creation_content,
+            creation_event_with_context=creation_event_with_context,
        )

        # Transfer membership events
@@ -631,7 +735,7 @@ class RoomCreationHandler:
            # `update_membership`, however in this case its fine to bypass as
            # these bans don't need any special treatment, i.e. the sender is in
            # the room and they don't need any extra signatures, etc.
-            for batched_events in batch_iter(ban_events, 1000):
+            for batched_ban_events in batch_iter(ban_events, 1000):
                await self.event_creation_handler.create_and_send_new_client_events(
                    requester=requester,
                    room_id=new_room_id,
@@ -644,13 +748,201 @@ class RoomCreationHandler:
                            "sender": requester.user.to_string(),
                            "content": ban_event.content,
                        }
-                        for ban_event in batched_events
+                        for ban_event in batched_ban_events
                    ],
-                    ratelimit=False,
+                    ratelimit=False,  # We ratelimit the entire upgrade, not individual events.
                )

-        # XXX invites/joins
-        # XXX 3pid invites
+        if auto_member:
+            logger.info("Joining local users to %s", new_room_id)
+
+            # 1. Copy over all joins for local
+            joined_profiles = await self.store.get_users_in_room_with_profiles(
+                old_room_id
+            )
+
+            local_user_ids = [
+                user_id for user_id in joined_profiles if self.hs.is_mine_id(user_id)
+            ]
+
+            logger.info("Local user IDs %s", local_user_ids)
+
+            for batched_local_user_ids in batch_iter(local_user_ids, 1000):
+                invites_to_send = []
+
+                # For each local user we create an invite event (from the
+                # upgrading user) plus a join event.
+                for local_user_id in batched_local_user_ids:
+                    if local_user_id == user_id:
+                        # Ignore the upgrading user, as they are already in the
+                        # new room.
+                        continue
+
+                    invites_to_send.append(
+                        {
+                            "type": EventTypes.Member,
+                            "state_key": local_user_id,
+                            "room_id": new_room_id,
+                            "sender": requester.user.to_string(),
+                            "content": {
+                                "membership": Membership.INVITE,
+                            },
+                        }
+                    )
+
+                    # If the user has profile information in the previous join,
+                    # add it to the content.
+                    #
+                    # We could instead copy over the contents from the old join
+                    # event, however a) that would require us to fetch all the
+                    # old join events (which is slow), and b) generally the join
+                    # events have no extra information in them. (We also believe
+                    # that most clients don't copy this information over either,
+                    # but we could be wrong.)
+                    content_profile = {}
+                    user_profile = joined_profiles[local_user_id]
+                    if user_profile.display_name:
+                        content_profile["displayname"] = user_profile.display_name
+                    if user_profile.avatar_url:
+                        content_profile["avatar_url"] = user_profile.avatar_url
+
+                    invites_to_send.append(
+                        {
+                            "type": EventTypes.Member,
+                            "state_key": local_user_id,
+                            "room_id": new_room_id,
+                            "sender": local_user_id,
+                            "content": {
+                                "membership": Membership.JOIN,
+                                **content_profile,
+                            },
+                        }
+                    )
+
+                await self.event_creation_handler.create_and_send_new_client_events(
+                    requester=requester,
+                    room_id=new_room_id,
+                    prev_event_id=None,
+                    event_dicts=invites_to_send,
+                    ratelimit=False,  # We ratelimit the entire upgrade, not individual events.
+                )
+
+            # Invite other users if the room is not public. If the room *is*
+            # public then users can simply directly join, and inviting them as
+            # well may lead to confusion.
+
+            join_rule_content = initial_state.get((EventTypes.JoinRules, ""), None)
+            is_public = False
+            if join_rule_content:
+                is_public = join_rule_content["join_rule"] == JoinRules.PUBLIC
+
+            if not is_public:
+                # Copy invites
+                # TODO: Copy over 3pid invites as well.
+                invited_users = await self.store.get_invited_users_in_room(
+                    room_id=old_room_id
+                )
+
+                # For local users we can just batch send the invites.
+                local_invited_users = [
+                    user_id for user_id in invited_users if self.hs.is_mine_id(user_id)
+                ]
+
+                logger.info(
+                    "Joining local user IDs %s to new room %s",
+                    local_invited_users,
+                    new_room_id,
+                )
+
+                for batched_local_invited_users in batch_iter(
+                    local_invited_users, 1000
+                ):
+                    invites_to_send = []
+                    leaves_to_send = []
+
+                    # For each local user we create an invite event (from the
+                    # upgrading user), and reject the invite event in the old
+                    # room.
+                    #
+                    # This ensures that the user ends up with a single invite to
+                    # the new room (rather than multiple invites which may be
+                    # noisy and confusing).
+                    for local_user_id in batched_local_invited_users:
+                        leaves_to_send.append(
+                            {
+                                "type": EventTypes.Member,
+                                "state_key": local_user_id,
+                                "room_id": old_room_id,
+                                "sender": local_user_id,
+                                "content": {
+                                    "membership": Membership.LEAVE,
+                                },
+                            }
+                        )
+                        invites_to_send.append(
+                            {
+                                "type": EventTypes.Member,
+                                "state_key": local_user_id,
+                                "room_id": new_room_id,
+                                "sender": requester.user.to_string(),
+                                "content": {
+                                    "membership": Membership.INVITE,
+                                },
+                            }
+                        )
+
+                    await self.event_creation_handler.create_and_send_new_client_events(
+                        requester=requester,
+                        room_id=old_room_id,
+                        prev_event_id=None,
+                        event_dicts=leaves_to_send,
+                        ratelimit=False,  # We ratelimit the entire upgrade, not individual events.
+                    )
+                    await self.event_creation_handler.create_and_send_new_client_events(
+                        requester=requester,
+                        room_id=new_room_id,
+                        prev_event_id=None,
+                        event_dicts=invites_to_send,
+                        ratelimit=False,
+                    )
+
+                # For remote users we send invites one by one, as we need to
+                # send each one to the remote server.
+                #
+                # We also invite joined remote users who were in the old room.
+                remote_user_ids = [
+                    user_id
+                    for user_id in itertools.chain(invited_users, joined_profiles)
+                    if not self.hs.is_mine_id(user_id)
+                ]
+
+                logger.debug("Inviting remote user IDs %s", remote_user_ids)
+
+                async def remote_invite(remote_user: str) -> None:
+                    try:
+                        await self.room_member_handler.update_membership(
+                            requester,
+                            UserID.from_string(remote_user),
+                            new_room_id,
+                            Membership.INVITE,
+                            ratelimit=False,  # We ratelimit the entire upgrade, not individual events.
+                        )
+                    except SynapseError as e:
+                        # If we fail to invite a remote user, we log it but continue
+                        # on with the upgrade.
+                        logger.warning(
+                            "Failed to invite remote user %s to new room %s: %s",
+                            remote_user,
+                            new_room_id,
+                            e,
+                        )
+
+                # We do this concurrently, as it can take a while to invite
+                await concurrently_execute(
+                    remote_invite,
+                    remote_user_ids,
+                    10,
+                )

    async def _move_aliases_to_new_room(
        self,
@@ -904,6 +1196,7 @@ class RoomCreationHandler:
        power_level_content_override = config.get("power_level_content_override")
        if (
            power_level_content_override
+            and not room_version.msc4289_creator_power_enabled  # this validation doesn't apply in MSC4289 rooms
            and "users" in power_level_content_override
            and user_id not in power_level_content_override["users"]
        ):
@@ -933,11 +1226,41 @@ class RoomCreationHandler:
                    additional_fields=spam_check[1],
                )

-        room_id = await self._generate_and_create_room_id(
-            creator_id=user_id,
-            is_public=is_public,
-            room_version=room_version,
-        )
+        creation_content = config.get("creation_content", {})
+        # override any attempt to set room versions via the creation_content
+        creation_content["room_version"] = room_version.identifier
+
+        # trusted private chats have the invited users marked as additional creators
+        if (
+            room_version.msc4289_creator_power_enabled
+            and config.get("preset", None) == RoomCreationPreset.TRUSTED_PRIVATE_CHAT
+            and len(config.get("invite", [])) > 0
+        ):
+            # the other user(s) are additional creators
+            invitees = config.get("invite", [])
+            # we don't want to replace any additional_creators additionally specified, and we want
+            # to remove duplicates.
+            creation_content[EventContentFields.ADDITIONAL_CREATORS] = list(
+                set(creation_content.get(EventContentFields.ADDITIONAL_CREATORS, []))
+                | set(invitees)
+            )
+
+        creation_event_with_context = None
+        if room_version.msc4291_room_ids_as_hashes:
+            creation_event_with_context = await self._generate_create_event_for_room_id(
+                requester,
+                creation_content,
+                is_public,
+                room_version,
+            )
+            (create_event, _) = creation_event_with_context
+            room_id = create_event.room_id
+        else:
+            room_id = await self._generate_and_create_room_id(
+                creator_id=user_id,
+                is_public=is_public,
+                room_version=room_version,
+            )

        # Check whether this visibility value is blocked by a third party module
        allowed_by_third_party_rules = await (
@@ -974,11 +1297,6 @@ class RoomCreationHandler:
        for val in raw_initial_state:
            initial_state[(val["type"], val.get("state_key", ""))] = val["content"]

-        creation_content = config.get("creation_content", {})
-
-        # override any attempt to set room versions via the creation_content
-        creation_content["room_version"] = room_version.identifier
-
        (
            last_stream_id,
            last_sent_event_id,
@@ -995,6 +1313,7 @@ class RoomCreationHandler:
            power_level_content_override=power_level_content_override,
            creator_join_profile=creator_join_profile,
            ignore_forced_encryption=ignore_forced_encryption,
+            creation_event_with_context=creation_event_with_context,
        )

        # we avoid dropping the lock between invites, as otherwise joins can
@@ -1060,6 +1379,38 @@ class RoomCreationHandler:

        return room_id, room_alias, last_stream_id

+    async def _generate_create_event_for_room_id(
+        self,
+        creator: Requester,
+        creation_content: JsonDict,
+        is_public: bool,
+        room_version: RoomVersion,
+    ) -> Tuple[EventBase, synapse.events.snapshot.EventContext]:
+        (
+            creation_event,
+            new_unpersisted_context,
+        ) = await self.event_creation_handler.create_event(
+            creator,
+            {
+                "content": creation_content,
+                "sender": creator.user.to_string(),
+                "type": EventTypes.Create,
+                "state_key": "",
+            },
+            prev_event_ids=[],
+            depth=1,
+            state_map={},
+            for_batch=False,
+        )
+        await self.store.store_room(
+            room_id=creation_event.room_id,
+            room_creator_user_id=creator.user.to_string(),
+            is_public=is_public,
+            room_version=room_version,
+        )
+        creation_context = await new_unpersisted_context.persist(creation_event)
+        return (creation_event, creation_context)
+
    async def _send_events_for_new_room(
        self,
        creator: Requester,
@@ -1073,6 +1424,9 @@ class RoomCreationHandler:
        power_level_content_override: Optional[JsonDict] = None,
        creator_join_profile: Optional[JsonDict] = None,
        ignore_forced_encryption: bool = False,
+        creation_event_with_context: Optional[
+            Tuple[EventBase, synapse.events.snapshot.EventContext]
+        ] = None,
    ) -> Tuple[int, str, int]:
        """Sends the initial events into a new room. Sends the room creation, membership,
        and power level events into the room sequentially, then creates and batches up the
@@ -1109,7 +1463,10 @@ class RoomCreationHandler:
                user in this room.
            ignore_forced_encryption:
                Ignore encryption forced by `encryption_enabled_by_default_for_room_type` setting.
-
+            creation_event_with_context:
+                Set in MSC4291 rooms where the create event determines the room ID. If provided,
+                does not create an additional create event but instead appends the remaining new
+                events onto the provided create event.
        Returns:
            A tuple containing the stream ID, event ID and depth of the last
            event sent to the room.
@@ -1174,13 +1531,26 @@ class RoomCreationHandler:

        preset_config, config = self._room_preset_config(room_config)

-        # MSC2175 removes the creator field from the create event.
-        if not room_version.implicit_room_creator:
-            creation_content["creator"] = creator_id
-        creation_event, unpersisted_creation_context = await create_event(
-            EventTypes.Create, creation_content, False
-        )
-        creation_context = await unpersisted_creation_context.persist(creation_event)
+        if creation_event_with_context is None:
+            # MSC2175 removes the creator field from the create event.
+            if not room_version.implicit_room_creator:
+                creation_content["creator"] = creator_id
+            creation_event, unpersisted_creation_context = await create_event(
+                EventTypes.Create, creation_content, False
+            )
+            creation_context = await unpersisted_creation_context.persist(
+                creation_event
+            )
+        else:
+            (creation_event, creation_context) = creation_event_with_context
+            # we had to do the above already in order to have a room ID, so just updates local vars
+            # and continue.
+            depth = 2
+            prev_event = [creation_event.event_id]
+            state_map[(creation_event.type, creation_event.state_key)] = (
+                creation_event.event_id
+            )
+
        logger.debug("Sending %s in new room", EventTypes.Member)
        ev = await self.event_creation_handler.handle_new_client_event(
            requester=creator,
@@ -1229,7 +1599,9 @@ class RoomCreationHandler:
            # Please update the docs for `default_power_level_content_override` when
            # updating the `events` dict below
            power_level_content: JsonDict = {
-                "users": {creator_id: 100},
+                "users": {creator_id: 100}
+                if not room_version.msc4289_creator_power_enabled
+                else {},
                "users_default": 0,
                "events": {
                    EventTypes.Name: 50,
@@ -1237,7 +1609,9 @@ class RoomCreationHandler:
                    EventTypes.RoomHistoryVisibility: 100,
                    EventTypes.CanonicalAlias: 50,
                    EventTypes.RoomAvatar: 50,
-                    EventTypes.Tombstone: 100,
+                    EventTypes.Tombstone: 150
+                    if room_version.msc4289_creator_power_enabled
+                    else 100,
                    EventTypes.ServerACL: 100,
                    EventTypes.RoomEncryption: 100,
                },
@@ -1250,7 +1624,13 @@ class RoomCreationHandler:
                "historical": 100,
            }

-            if config["original_invitees_have_ops"]:
+            # original_invitees_have_ops is set on preset:trusted_private_chat which will already
+            # have set these users as additional_creators, hence don't set the PL for creators as
+            # that is invalid.
+            if (
+                config["original_invitees_have_ops"]
+                and not room_version.msc4289_creator_power_enabled
+            ):
                for invitee in invite_list:
                    power_level_content["users"][invitee] = 100

@@ -1423,6 +1803,19 @@ class RoomCreationHandler:
            )
        return preset_name, preset_config

+    def _remove_creators_from_pl_users_map(
+        self,
+        users_map: Dict[str, int],
+        creator: str,
+        additional_creators: Optional[List[str]],
+    ) -> None:
+        creators = [creator]
+        if additional_creators:
+            creators.extend(additional_creators)
+        for creator in creators:
+            # the creator(s) cannot be in the users map
+            users_map.pop(creator, None)
+
    def _generate_room_id(self) -> str:
        """Generates a random room ID.

@@ -1440,7 +1833,7 @@ class RoomCreationHandler:
            A random room ID of the form "!opaque_id:domain".
        """
        random_string = stringutils.random_string(18)
-        return RoomID(random_string, self.hs.hostname).to_string()
+        return RoomIdWithDomain(random_string, self.hs.hostname).to_string()

    async def _generate_and_create_room_id(
        self,
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -42,7 +42,7 @@ from synapse.api.errors import (
 )
 from synapse.api.ratelimiting import Ratelimiter
 from synapse.event_auth import get_named_level, get_power_level_event
-from synapse.events import EventBase
+from synapse.events import EventBase, is_creator
 from synapse.events.snapshot import EventContext
 from synapse.handlers.pagination import PURGE_ROOM_ACTION_NAME
 from synapse.handlers.profile import MAX_AVATAR_URL_LEN, MAX_DISPLAYNAME_LEN
@@ -1160,9 +1160,8 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):

        elif effective_membership_state == Membership.KNOCK:
            if not is_host_in_room:
-                # The knock needs to be sent over federation instead
-                remote_room_hosts.append(get_domain_from_id(room_id))
-
+                # we used to add the domain of the room ID to remote_room_hosts.
+                # This is not safe in MSC4291 rooms which do not have a domain.
                content["membership"] = Membership.KNOCK

                try:
@@ -2324,6 +2323,7 @@ def get_users_which_can_issue_invite(auth_events: StateMap[EventBase]) -> List[s

    # Check which members are able to invite by ensuring they're joined and have
    # the necessary power level.
+    create_event = auth_events[(EventTypes.Create, "")]
    for (event_type, state_key), event in auth_events.items():
        if event_type != EventTypes.Member:
            continue
@@ -2331,8 +2331,12 @@ def get_users_which_can_issue_invite(auth_events: StateMap[EventBase]) -> List[s
        if event.membership != Membership.JOIN:
            continue

+        if create_event.room_version.msc4289_creator_power_enabled and is_creator(
+            create_event, state_key
+        ):
+            result.append(state_key)
        # Check if the user has a custom power level.
-        if users.get(state_key, users_default_level) >= invite_level:
+        elif users.get(state_key, users_default_level) >= invite_level:
            result.append(state_key)

    return result
--- a/synapse/handlers/sliding_sync/init.py
+++ b/synapse/handlers/sliding_sync/init.py
@@ -116,7 +116,7 @@ class SlidingSyncHandler:
        sync_config: SlidingSyncConfig,
        from_token: Optional[SlidingSyncStreamToken] = None,
        timeout_ms: int = 0,
-    ) -> SlidingSyncResult:
+    ) -> Tuple[SlidingSyncResult, bool]:
        """
        Get the sync for a client if we have new data for it now. Otherwise
        wait for new data to arrive on the server. If the timeout expires, then
@@ -128,9 +128,16 @@ class SlidingSyncHandler:
            from_token: The point in the stream to sync from. Token of the end of the
                previous batch. May be `None` if this is the initial sync request.
            timeout_ms: The time in milliseconds to wait for new data to arrive. If 0,
-                we will immediately but there might not be any new data so we just return an
-                empty response.
+                we will respond immediately but there might not be any new data so we just
+                return an empty response.
+
+        Returns:
+            A tuple containing the `SlidingSyncResult` and whether we waited for new
+            activity before responding. Knowing whether we waited is useful in traces
+            to filter out long-running requests where we were just waiting.
        """
+        did_wait = False
+
        # If the user is not part of the mau group, then check that limits have
        # not been exceeded (if not part of the group by this point, almost certain
        # auth_blocking will occur)
@@ -149,7 +156,7 @@ class SlidingSyncHandler:
                logger.warning(
                    "Timed out waiting for worker to catch up. Returning empty response"
                )
-                return SlidingSyncResult.empty(from_token)
+                return SlidingSyncResult.empty(from_token), did_wait

            # If we've spent significant time waiting to catch up, take it off
            # the timeout.
@@ -185,8 +192,9 @@ class SlidingSyncHandler:
                current_sync_callback,
                from_token=from_token.stream_token,
            )
+            did_wait = True

-        return result
+        return result, did_wait

    @trace
    async def current_sync_for_user(
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -627,6 +627,15 @@ class MakeRoomAdminRestServlet(ResolveRoomIdMixin, RestServlet):
            ]
            admin_users.sort(key=lambda user: user_power[user])

+            if create_event.room_version.msc4289_creator_power_enabled:
+                creators = create_event.content.get("additional_creators", []) + [
+                    create_event.sender
+                ]
+                for creator in creators:
+                    if self.is_mine_id(creator):
+                        # include the creator as they won't be in the PL users map.
+                        admin_users.append(creator)
+
            if not admin_users:
                raise SynapseError(
                    HTTPStatus.BAD_REQUEST, "No local admin user in room"
@@ -666,7 +675,11 @@ class MakeRoomAdminRestServlet(ResolveRoomIdMixin, RestServlet):
        # updated power level event.
        new_pl_content = dict(pl_content)
        new_pl_content["users"] = dict(pl_content.get("users", {}))
-        new_pl_content["users"][user_to_add] = new_pl_content["users"][admin_user_id]
+        # give the new user the same PL as the admin, default to 100 in case there is no PL event.
+        # This means in v12+ rooms we get PL100 if the creator promotes us.
+        new_pl_content["users"][user_to_add] = new_pl_content["users"].get(
+            admin_user_id, 100
+        )

        fake_requester = create_requester(
            admin_user_id,
--- a/synapse/rest/client/room_upgrade_rest_servlet.py
+++ b/synapse/rest/client/room_upgrade_rest_servlet.py
@@ -24,6 +24,7 @@ from typing import TYPE_CHECKING, Tuple

 from synapse.api.errors import Codes, ShadowBanError, SynapseError
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
+from synapse.event_auth import check_valid_additional_creators
 from synapse.handlers.worker_lock import NEW_EVENT_DURING_PURGE_LOCK_NAME
 from synapse.http.server import HttpServer
 from synapse.http.servlet import (
@@ -85,13 +86,18 @@ class RoomUpgradeRestServlet(RestServlet):
                "Your homeserver does not support this room version",
                Codes.UNSUPPORTED_ROOM_VERSION,
            )
+        additional_creators = None
+        if new_version.msc4289_creator_power_enabled:
+            additional_creators = content.get("additional_creators")
+            if additional_creators is not None:
+                check_valid_additional_creators(additional_creators)

        try:
            async with self._worker_lock_handler.acquire_read_write_lock(
                NEW_EVENT_DURING_PURGE_LOCK_NAME, room_id, write=False
            ):
                new_room_id = await self._room_creation_handler.upgrade_room(
-                    requester, room_id, new_version
+                    requester, room_id, new_version, additional_creators
                )
        except ShadowBanError:
            # Generate a random room ID.
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -994,12 +994,18 @@ class SlidingSyncRestServlet(RestServlet):
            extensions=body.extensions,
        )

-        sliding_sync_results = await self.sliding_sync_handler.wait_for_sync_for_user(
+        (
+            sliding_sync_results,
+            did_wait,
+        ) = await self.sliding_sync_handler.wait_for_sync_for_user(
            requester,
            sync_config,
            from_token,
            timeout,
        )
+        # Knowing whether we waited is useful in traces to filter out long-running
+        # requests where we were just waiting.
+        set_tag("sliding_sync.did_wait", str(did_wait))

        # The client may have disconnected by now; don't bother to serialize the
        # response if so.
@@ -1011,6 +1017,7 @@ class SlidingSyncRestServlet(RestServlet):

        return 200, response_content

+    @trace_with_opname("sliding_sync.encode_response")
    async def encode_response(
        self,
        requester: Requester,
@@ -1031,6 +1038,7 @@ class SlidingSyncRestServlet(RestServlet):

        return response

+    @trace_with_opname("sliding_sync.encode_lists")
    def encode_lists(
        self, lists: Mapping[str, SlidingSyncResult.SlidingWindowList]
    ) -> JsonDict:
@@ -1052,6 +1060,7 @@ class SlidingSyncRestServlet(RestServlet):

        return serialized_lists

+    @trace_with_opname("sliding_sync.encode_rooms")
    async def encode_rooms(
        self,
        requester: Requester,
@@ -1172,6 +1181,7 @@ class SlidingSyncRestServlet(RestServlet):

        return serialized_rooms

+    @trace_with_opname("sliding_sync.encode_extensions")
    async def encode_extensions(
        self, requester: Requester, extensions: SlidingSyncResult.Extensions
    ) -> JsonDict:
--- a/synapse/state/init.py
+++ b/synapse/state/init.py
@@ -54,6 +54,7 @@ from synapse.logging.opentracing import tag_args, trace
 from synapse.metrics import SERVER_NAME_LABEL
 from synapse.replication.http.state import ReplicationUpdateCurrentStateRestServlet
 from synapse.state import v1, v2
+from synapse.storage.databases.main.event_federation import StateDifference
 from synapse.storage.databases.main.events_worker import EventRedactBehaviour
 from synapse.types import StateMap, StrCollection
 from synapse.types.state import StateFilter
@@ -990,17 +991,35 @@ class StateResolutionStore:
        )

    def get_auth_chain_difference(
-        self, room_id: str, state_sets: List[Set[str]]
-    ) -> Awaitable[Set[str]]:
-        """Given sets of state events figure out the auth chain difference (as
+        self,
+        room_id: str,
+        state_sets: List[Set[str]],
+        conflicted_state: Optional[Set[str]],
+        additional_backwards_reachable_conflicted_events: Optional[Set[str]],
+    ) -> Awaitable[StateDifference]:
+        """ "Given sets of state events figure out the auth chain difference (as
        per state res v2 algorithm).

-        This equivalent to fetching the full auth chain for each set of state
+        This is equivalent to fetching the full auth chain for each set of state
        and returning the events that don't appear in each and every auth
        chain.

+        If conflicted_state is not None, calculate and return the conflicted sub-graph as per
+        state res v2.1. The event IDs in the conflicted state MUST be a subset of the event IDs in
+        state_sets.
+
+        If additional_backwards_reachable_conflicted_events is set, the provided events are included
+        when calculating the conflicted subgraph. This is primarily useful for calculating the
+        subgraph across a combination of persisted and unpersisted events.
+
        Returns:
-            An awaitable that resolves to a set of event IDs.
+            information on the auth chain difference, and also the conflicted subgraph if
+            conflicted_state is not None
        """

-        return self.main_store.get_auth_chain_difference(room_id, state_sets)
+        return self.main_store.get_auth_chain_difference_extended(
+            room_id,
+            state_sets,
+            conflicted_state,
+            additional_backwards_reachable_conflicted_events,
+        )
--- a/synapse/state/v2.py
+++ b/synapse/state/v2.py
@@ -39,10 +39,11 @@ from typing import (
 )

 from synapse import event_auth
-from synapse.api.constants import EventTypes
+from synapse.api.constants import CREATOR_POWER_LEVEL, EventTypes
 from synapse.api.errors import AuthError
-from synapse.api.room_versions import RoomVersion
-from synapse.events import EventBase
+from synapse.api.room_versions import RoomVersion, StateResolutionVersions
+from synapse.events import EventBase, is_creator
+from synapse.storage.databases.main.event_federation import StateDifference
 from synapse.types import MutableStateMap, StateMap, StrCollection

 logger = logging.getLogger(__name__)
@@ -63,8 +64,12 @@ class StateResolutionStore(Protocol):
    ) -> Awaitable[Dict[str, EventBase]]: ...

    def get_auth_chain_difference(
-        self, room_id: str, state_sets: List[Set[str]]
-    ) -> Awaitable[Set[str]]: ...
+        self,
+        room_id: str,
+        state_sets: List[Set[str]],
+        conflicted_state: Optional[Set[str]],
+        additional_backwards_reachable_conflicted_events: Optional[set[str]],
+    ) -> Awaitable[StateDifference]: ...


 # We want to await to the reactor occasionally during state res when dealing
@@ -123,12 +128,17 @@ async def resolve_events_with_store(
    logger.debug("%d conflicted state entries", len(conflicted_state))
    logger.debug("Calculating auth chain difference")

-    # Also fetch all auth events that appear in only some of the state sets'
-    # auth chains.
+    conflicted_set: Optional[Set[str]] = None
+    if room_version.state_res == StateResolutionVersions.V2_1:
+        # calculate the conflicted subgraph
+        conflicted_set = set(itertools.chain.from_iterable(conflicted_state.values()))
    auth_diff = await _get_auth_chain_difference(
-        room_id, state_sets, event_map, state_res_store
+        room_id,
+        state_sets,
+        event_map,
+        state_res_store,
+        conflicted_set,
    )
-
    full_conflicted_set = set(
        itertools.chain(
            itertools.chain.from_iterable(conflicted_state.values()), auth_diff
@@ -168,15 +178,26 @@ async def resolve_events_with_store(

    logger.debug("sorted %d power events", len(sorted_power_events))

+    # v2.1 starts iterative auth checks from the empty set and not the unconflicted state.
+    # It relies on IAC behaviour which populates the base state with the events from auth_events
+    # if the state tuple is missing from the base state. This ensures the base state is only
+    # populated from auth_events rather than whatever the unconflicted state is (which could be
+    # completely bogus).
+    base_state = (
+        {}
+        if room_version.state_res == StateResolutionVersions.V2_1
+        else unconflicted_state
+    )
+
    # Now sequentially auth each one
    resolved_state = await _iterative_auth_checks(
        clock,
        room_id,
        room_version,
-        sorted_power_events,
-        unconflicted_state,
-        event_map,
-        state_res_store,
+        event_ids=sorted_power_events,
+        base_state=base_state,
+        event_map=event_map,
+        state_res_store=state_res_store,
    )

    logger.debug("resolved power events")
@@ -239,13 +260,23 @@ async def _get_power_level_for_sender(
    event = await _get_event(room_id, event_id, event_map, state_res_store)

    pl = None
+    create = None
    for aid in event.auth_event_ids():
        aev = await _get_event(
            room_id, aid, event_map, state_res_store, allow_none=True
        )
        if aev and (aev.type, aev.state_key) == (EventTypes.PowerLevels, ""):
            pl = aev
-            break
+        if aev and (aev.type, aev.state_key) == (EventTypes.Create, ""):
+            create = aev
+
+    if event.type != EventTypes.Create:
+        # we should always have a create event
+        assert create is not None
+
+    if create and create.room_version.msc4289_creator_power_enabled:
+        if is_creator(create, event.sender):
+            return CREATOR_POWER_LEVEL

    if pl is None:
        # Couldn't find power level. Check if they're the creator of the room
@@ -286,6 +317,7 @@ async def _get_auth_chain_difference(
    state_sets: Sequence[StateMap[str]],
    unpersisted_events: Dict[str, EventBase],
    state_res_store: StateResolutionStore,
+    conflicted_state: Optional[Set[str]],
 ) -> Set[str]:
    """Compare the auth chains of each state set and return the set of events
    that only appear in some, but not all of the auth chains.
@@ -294,11 +326,18 @@ async def _get_auth_chain_difference(
        state_sets: The input state sets we are trying to resolve across.
        unpersisted_events: A map from event ID to EventBase containing all unpersisted
            events involved in this resolution.
-        state_res_store:
+        state_res_store: A way to retrieve events and extract graph information on the auth chains.
+        conflicted_state: which event IDs are conflicted. Used in v2.1 for calculating the conflicted
+            subgraph.

    Returns:
-        The auth difference of the given state sets, as a set of event IDs.
+        The auth difference of the given state sets, as a set of event IDs. Also includes the
+        conflicted subgraph if `conflicted_state` is set.
    """
+    is_state_res_v21 = conflicted_state is not None
+    num_conflicted_state = (
+        len(conflicted_state) if conflicted_state is not None else None
+    )

    # The `StateResolutionStore.get_auth_chain_difference` function assumes that
    # all events passed to it (and their auth chains) have been persisted
@@ -318,14 +357,19 @@ async def _get_auth_chain_difference(
    # the event's auth chain with the events in `unpersisted_events` *plus* their
    # auth event IDs.
    events_to_auth_chain: Dict[str, Set[str]] = {}
+    # remember the forward links when doing the graph traversal, we'll need it for v2.1 checks
+    # This is a map from an event to the set of events that contain it as an auth event.
+    event_to_next_event: Dict[str, Set[str]] = {}
    for event in unpersisted_events.values():
        chain = {event.event_id}
        events_to_auth_chain[event.event_id] = chain

        to_search = [event]
        while to_search:
-            for auth_id in to_search.pop().auth_event_ids():
+            next_event = to_search.pop()
+            for auth_id in next_event.auth_event_ids():
                chain.add(auth_id)
+                event_to_next_event.setdefault(auth_id, set()).add(next_event.event_id)
                auth_event = unpersisted_events.get(auth_id)
                if auth_event:
                    to_search.append(auth_event)
@@ -335,6 +379,8 @@ async def _get_auth_chain_difference(
    #
    # Note: If there are no `unpersisted_events` (which is the common case), we can do a
    # much simpler calculation.
+    additional_backwards_reachable_conflicted_events: Set[str] = set()
+    unpersisted_conflicted_events: Set[str] = set()
    if unpersisted_events:
        # The list of state sets to pass to the store, where each state set is a set
        # of the event ids making up the state. This is similar to `state_sets`,
@@ -372,7 +418,16 @@ async def _get_auth_chain_difference(
                    )
                else:
                    set_ids.add(event_id)
-
+        if conflicted_state:
+            for conflicted_event_id in conflicted_state:
+                # presence in this map means it is unpersisted.
+                event_chain = events_to_auth_chain.get(conflicted_event_id)
+                if event_chain is not None:
+                    unpersisted_conflicted_events.add(conflicted_event_id)
+                    # tell the DB layer that we have some unpersisted conflicted events
+                    additional_backwards_reachable_conflicted_events.update(
+                        e for e in event_chain if e not in unpersisted_events
+                    )
        # The auth chain difference of the unpersisted events of the state sets
        # is calculated by taking the difference between the union and
        # intersections.
@@ -384,12 +439,89 @@ async def _get_auth_chain_difference(
        auth_difference_unpersisted_part = ()
        state_sets_ids = [set(state_set.values()) for state_set in state_sets]

-    difference = await state_res_store.get_auth_chain_difference(
-        room_id, state_sets_ids
-    )
-    difference.update(auth_difference_unpersisted_part)
+    if conflicted_state:
+        # to ensure that conflicted state is a subset of state set IDs, we need to remove UNPERSISTED
+        # conflicted state set ids as we removed them above.
+        conflicted_state = conflicted_state - unpersisted_conflicted_events

-    return difference
+    difference = await state_res_store.get_auth_chain_difference(
+        room_id,
+        state_sets_ids,
+        conflicted_state,
+        additional_backwards_reachable_conflicted_events,
+    )
+    difference.auth_difference.update(auth_difference_unpersisted_part)
+
+    # if we're doing v2.1 we may need to add or expand the conflicted subgraph
+    if (
+        is_state_res_v21
+        and difference.conflicted_subgraph is not None
+        and unpersisted_events
+    ):
+        # we always include the conflicted events themselves in the subgraph.
+        if conflicted_state:
+            difference.conflicted_subgraph.update(conflicted_state)
+        # we may need to expand the subgraph in the case where the subgraph starts in the DB and
+        # ends in unpersisted events. To do this, we first need to see where the subgraph got up to,
+        # which we can do by finding the intersection between the additional backwards reachable
+        # conflicted events and the conflicted subgraph. Events in both sets mean A) some unpersisted
+        # conflicted event could backwards reach it and B) some persisted conflicted event could forward
+        # reach it.
+        subgraph_frontier = difference.conflicted_subgraph.intersection(
+            additional_backwards_reachable_conflicted_events
+        )
+        # we can now combine the 2 scenarios:
+        #  - subgraph starts in DB and ends in unpersisted
+        #  - subgraph starts in unpersisted and ends in unpersisted
+        # by expanding the frontier into unpersisted events.
+        # The frontier is currently all persisted events. We want to expand this into unpersisted
+        # events. Mark every forwards reachable event from the frontier in the forwards_conflicted_set
+        # but NOT the backwards conflicted set. This mirrors what the DB layer does but in reverse:
+        # we supplied events which are backwards reachable to the DB and now the DB is providing
+        # forwards reachable events from the DB.
+        forwards_conflicted_set: Set[str] = set()
+        # we include unpersisted conflicted events here to process exclusive unpersisted subgraphs
+        search_queue = subgraph_frontier.union(unpersisted_conflicted_events)
+        while search_queue:
+            frontier_event = search_queue.pop()
+            next_event_ids = event_to_next_event.get(frontier_event, set())
+            search_queue.update(next_event_ids)
+            forwards_conflicted_set.add(frontier_event)
+
+        # we've already calculated the backwards form as this is the auth chain for each
+        # unpersisted conflicted event.
+        backwards_conflicted_set: Set[str] = set()
+        for uce in unpersisted_conflicted_events:
+            backwards_conflicted_set.update(events_to_auth_chain.get(uce, []))
+
+        # the unpersisted conflicted subgraph is the intersection of the backwards/forwards sets
+        conflicted_subgraph_unpersisted_part = backwards_conflicted_set.intersection(
+            forwards_conflicted_set
+        )
+        # print(f"event_to_next_event={event_to_next_event}")
+        # print(f"unpersisted_conflicted_events={unpersisted_conflicted_events}")
+        # print(f"unperssited backwards_conflicted_set={backwards_conflicted_set}")
+        # print(f"unperssited forwards_conflicted_set={forwards_conflicted_set}")
+        difference.conflicted_subgraph.update(conflicted_subgraph_unpersisted_part)
+
+    if difference.conflicted_subgraph:
+        old_events = difference.auth_difference.union(
+            conflicted_state if conflicted_state else set()
+        )
+        additional_events = difference.conflicted_subgraph.difference(old_events)
+
+        logger.debug(
+            "v2.1 %s additional events replayed=%d num_conflicts=%d conflicted_subgraph=%d auth_difference=%d",
+            room_id,
+            len(additional_events),
+            num_conflicted_state,
+            len(difference.conflicted_subgraph),
+            len(difference.auth_difference),
+        )
+        # State res v2.1 includes the conflicted subgraph in the difference
+        return difference.auth_difference.union(difference.conflicted_subgraph)
+
+    return difference.auth_difference


 def _seperate(
--- a/synapse/storage/databases/main/event_federation.py
+++ b/synapse/storage/databases/main/event_federation.py
@@ -114,6 +114,12 @@ _LONGEST_BACKOFF_PERIOD_MILLISECONDS = (
 assert 0 < _LONGEST_BACKOFF_PERIOD_MILLISECONDS <= ((2**31) - 1)


+# We use 2^53-1 as a "very large number", it has no particular
+# importance other than knowing synapse can support it (given canonical json
+# requires it).
+MAX_CHAIN_LENGTH = (2**53) - 1
+
+
 # All the info we need while iterating the DAG while backfilling
@attr.s(frozen=True, slots=True, auto_attribs=True)
 class BackfillQueueNavigationItem:
@@ -123,6 +129,14 @@ class BackfillQueueNavigationItem:
    type: str


+@attr.s(frozen=True, slots=True, auto_attribs=True)
+class StateDifference:
+    # The event IDs in the auth difference.
+    auth_difference: Set[str]
+    # The event IDs in the conflicted state subgraph. Used in v2.1 only.
+    conflicted_subgraph: Optional[Set[str]]
+
+
 class _NoChainCoverIndex(Exception):
    def __init__(self, room_id: str):
        super().__init__("Unexpectedly no chain cover for events in %s" % (room_id,))
@@ -471,17 +485,41 @@ class EventFederationWorkerStore(
        return results

    async def get_auth_chain_difference(
-        self, room_id: str, state_sets: List[Set[str]]
+        self,
+        room_id: str,
+        state_sets: List[Set[str]],
    ) -> Set[str]:
-        """Given sets of state events figure out the auth chain difference (as
+        state_diff = await self.get_auth_chain_difference_extended(
+            room_id, state_sets, None, None
+        )
+        return state_diff.auth_difference
+
+    async def get_auth_chain_difference_extended(
+        self,
+        room_id: str,
+        state_sets: List[Set[str]],
+        conflicted_set: Optional[Set[str]],
+        additional_backwards_reachable_conflicted_events: Optional[Set[str]],
+    ) -> StateDifference:
+        """ "Given sets of state events figure out the auth chain difference (as
        per state res v2 algorithm).

-        This equivalent to fetching the full auth chain for each set of state
+        This is equivalent to fetching the full auth chain for each set of state
        and returning the events that don't appear in each and every auth
        chain.

+        If conflicted_set is not None, calculate and return the conflicted sub-graph as per
+        state res v2.1. The event IDs in the conflicted set MUST be a subset of the event IDs in
+        state_sets.
+
+        If additional_backwards_reachable_conflicted_events is set, the provided events are included
+        when calculating the conflicted subgraph. This is primarily useful for calculating the
+        subgraph across a combination of persisted and unpersisted events. The event IDs in this set
+        MUST be a subset of the event IDs in state_sets.
+
        Returns:
-            The set of the difference in auth chains.
+            information on the auth chain difference, and also the conflicted subgraph if
+            conflicted_set is not None
        """

        # Check if we have indexed the room so we can use the chain cover
@@ -495,6 +533,8 @@ class EventFederationWorkerStore(
                    self._get_auth_chain_difference_using_cover_index_txn,
                    room_id,
                    state_sets,
+                    conflicted_set,
+                    additional_backwards_reachable_conflicted_events,
                )
            except _NoChainCoverIndex:
                # For whatever reason we don't actually have a chain cover index
@@ -503,25 +543,48 @@ class EventFederationWorkerStore(
                if not self.tests_allow_no_chain_cover_index:
                    raise

-        return await self.db_pool.runInteraction(
+        # It's been 4 years since we added chain cover, so we expect all rooms to have it.
+        # If they don't, we will error out when trying to do state res v2.1
+        if conflicted_set is not None:
+            raise _NoChainCoverIndex(room_id)
+
+        auth_diff = await self.db_pool.runInteraction(
            "get_auth_chain_difference",
            self._get_auth_chain_difference_txn,
            state_sets,
        )
+        return StateDifference(auth_difference=auth_diff, conflicted_subgraph=None)

    def _get_auth_chain_difference_using_cover_index_txn(
-        self, txn: LoggingTransaction, room_id: str, state_sets: List[Set[str]]
-    ) -> Set[str]:
+        self,
+        txn: LoggingTransaction,
+        room_id: str,
+        state_sets: List[Set[str]],
+        conflicted_set: Optional[Set[str]] = None,
+        additional_backwards_reachable_conflicted_events: Optional[Set[str]] = None,
+    ) -> StateDifference:
        """Calculates the auth chain difference using the chain index.

        See docs/auth_chain_difference_algorithm.md for details
        """
+        is_state_res_v21 = conflicted_set is not None

        # First we look up the chain ID/sequence numbers for all the events, and
        # work out the chain/sequence numbers reachable from each state set.

        initial_events = set(state_sets[0]).union(*state_sets[1:])

+        if is_state_res_v21:
+            # Sanity check v2.1 fields
+            assert conflicted_set is not None
+            assert conflicted_set.issubset(initial_events)
+            # It's possible for the conflicted_set to be empty if all the conflicts are in
+            # unpersisted events, so we don't assert that conflicted_set has len > 0
+            if additional_backwards_reachable_conflicted_events:
+                assert additional_backwards_reachable_conflicted_events.issubset(
+                    initial_events
+                )
+
        # Map from event_id -> (chain ID, seq no)
        chain_info: Dict[str, Tuple[int, int]] = {}

@@ -557,14 +620,14 @@ class EventFederationWorkerStore(
        events_missing_chain_info = initial_events.difference(chain_info)

        # The result set to return, i.e. the auth chain difference.
-        result: Set[str] = set()
+        auth_difference_result: Set[str] = set()

        if events_missing_chain_info:
            # For some reason we have events we haven't calculated the chain
            # index for, so we need to handle those separately. This should only
            # happen for older rooms where the server doesn't have all the auth
            # events.
-            result = self._fixup_auth_chain_difference_sets(
+            auth_difference_result = self._fixup_auth_chain_difference_sets(
                txn,
                room_id,
                state_sets=state_sets,
@@ -583,6 +646,45 @@ class EventFederationWorkerStore(

            fetch_chain_info(new_events_to_fetch)

+        # State Res v2.1 needs extra data structures to calculate the conflicted subgraph which
+        # are outlined below.
+
+        # A subset of chain_info for conflicted events only, as we need to
+        # loop all conflicted chain positions. Map from event_id -> (chain ID, seq no)
+        conflicted_chain_positions: Dict[str, Tuple[int, int]] = {}
+        # For each chain, remember the positions where conflicted events are.
+        # We need this for calculating the forward reachable events.
+        conflicted_chain_to_seq: Dict[int, Set[int]] = {}  # chain_id => {seq_num}
+        #  A subset of chain_info for additional backwards reachable events only, as we need to
+        # loop all additional backwards reachable events for calculating backwards reachable events.
+        additional_backwards_reachable_positions: Dict[
+            str, Tuple[int, int]
+        ] = {}  # event_id => (chain_id, seq_num)
+        # These next two fields are critical as the intersection of them is the conflicted subgraph.
+        # We'll populate them when we walk the chain links.
+        # chain_id => max(seq_num) backwards reachable (e.g 4 means 1,2,3,4 are backwards reachable)
+        conflicted_backwards_reachable: Dict[int, int] = {}
+        # chain_id => min(seq_num) forwards reachable (e.g 4 means 4,5,6..n are forwards reachable)
+        conflicted_forwards_reachable: Dict[int, int] = {}
+
+        # populate the v2.1 data structures
+        if is_state_res_v21:
+            assert conflicted_set is not None
+            # provide chain positions for each conflicted event
+            for conflicted_event_id in conflicted_set:
+                (chain_id, seq_num) = chain_info[conflicted_event_id]
+                conflicted_chain_positions[conflicted_event_id] = (chain_id, seq_num)
+                conflicted_chain_to_seq.setdefault(chain_id, set()).add(seq_num)
+            if additional_backwards_reachable_conflicted_events:
+                for (
+                    additional_event_id
+                ) in additional_backwards_reachable_conflicted_events:
+                    (chain_id, seq_num) = chain_info[additional_event_id]
+                    additional_backwards_reachable_positions[additional_event_id] = (
+                        chain_id,
+                        seq_num,
+                    )
+
        # Corresponds to `state_sets`, except as a map from chain ID to max
        # sequence number reachable from the state set.
        set_to_chain: List[Dict[int, int]] = []
@@ -600,6 +702,8 @@ class EventFederationWorkerStore(

        # (We need to take a copy of `seen_chains` as the function mutates it)
        for links in self._get_chain_links(txn, set(seen_chains)):
+            # `links` encodes the backwards reachable events _from a single chain_ all the way to
+            # the root of the graph.
            for chains in set_to_chain:
                for chain_id in links:
                    if chain_id not in chains:
@@ -608,6 +712,87 @@ class EventFederationWorkerStore(
                    _materialize(chain_id, chains[chain_id], links, chains)

                seen_chains.update(chains)
+            if is_state_res_v21:
+                # Apply v2.1 conflicted event reachability checks.
+                #
+                #  A <-- B <-- C <-- D <-- E
+                #
+                # Backwards reachable from C = {A,B}
+                # Forwards reachable from C = {D,E}
+
+                # this handles calculating forwards reachable information and updates
+                # conflicted_forwards_reachable.
+                accumulate_forwards_reachable_events(
+                    conflicted_forwards_reachable,
+                    links,
+                    conflicted_chain_positions,
+                )
+
+                # handle backwards reachable information
+                for (
+                    conflicted_chain_id,
+                    conflicted_chain_seq,
+                ) in conflicted_chain_positions.values():
+                    if conflicted_chain_id not in links:
+                        # This conflicted event does not lie on the path to the root.
+                        continue
+
+                    # The conflicted chain position itself encodes reachability information
+                    # _within_ the chain. Set it now before walking to other links.
+                    conflicted_backwards_reachable[conflicted_chain_id] = max(
+                        conflicted_chain_seq,
+                        conflicted_backwards_reachable.get(conflicted_chain_id, 0),
+                    )
+
+                    # Build backwards reachability paths. This is the same as what the auth difference
+                    # code does. We find which chain the conflicted event
+                    # belongs to then walk it backwards to the root. We store reachability info
+                    # for all conflicted events in the same map 'conflicted_backwards_reachable'
+                    # as we don't care about the paths themselves.
+                    _materialize(
+                        conflicted_chain_id,
+                        conflicted_chain_seq,
+                        links,
+                        conflicted_backwards_reachable,
+                    )
+                # Mark some extra events as backwards reachable. This is used when we have some
+                # unpersisted events and want to know the subgraph across the persisted/unpersisted
+                # boundary:
+                #                  |
+                #  A <-- B <-- C <-|- D <-- E <-- F
+                #     persisted    |   unpersisted
+                #
+                # Assume {B,E} are conflicted, we want to return {B,C,D,E}
+                #
+                # The unpersisted code ensures it passes C as an additional backwards reachable
+                # event. C is NOT a conflicted event, but we do need to consider it as part of
+                # the backwards reachable set. When we then calculate the forwards reachable set
+                # from B, C will be in both the backwards and forwards reachable sets and hence
+                # will be included in the conflicted subgraph.
+                for (
+                    additional_chain_id,
+                    additional_chain_seq,
+                ) in additional_backwards_reachable_positions.values():
+                    if additional_chain_id not in links:
+                        # The additional backwards reachable event does not lie on the path to the root.
+                        continue
+
+                    # the additional event chain position itself encodes reachability information.
+                    # It means that position and all positions earlier in that chain are backwards reachable
+                    # by some unpersisted conflicted event.
+                    conflicted_backwards_reachable[additional_chain_id] = max(
+                        additional_chain_seq,
+                        conflicted_backwards_reachable.get(additional_chain_id, 0),
+                    )
+
+                    # Now walk the chains back, marking backwards reachable events.
+                    # This is the same thing we do for auth difference / conflicted events.
+                    _materialize(
+                        additional_chain_id,  # walk all links back, marking them as backwards reachable
+                        additional_chain_seq,
+                        links,
+                        conflicted_backwards_reachable,
+                    )

        # Now for each chain we figure out the maximum sequence number reachable
        # from *any* state set and the minimum sequence number reachable from
@@ -616,7 +801,7 @@ class EventFederationWorkerStore(

        # Mapping from chain ID to the range of sequence numbers that should be
        # pulled from the database.
-        chain_to_gap: Dict[int, Tuple[int, int]] = {}
+        auth_diff_chain_to_gap: Dict[int, Tuple[int, int]] = {}

        for chain_id in seen_chains:
            min_seq_no = min(chains.get(chain_id, 0) for chains in set_to_chain)
@@ -629,15 +814,76 @@ class EventFederationWorkerStore(
                for seq_no in range(min_seq_no + 1, max_seq_no + 1):
                    event_id = chain_to_event.get(chain_id, {}).get(seq_no)
                    if event_id:
-                        result.add(event_id)
+                        auth_difference_result.add(event_id)
                    else:
-                        chain_to_gap[chain_id] = (min_seq_no, max_seq_no)
+                        auth_diff_chain_to_gap[chain_id] = (min_seq_no, max_seq_no)
                        break

-        if not chain_to_gap:
-            # If there are no gaps to fetch, we're done!
-            return result
+        conflicted_subgraph_result: Set[str] = set()
+        # Mapping from chain ID to the range of sequence numbers that should be
+        # pulled from the database.
+        conflicted_subgraph_chain_to_gap: Dict[int, Tuple[int, int]] = {}
+        if is_state_res_v21:
+            # also include the conflicted subgraph using backward/forward reachability info from all
+            # the conflicted events. To calculate this, we want to extract the intersection between
+            # the backwards and forwards reachability sets, e.g:
+            #     A <- B <- C <- D <- E
+            #    Assume B and D are conflicted so we want {C} as the conflicted subgraph.
+            #    B_backwards={A}, B_forwards={C,D,E}
+            #    D_backwards={A,B,C} D_forwards={E}
+            #    ALL_backwards={A,B,C} ALL_forwards={C,D,E}
+            #    Intersection(ALL_backwards, ALL_forwards) = {C}
+            #
+            # It's worth noting that once we have the ALL_ sets, we no longer care about the paths.
+            # We're dealing with chains and not singular events, but we've already got the ALL_ sets.
+            # As such, we can inspect each chain in isolation and check for overlapping sequence
+            # numbers:
+            #             1,2,3,4,5 Seq Num
+            #    Chain N [A,B,C,D,E]
+            #
+            # if (N,4) is in the backwards set and (N,2) is in the forwards set, then the
+            # intersection is events between 2 < 4. We will include the conflicted events themselves
+            # in the subgraph, but they will already be, hence the full set of events is {B,C,D}.
+            for chain_id, backwards_seq_num in conflicted_backwards_reachable.items():
+                forwards_seq_num = conflicted_forwards_reachable.get(chain_id)
+                if forwards_seq_num is None:
+                    continue  # this chain isn't in both sets so can't intersect
+                if forwards_seq_num > backwards_seq_num:
+                    continue  # this chain is in both sets but they don't overap
+                for seq_no in range(
+                    forwards_seq_num, backwards_seq_num + 1
+                ):  # inclusive of both
+                    event_id = chain_to_event.get(chain_id, {}).get(seq_no)
+                    if event_id:
+                        conflicted_subgraph_result.add(event_id)
+                    else:
+                        conflicted_subgraph_chain_to_gap[chain_id] = (
+                            # _fetch_event_ids_from_chains_txn is exclusive of the min value
+                            forwards_seq_num - 1,
+                            backwards_seq_num,
+                        )
+                        break

+        if auth_diff_chain_to_gap:
+            auth_difference_result.update(
+                self._fetch_event_ids_from_chains_txn(txn, auth_diff_chain_to_gap)
+            )
+        if conflicted_subgraph_chain_to_gap:
+            conflicted_subgraph_result.update(
+                self._fetch_event_ids_from_chains_txn(
+                    txn, conflicted_subgraph_chain_to_gap
+                )
+            )
+
+        return StateDifference(
+            auth_difference=auth_difference_result,
+            conflicted_subgraph=conflicted_subgraph_result,
+        )
+
+    def _fetch_event_ids_from_chains_txn(
+        self, txn: LoggingTransaction, chains: Dict[int, Tuple[int, int]]
+    ) -> Set[str]:
+        result: Set[str] = set()
        if isinstance(self.database_engine, PostgresEngine):
            # We can use `execute_values` to efficiently fetch the gaps when
            # using postgres.
@@ -651,7 +897,7 @@ class EventFederationWorkerStore(

            args = [
                (chain_id, min_no, max_no)
-                for chain_id, (min_no, max_no) in chain_to_gap.items()
+                for chain_id, (min_no, max_no) in chains.items()
            ]

            rows = txn.execute_values(sql, args)
@@ -662,10 +908,9 @@ class EventFederationWorkerStore(
                SELECT event_id FROM event_auth_chains
                WHERE chain_id = ? AND ? < sequence_number AND sequence_number <= ?
            """
-            for chain_id, (min_no, max_no) in chain_to_gap.items():
+            for chain_id, (min_no, max_no) in chains.items():
                txn.execute(sql, (chain_id, min_no, max_no))
                result.update(r for (r,) in txn)
-
        return result

    def _fixup_auth_chain_difference_sets(
@@ -2165,6 +2410,7 @@ def _materialize(
    origin_sequence_number: int,
    links: Dict[int, List[Tuple[int, int, int]]],
    materialized: Dict[int, int],
+    backwards: bool = True,
 ) -> None:
    """Helper function for fetching auth chain links. For a given origin chain
    ID / sequence number and a dictionary of links, updates the materialized
@@ -2181,6 +2427,7 @@ def _materialize(
            target sequence number.
        materialized: dict to update with new reachability information, as a
            map from chain ID to max sequence number reachable.
+        backwards: If True, walks backwards down the chains. If False, walks forwards from the chains.
    """

    # Do a standard graph traversal.
@@ -2195,12 +2442,104 @@ def _materialize(
            target_chain_id,
            target_sequence_number,
        ) in chain_links:
-            # Ignore any links that are higher up the chain
-            if sequence_number > s:
-                continue
+            if backwards:
+                # Ignore any links that are higher up the chain
+                if sequence_number > s:
+                    continue

-            # Check if we have already visited the target chain before, if so we
-            # can skip it.
-            if materialized.get(target_chain_id, 0) < target_sequence_number:
-                stack.append((target_chain_id, target_sequence_number))
-                materialized[target_chain_id] = target_sequence_number
+                # Check if we have already visited the target chain before, if so we
+                # can skip it.
+                if materialized.get(target_chain_id, 0) < target_sequence_number:
+                    stack.append((target_chain_id, target_sequence_number))
+                    materialized[target_chain_id] = target_sequence_number
+            else:
+                # Ignore any links that are lower down the chain.
+                if sequence_number < s:
+                    continue
+                # Check if we have already visited the target chain before, if so we
+                # can skip it.
+                if (
+                    materialized.get(target_chain_id, MAX_CHAIN_LENGTH)
+                    > target_sequence_number
+                ):
+                    stack.append((target_chain_id, target_sequence_number))
+                    materialized[target_chain_id] = target_sequence_number
+
+
+def _generate_forward_links(
+    links: Dict[int, List[Tuple[int, int, int]]],
+) -> Dict[int, List[Tuple[int, int, int]]]:
+    """Reverse the input links from the given backwards links"""
+    new_links: Dict[int, List[Tuple[int, int, int]]] = {}
+    for origin_chain_id, chain_links in links.items():
+        for origin_seq_num, target_chain_id, target_seq_num in chain_links:
+            new_links.setdefault(target_chain_id, []).append(
+                (target_seq_num, origin_chain_id, origin_seq_num)
+            )
+    return new_links
+
+
+def accumulate_forwards_reachable_events(
+    conflicted_forwards_reachable: Dict[int, int],
+    back_links: Dict[int, List[Tuple[int, int, int]]],
+    conflicted_chain_positions: Dict[str, Tuple[int, int]],
+) -> None:
+    """Accumulate new forwards reachable events using the back_links provided.
+
+    Accumulating forwards reachable information is quite different from backwards reachable information
+    because _get_chain_links returns the entire linkage information for backwards reachable events,
+    but not _forwards_ reachable events. We are only interested in the forwards reachable information
+    that is encoded in the backwards reachable links, so we can just invert all the operations we do
+    for backwards reachable events to calculate a subset of forwards reachable information. The
+    caveat with this approach is that it is a _subset_. This means new back_links may encode new
+    forwards reachable information which we also need. Consider this scenario:
+
+    A <-- B <-- C <--- D <-- E <-- F         Chain 1
+                |
+                `----- G <-- H <-- I         Chain 2
+                             |
+                             `---- J <-- K   Chain 3
+
+    Now consider what happens when B is a conflicted event. _get_chain_links returns the conflicted
+    chain and ALL links heading towards the root of the graph. This means we will know the
+    Chain 1 to Chain 2 link via C (as all links for the chain are returned, not strictly ones with
+    a lower sequence number), but we will NOT know the Chain 2 to Chain 3 link via H. We can be
+    blissfully unaware of Chain 3 entirely, if and only if there isn't some other conflicted event
+    on that chain. Consider what happens when K is /also/ conflicted. _get_chain_links will generate
+    two iterations: one for B and one for K. It's important that we re-evaluate the forwards reachable
+    information for B to include Chain 3 when we process the K iteration, hence we are "accumulating"
+    forwards reachability information.
+
+    NB: We don't consider 'additional backwards reachable events' here because they have no effect
+    on forwards reachability calculations, only backwards.
+
+    Args:
+      conflicted_forwards_reachable: The materialised dict of forwards reachable information.
+      The output to this function are stored here.
+      back_links: One iteration of _get_chain_links which encodes backwards reachable information.
+      conflicted_chain_positions: The conflicted events.
+    """
+    # links go backwards but we want them to go forwards as well for v2.1
+    fwd_links = _generate_forward_links(back_links)
+
+    # for each conflicted event, accumulate forwards reachability information
+    for (
+        conflicted_chain_id,
+        conflicted_chain_seq,
+    ) in conflicted_chain_positions.values():
+        # the conflicted event itself encodes reachability information
+        # e.g if D was conflicted, it encodes E,F as forwards reachable.
+        conflicted_forwards_reachable[conflicted_chain_id] = min(
+            conflicted_chain_seq,
+            conflicted_forwards_reachable.get(conflicted_chain_id, MAX_CHAIN_LENGTH),
+        )
+        # Walk from the conflicted event forwards to explore the links.
+        # This function checks if we've visited the chain before and skips reprocessing, so this
+        # does not repeatedly traverse the graph.
+        _materialize(
+            conflicted_chain_id,
+            conflicted_chain_seq,
+            fwd_links,
+            conflicted_forwards_reachable,
+            backwards=False,
+        )
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -51,7 +51,12 @@ from synapse.api.constants import (
 )
 from synapse.api.errors import PartialStateConflictError
 from synapse.api.room_versions import RoomVersions
-from synapse.events import EventBase, StrippedStateEvent, relation_from_event
+from synapse.events import (
+    EventBase,
+    StrippedStateEvent,
+    is_creator,
+    relation_from_event,
+)
 from synapse.events.snapshot import EventContext
 from synapse.events.utils import parse_stripped_state_event
 from synapse.logging.opentracing import trace
@@ -481,17 +486,27 @@ class PersistEventsStore:
        pl_id = state[(EventTypes.PowerLevels, "")]
        pl_event = await self.store.get_event(pl_id, allow_none=True)

-        if pl_event is None:
-            # per the spec, if a power level event isn't in the room, grant the creator
-            # level 100 and all other users 0
-            create_id = state[(EventTypes.Create, "")]
-            create_event = await self.store.get_event(create_id, allow_none=True)
-            if create_event is None:
-                # not sure how this would happen but if it does then just deny the redaction
-                logger.warning("No create event found for room %s", event.room_id)
-                return False
-            if create_event.sender == event.sender:
+        create_id = state[(EventTypes.Create, "")]
+        create_event = await self.store.get_event(create_id, allow_none=True)
+
+        if create_event is None:
+            # not sure how this would happen but if it does then just deny the redaction
+            logger.warning("No create event found for room %s", event.room_id)
+            return False
+
+        if create_event.room_version.msc4289_creator_power_enabled:
+            # per the spec, grant the creator infinite power level and all other users 0
+            if is_creator(create_event, event.sender):
                return True
+            if pl_event is None:
+                # per the spec, users other than the room creator have power level
+                # 0, which is less than the default to redact events (50).
+                return False
+        else:
+            # per the spec, if a power level event isn't in the room, grant the creator
+            # level 100 (the default redaction level is 50) and all other users 0
+            if pl_event is None:
+                return create_event.sender == event.sender

        assert pl_event is not None
        sender_level = pl_event.content.get("users", {}).get(event.sender)
--- a/synapse/storage/databases/main/purge_events.py
+++ b/synapse/storage/databases/main/purge_events.py
@@ -33,6 +33,73 @@ from synapse.types import RoomStreamToken
 logger = logging.getLogger(__name__)


+purge_room_tables_with_event_id_index = (
+    "event_auth",
+    "event_edges",
+    "event_json",
+    "event_push_actions_staging",
+    "event_relations",
+    "event_to_state_groups",
+    "event_auth_chains",
+    "event_auth_chain_to_calculate",
+    "redactions",
+    "rejections",
+    "state_events",
+)
+"""
+Tables which lack an index on `room_id` but have one on `event_id`
+"""
+
+purge_room_tables_with_room_id_column = (
+    "current_state_events",
+    "destination_rooms",
+    "event_backward_extremities",
+    "event_forward_extremities",
+    "event_push_actions",
+    "event_search",
+    "event_failed_pull_attempts",
+    # Note: the partial state tables have foreign keys between each other, and to
+    # `events` and `rooms`. We need to delete from them in the right order.
+    "partial_state_events",
+    "partial_state_rooms_servers",
+    "partial_state_rooms",
+    # Note: the _membership(s) tables have foreign keys to the `events` table
+    # so must be deleted first.
+    "local_current_membership",
+    "room_memberships",
+    # Note: the sliding_sync_ tables have foreign keys to the `events` table
+    # so must be deleted first.
+    "sliding_sync_joined_rooms",
+    "sliding_sync_membership_snapshots",
+    "events",
+    "federation_inbound_events_staging",
+    "receipts_graph",
+    "receipts_linearized",
+    "room_aliases",
+    "room_depth",
+    "room_stats_state",
+    "room_stats_current",
+    "room_stats_earliest_token",
+    "stream_ordering_to_exterm",
+    "users_in_public_rooms",
+    "users_who_share_private_rooms",
+    # no useful index, but let's clear them anyway
+    "appservice_room_list",
+    "e2e_room_keys",
+    "event_push_summary",
+    "pusher_throttle",
+    "room_account_data",
+    "room_tags",
+    # "rooms" happens last, to keep the foreign keys in the other tables
+    # happy
+    "rooms",
+)
+"""
+The tables with a `room_id` column regardless of whether they have a useful index on
+`room_id`.
+"""
+
+
 class PurgeEventsStore(StateGroupWorkerStore, CacheInvalidationWorkerStore):
    async def purge_history(
        self, room_id: str, token: str, delete_local_events: bool
@@ -398,20 +465,8 @@ class PurgeEventsStore(StateGroupWorkerStore, CacheInvalidationWorkerStore):
            referenced_chain_id_tuples,
        )

-        # Now we delete tables which lack an index on room_id but have one on event_id
-        for table in (
-            "event_auth",
-            "event_edges",
-            "event_json",
-            "event_push_actions_staging",
-            "event_relations",
-            "event_to_state_groups",
-            "event_auth_chains",
-            "event_auth_chain_to_calculate",
-            "redactions",
-            "rejections",
-            "state_events",
-        ):
+        # Now we delete tables which lack an index on `room_id` but have one on `event_id`
+        for table in purge_room_tables_with_event_id_index:
            logger.info("[purge] removing from %s", table)

            txn.execute(
@@ -424,51 +479,9 @@ class PurgeEventsStore(StateGroupWorkerStore, CacheInvalidationWorkerStore):
                (room_id,),
            )

-        # next, the tables with an index on room_id (or no useful index)
-        for table in (
-            "current_state_events",
-            "destination_rooms",
-            "event_backward_extremities",
-            "event_forward_extremities",
-            "event_push_actions",
-            "event_search",
-            "event_failed_pull_attempts",
-            # Note: the partial state tables have foreign keys between each other, and to
-            # `events` and `rooms`. We need to delete from them in the right order.
-            "partial_state_events",
-            "partial_state_rooms_servers",
-            "partial_state_rooms",
-            # Note: the _membership(s) tables have foreign keys to the `events` table
-            # so must be deleted first.
-            "local_current_membership",
-            "room_memberships",
-            # Note: the sliding_sync_ tables have foreign keys to the `events` table
-            # so must be deleted first.
-            "sliding_sync_joined_rooms",
-            "sliding_sync_membership_snapshots",
-            "events",
-            "federation_inbound_events_staging",
-            "receipts_graph",
-            "receipts_linearized",
-            "room_aliases",
-            "room_depth",
-            "room_stats_state",
-            "room_stats_current",
-            "room_stats_earliest_token",
-            "stream_ordering_to_exterm",
-            "users_in_public_rooms",
-            "users_who_share_private_rooms",
-            # no useful index, but let's clear them anyway
-            "appservice_room_list",
-            "e2e_room_keys",
-            "event_push_summary",
-            "pusher_throttle",
-            "room_account_data",
-            "room_tags",
-            # "rooms" happens last, to keep the foreign keys in the other tables
-            # happy
-            "rooms",
-        ):
+        # next, the tables with a `room_id` column regardless of whether they have a
+        # useful index on `room_id`
+        for table in purge_room_tables_with_room_id_column:
            logger.info("[purge] removing from %s", table)
            txn.execute("DELETE FROM %s WHERE room_id=?" % (table,), (room_id,))

--- a/synapse/storage/databases/main/roommember.py
+++ b/synapse/storage/databases/main/roommember.py
@@ -196,6 +196,19 @@ class RoomMemberWorkerStore(EventsWorkerStore, CacheInvalidationWorkerStore):
            retcol="state_key",
        )

+    async def get_invited_users_in_room(self, room_id: str) -> StrCollection:
+        """Returns a list of users invited to the room."""
+        return await self.db_pool.simple_select_onecol(
+            table="current_state_events",
+            keyvalues={
+                "type": EventTypes.Member,
+                "room_id": room_id,
+                "membership": Membership.INVITE,
+            },
+            retcol="state_key",
+            desc="get_invited_users_in_room",
+        )
+
    @cached()
    def get_user_in_room_with_profile(self, room_id: str, user_id: str) -> ProfileInfo:
        raise NotImplementedError()
--- a/synapse/types/init.py
+++ b/synapse/types/init.py
@@ -355,12 +355,78 @@ class RoomAlias(DomainSpecificString):


@attr.s(slots=True, frozen=True, repr=False)
-class RoomID(DomainSpecificString):
-    """Structure representing a room id."""
+class RoomIdWithDomain(DomainSpecificString):
+    """Structure representing a room ID with a domain suffix."""

    SIGIL = "!"


+# the set of urlsafe base64 characters, no padding.
+ROOM_ID_PATTERN_DOMAINLESS = re.compile(r"^[A-Za-z0-9\-_]{43}$")
+
+
+@attr.s(slots=True, frozen=True, auto_attribs=True, repr=False)
+class RoomID:
+    """Structure representing a room id without a domain.
+    There are two forms of room IDs:
+      - "!localpart:domain" used in most room versions prior to MSC4291.
+      - "!event_id_base_64" used in room versions post MSC4291.
+    This class will accept any room ID which meets either of these two criteria.
+    """
+
+    SIGIL = "!"
+    id: str
+    room_id_with_domain: Optional[RoomIdWithDomain]
+
+    @classmethod
+    def is_valid(cls: Type["RoomID"], s: str) -> bool:
+        if ":" in s:
+            return RoomIdWithDomain.is_valid(s)
+        try:
+            cls.from_string(s)
+            return True
+        except Exception:
+            return False
+
+    def get_domain(self) -> Optional[str]:
+        if not self.room_id_with_domain:
+            return None
+        return self.room_id_with_domain.domain
+
+    def to_string(self) -> str:
+        if self.room_id_with_domain:
+            return self.room_id_with_domain.to_string()
+        return self.id
+
+    __repr__ = to_string
+
+    @classmethod
+    def from_string(cls: Type["RoomID"], s: str) -> "RoomID":
+        # sigil check
+        if len(s) < 1 or s[0] != cls.SIGIL:
+            raise SynapseError(
+                400,
+                "Expected %s string to start with '%s'" % (cls.__name__, cls.SIGIL),
+                Codes.INVALID_PARAM,
+            )
+
+        room_id_with_domain: Optional[RoomIdWithDomain] = None
+        if ":" in s:
+            room_id_with_domain = RoomIdWithDomain.from_string(s)
+        else:
+            # MSC4291 room IDs must be valid urlsafe unpadded base64
+            val = s[1:]
+            if not ROOM_ID_PATTERN_DOMAINLESS.match(val):
+                raise SynapseError(
+                    400,
+                    "Expected %s string to be valid urlsafe unpadded base64 '%s'"
+                    % (cls.__name__, val),
+                    Codes.INVALID_PARAM,
+                )
+
+        return cls(id=s, room_id_with_domain=room_id_with_domain)
+
+
@attr.s(slots=True, frozen=True, repr=False)
 class EventID(DomainSpecificString):
    """Structure representing an event ID which is namespaced to a homeserver.
--- a/tests/rest/admin/test_room.py
+++ b/tests/rest/admin/test_room.py
@@ -33,12 +33,17 @@ from twisted.internet.testing import MemoryReactor
 import synapse.rest.admin
 from synapse.api.constants import EventTypes, Membership, RoomTypes
 from synapse.api.errors import Codes
+from synapse.api.room_versions import RoomVersions
 from synapse.handlers.pagination import (
    PURGE_ROOM_ACTION_NAME,
    SHUTDOWN_AND_PURGE_ROOM_ACTION_NAME,
 )
 from synapse.rest.client import directory, events, knock, login, room, sync
 from synapse.server import HomeServer
+from synapse.storage.databases.main.purge_events import (
+    purge_room_tables_with_event_id_index,
+    purge_room_tables_with_room_id_column,
+)
 from synapse.types import UserID
 from synapse.util import Clock
 from synapse.util.task_scheduler import TaskScheduler
@@ -546,7 +551,7 @@ class DeleteRoomTestCase(unittest.HomeserverTestCase):

    def _is_purged(self, room_id: str) -> None:
        """Test that the following tables have been purged of all rows related to the room."""
-        for table in PURGE_TABLES:
+        for table in purge_room_tables_with_room_id_column:
            count = self.get_success(
                self.store.db_pool.simple_select_one_onecol(
                    table=table,
@@ -555,7 +560,21 @@ class DeleteRoomTestCase(unittest.HomeserverTestCase):
                    desc="test_purge_room",
                )
            )
+            self.assertEqual(count, 0, msg=f"Rows not purged in {table}")

+        for table in purge_room_tables_with_event_id_index:
+            rows = self.get_success(
+                self.store.db_pool.execute(
+                    "find_event_count_for_table",
+                    f"""
+                    SELECT COUNT(*) FROM {table} WHERE event_id IN (
+                        SELECT event_id FROM events WHERE room_id=?
+                    )
+                    """,
+                    room_id,
+                )
+            )
+            count = rows[0][0]
            self.assertEqual(count, 0, msg=f"Rows not purged in {table}")

    def _assert_peek(self, room_id: str, expect_code: int) -> None:
@@ -1228,7 +1247,7 @@ class DeleteRoomV2TestCase(unittest.HomeserverTestCase):

    def _is_purged(self, room_id: str) -> None:
        """Test that the following tables have been purged of all rows related to the room."""
-        for table in PURGE_TABLES:
+        for table in purge_room_tables_with_room_id_column:
            count = self.get_success(
                self.store.db_pool.simple_select_one_onecol(
                    table=table,
@@ -1237,7 +1256,21 @@ class DeleteRoomV2TestCase(unittest.HomeserverTestCase):
                    desc="test_purge_room",
                )
            )
+            self.assertEqual(count, 0, msg=f"Rows not purged in {table}")

+        for table in purge_room_tables_with_event_id_index:
+            rows = self.get_success(
+                self.store.db_pool.execute(
+                    "find_event_count_for_table",
+                    f"""
+                    SELECT COUNT(*) FROM {table} WHERE event_id IN (
+                        SELECT event_id FROM events WHERE room_id=?
+                    )
+                    """,
+                    room_id,
+                )
+            )
+            count = rows[0][0]
            self.assertEqual(count, 0, msg=f"Rows not purged in {table}")

    def _assert_peek(self, room_id: str, expect_code: int) -> None:
@@ -2892,6 +2925,63 @@ class MakeRoomAdminTestCase(unittest.HomeserverTestCase):
            "No local admin user in room with power to update power levels.",
        )

+    def test_v12_room(self) -> None:
+        """Test that you can be promoted to admin in v12 rooms which won't have the admin the PL event."""
+        room_id = self.helper.create_room_as(
+            self.creator,
+            tok=self.creator_tok,
+            room_version=RoomVersions.V12.identifier,
+        )
+
+        channel = self.make_request(
+            "POST",
+            f"/_synapse/admin/v1/rooms/{room_id}/make_room_admin",
+            content={},
+            access_token=self.admin_user_tok,
+        )
+
+        self.assertEqual(200, channel.code, msg=channel.json_body)
+
+        # Now we test that we can join the room and that the admin user has PL 100.
+        self.helper.join(room_id, self.admin_user, tok=self.admin_user_tok)
+        pl = self.helper.get_state(
+            room_id, EventTypes.PowerLevels, tok=self.creator_tok
+        )
+        self.assertEquals(pl["users"][self.admin_user], 100)
+
+    def test_v12_room_with_many_user_pls(self) -> None:
+        """Test that you can be promoted to the admin user's PL in v12 rooms that contain a range of user PLs."""
+        room_id = self.helper.create_room_as(
+            self.creator,
+            tok=self.creator_tok,
+            room_version=RoomVersions.V12.identifier,
+            is_public=True,
+            extra_content={
+                "power_level_content_override": {
+                    "users": {
+                        self.second_user_id: 50,
+                    },
+                },
+            },
+        )
+
+        self.helper.join(room_id, self.admin_user, tok=self.admin_user_tok)
+        self.helper.join(room_id, self.second_user_id, tok=self.second_tok)
+
+        channel = self.make_request(
+            "POST",
+            f"/_synapse/admin/v1/rooms/{room_id}/make_room_admin",
+            content={},
+            access_token=self.admin_user_tok,
+        )
+
+        self.assertEqual(200, channel.code, msg=channel.json_body)
+
+        pl = self.helper.get_state(
+            room_id, EventTypes.PowerLevels, tok=self.creator_tok
+        )
+        self.assertEquals(pl["users"][self.admin_user], 100)
+

 class BlockRoomTestCase(unittest.HomeserverTestCase):
    servlets = [
@@ -3119,35 +3209,3 @@ class BlockRoomTestCase(unittest.HomeserverTestCase):
        """Block a room in database"""
        self.get_success(self._store.block_room(room_id, self.other_user))
        self._is_blocked(room_id, expect=True)
-
-
-PURGE_TABLES = [
-    "current_state_events",
-    "event_backward_extremities",
-    "event_forward_extremities",
-    "event_json",
-    "event_push_actions",
-    "event_search",
-    "events",
-    "receipts_graph",
-    "receipts_linearized",
-    "room_aliases",
-    "room_depth",
-    "room_memberships",
-    "room_stats_state",
-    "room_stats_current",
-    "room_stats_earliest_token",
-    "rooms",
-    "stream_ordering_to_exterm",
-    "users_in_public_rooms",
-    "users_who_share_private_rooms",
-    "appservice_room_list",
-    "e2e_room_keys",
-    "event_push_summary",
-    "pusher_throttle",
-    "room_account_data",
-    "room_tags",
-    "state_groups",
-    "state_groups_state",
-    "federation_inbound_events_staging",
-]
--- a/tests/state/test_v2.py
+++ b/tests/state/test_v2.py
@@ -45,6 +45,7 @@ from synapse.state.v2 import (
    lexicographical_topological_sort,
    resolve_events_with_store,
 )
+from synapse.storage.databases.main.event_federation import StateDifference
 from synapse.types import EventID, StateMap

 from tests import unittest
@@ -734,7 +735,11 @@ class AuthChainDifferenceTestCase(unittest.TestCase):
        store = TestStateResolutionStore(persisted_events)

        diff_d = _get_auth_chain_difference(
-            ROOM_ID, state_sets, unpersited_events, store
+            ROOM_ID,
+            state_sets,
+            unpersited_events,
+            store,
+            None,
        )
        difference = self.successResultOf(defer.ensureDeferred(diff_d))

@@ -791,7 +796,11 @@ class AuthChainDifferenceTestCase(unittest.TestCase):
        store = TestStateResolutionStore(persisted_events)

        diff_d = _get_auth_chain_difference(
-            ROOM_ID, state_sets, unpersited_events, store
+            ROOM_ID,
+            state_sets,
+            unpersited_events,
+            store,
+            None,
        )
        difference = self.successResultOf(defer.ensureDeferred(diff_d))

@@ -858,7 +867,11 @@ class AuthChainDifferenceTestCase(unittest.TestCase):
        store = TestStateResolutionStore(persisted_events)

        diff_d = _get_auth_chain_difference(
-            ROOM_ID, state_sets, unpersited_events, store
+            ROOM_ID,
+            state_sets,
+            unpersited_events,
+            store,
+            None,
        )
        difference = self.successResultOf(defer.ensureDeferred(diff_d))

@@ -1070,9 +1083,18 @@ class TestStateResolutionStore:
        return list(result)

    def get_auth_chain_difference(
-        self, room_id: str, auth_sets: List[Set[str]]
-    ) -> "defer.Deferred[Set[str]]":
+        self,
+        room_id: str,
+        auth_sets: List[Set[str]],
+        conflicted_state: Optional[Set[str]],
+        additional_backwards_reachable_conflicted_events: Optional[Set[str]],
+    ) -> "defer.Deferred[StateDifference]":
        chains = [frozenset(self._get_auth_chain(a)) for a in auth_sets]

        common = set(chains[0]).intersection(*chains[1:])
-        return defer.succeed(set(chains[0]).union(*chains[1:]) - common)
+        return defer.succeed(
+            StateDifference(
+                auth_difference=set(chains[0]).union(*chains[1:]) - common,
+                conflicted_subgraph=set(),
+            ),
+        )
--- a/tests/state/test_v21.py
+++ b/tests/state/test_v21.py
@@ -0,0 +1,505 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2025 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+# Originally licensed under the Apache License, Version 2.0:
+# <http://www.apache.org/licenses/LICENSE-2.0>.
+#
+# [This file includes modifications made by New Vector Limited]
+#
+#
+import itertools
+from typing import Dict, List, Optional, Sequence, Set
+
+from twisted.internet import defer
+from twisted.test.proto_helpers import MemoryReactor
+
+from synapse.api.constants import EventTypes, JoinRules, Membership
+from synapse.api.room_versions import RoomVersions
+from synapse.events import EventBase
+from synapse.federation.federation_base import event_from_pdu_json
+from synapse.rest import admin
+from synapse.rest.client import login, room
+from synapse.server import HomeServer
+from synapse.state import StateResolutionStore
+from synapse.state.v2 import (
+    StateResolutionStore as StateResolutionStoreInterface,
+    _get_auth_chain_difference,
+    _seperate,
+    resolve_events_with_store,
+)
+from synapse.types import StateMap
+from synapse.util import Clock
+
+from tests import unittest
+from tests.state.test_v2 import TestStateResolutionStore
+
+ALICE = "@alice:example.com"
+BOB = "@bob:example.com"
+CHARLIE = "@charlie:example.com"
+EVELYN = "@evelyn:example.com"
+ZARA = "@zara:example.com"
+
+ROOM_ID = "!test:example.com"
+
+MEMBERSHIP_CONTENT_JOIN = {"membership": Membership.JOIN}
+MEMBERSHIP_CONTENT_INVITE = {"membership": Membership.INVITE}
+MEMBERSHIP_CONTENT_LEAVE = {"membership": Membership.LEAVE}
+
+
+ORIGIN_SERVER_TS = 0
+
+
+def monotonic_timestamp() -> int:
+    global ORIGIN_SERVER_TS
+    ORIGIN_SERVER_TS += 1
+    return ORIGIN_SERVER_TS
+
+
+class FakeClock:
+    async def sleep(self, duration_ms: float) -> None:
+        defer.succeed(None)
+
+
+class StateResV21TestCase(unittest.HomeserverTestCase):
+    servlets = [
+        admin.register_servlets,
+        room.register_servlets,
+        login.register_servlets,
+    ]
+
+    def prepare(
+        self, reactor: MemoryReactor, clock: Clock, homeserver: HomeServer
+    ) -> None:
+        self.state = self.hs.get_state_handler()
+        persistence = self.hs.get_storage_controllers().persistence
+        assert persistence is not None
+        self._persistence = persistence
+        self._state_storage_controller = self.hs.get_storage_controllers().state
+        self._state_deletion = self.hs.get_datastores().state_deletion
+        self.store = self.hs.get_datastores().main
+
+        self.register_user("user", "pass")
+        self.token = self.login("user", "pass")
+
+    def test_state_reset_replay_conflicted_subgraph(self) -> None:
+        # 1. Alice creates a room.
+        e1_create = self.create_event(
+            EventTypes.Create,
+            "",
+            sender=ALICE,
+            content={"creator": ALICE},
+            auth_events=[],
+        )
+        # 2. Alice joins it.
+        e2_ma = self.create_event(
+            EventTypes.Member,
+            ALICE,
+            sender=ALICE,
+            content=MEMBERSHIP_CONTENT_JOIN,
+            auth_events=[],
+            prev_events=[e1_create.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 3. Alice is the creator
+        e3_power1 = self.create_event(
+            EventTypes.PowerLevels,
+            "",
+            sender=ALICE,
+            content={"users": {}},
+            auth_events=[e2_ma.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 4. Alice sets the room to public.
+        e4_jr = self.create_event(
+            EventTypes.JoinRules,
+            "",
+            sender=ALICE,
+            content={"join_rule": JoinRules.PUBLIC},
+            auth_events=[e2_ma.event_id, e3_power1.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 5. Bob joins the room.
+        e5_mb = self.create_event(
+            EventTypes.Member,
+            BOB,
+            sender=BOB,
+            content=MEMBERSHIP_CONTENT_JOIN,
+            auth_events=[e3_power1.event_id, e4_jr.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 6. Charlie joins the room.
+        e6_mc = self.create_event(
+            EventTypes.Member,
+            CHARLIE,
+            sender=CHARLIE,
+            content=MEMBERSHIP_CONTENT_JOIN,
+            auth_events=[e3_power1.event_id, e4_jr.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 7. Alice promotes Bob.
+        e7_power2 = self.create_event(
+            EventTypes.PowerLevels,
+            "",
+            sender=ALICE,
+            content={"users": {BOB: 50}},
+            auth_events=[e2_ma.event_id, e3_power1.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 8. Bob promotes Charlie.
+        e8_power3 = self.create_event(
+            EventTypes.PowerLevels,
+            "",
+            sender=BOB,
+            content={"users": {BOB: 50, CHARLIE: 50}},
+            auth_events=[e5_mb.event_id, e7_power2.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 9. Eve joins the room.
+        e9_me1 = self.create_event(
+            EventTypes.Member,
+            EVELYN,
+            sender=EVELYN,
+            content=MEMBERSHIP_CONTENT_JOIN,
+            auth_events=[e8_power3.event_id, e4_jr.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 10. Eve changes her name, /!\\ but cites old power levels /!\
+        e10_me2 = self.create_event(
+            EventTypes.Member,
+            EVELYN,
+            sender=EVELYN,
+            content=MEMBERSHIP_CONTENT_JOIN,
+            auth_events=[
+                e3_power1.event_id,
+                e4_jr.event_id,
+                e9_me1.event_id,
+            ],
+            room_id=e1_create.room_id,
+        )
+        # 11. Zara joins the room, citing the most recent power levels.
+        e11_mz = self.create_event(
+            EventTypes.Member,
+            ZARA,
+            sender=ZARA,
+            content=MEMBERSHIP_CONTENT_JOIN,
+            auth_events=[e8_power3.event_id, e4_jr.event_id],
+            room_id=e1_create.room_id,
+        )
+
+        # Event 10 above is DODGY: it directly cites old auth events, but indirectly
+        # cites new ones. If the state after event 10 contains old power level and old
+        # join events, we are vulnerable to a reset.
+
+        dodgy_state_after_eve_rename: StateMap[str] = {
+            (EventTypes.Create, ""): e1_create.event_id,
+            (EventTypes.Member, ALICE): e2_ma.event_id,
+            (EventTypes.Member, BOB): e5_mb.event_id,
+            (EventTypes.Member, CHARLIE): e6_mc.event_id,
+            (EventTypes.Member, EVELYN): e10_me2.event_id,
+            (EventTypes.PowerLevels, ""): e3_power1.event_id,  # old and /!\\ DODGY /!\
+            (EventTypes.JoinRules, ""): e4_jr.event_id,
+        }
+
+        sensible_state_after_zara_joins: StateMap[str] = {
+            (EventTypes.Create, ""): e1_create.event_id,
+            (EventTypes.Member, ALICE): e2_ma.event_id,
+            (EventTypes.Member, BOB): e5_mb.event_id,
+            (EventTypes.Member, CHARLIE): e6_mc.event_id,
+            (EventTypes.Member, ZARA): e11_mz.event_id,
+            (EventTypes.PowerLevels, ""): e8_power3.event_id,
+            (EventTypes.JoinRules, ""): e4_jr.event_id,
+        }
+
+        expected: StateMap[str] = {
+            (EventTypes.Create, ""): e1_create.event_id,
+            (EventTypes.Member, ALICE): e2_ma.event_id,
+            (EventTypes.Member, BOB): e5_mb.event_id,
+            (EventTypes.Member, CHARLIE): e6_mc.event_id,
+            # Expect ME2 replayed first: it's in the POWER 1 epoch
+            # Then ME1, in the POWER 3 epoch
+            (EventTypes.Member, EVELYN): e9_me1.event_id,
+            (EventTypes.Member, ZARA): e11_mz.event_id,
+            (EventTypes.PowerLevels, ""): e8_power3.event_id,
+            (EventTypes.JoinRules, ""): e4_jr.event_id,
+        }
+
+        self.get_resolution_and_verify_expected(
+            [dodgy_state_after_eve_rename, sensible_state_after_zara_joins],
+            [
+                e1_create,
+                e2_ma,
+                e3_power1,
+                e4_jr,
+                e5_mb,
+                e6_mc,
+                e7_power2,
+                e8_power3,
+                e9_me1,
+                e10_me2,
+                e11_mz,
+            ],
+            expected,
+        )
+
+    def test_state_reset_start_empty_set(self) -> None:
+        # The join rules reset to missing, when:
+        # - join rules were in conflict
+        # - the membership of those join rules' senders were not in conflict
+        # - those memberships are all leaves.
+
+        # 1. Alice creates a room.
+        e1_create = self.create_event(
+            EventTypes.Create,
+            "",
+            sender=ALICE,
+            content={"creator": ALICE},
+            auth_events=[],
+        )
+        # 2. Alice joins it.
+        e2_ma1 = self.create_event(
+            EventTypes.Member,
+            ALICE,
+            sender=ALICE,
+            content=MEMBERSHIP_CONTENT_JOIN,
+            auth_events=[],
+            room_id=e1_create.room_id,
+        )
+        # 3. Alice makes Bob an admin.
+        e3_power = self.create_event(
+            EventTypes.PowerLevels,
+            "",
+            sender=ALICE,
+            content={"users": {BOB: 100}},
+            auth_events=[e2_ma1.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 4. Alice sets the room to public.
+        e4_jr1 = self.create_event(
+            EventTypes.JoinRules,
+            "",
+            sender=ALICE,
+            content={"join_rule": JoinRules.PUBLIC},
+            auth_events=[e2_ma1.event_id, e3_power.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 5. Bob joins.
+        e5_mb = self.create_event(
+            EventTypes.Member,
+            BOB,
+            sender=BOB,
+            content=MEMBERSHIP_CONTENT_JOIN,
+            auth_events=[e3_power.event_id, e4_jr1.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 6. Alice sets join rules to invite.
+        e6_jr2 = self.create_event(
+            EventTypes.JoinRules,
+            "",
+            sender=ALICE,
+            content={"join_rule": JoinRules.INVITE},
+            auth_events=[e2_ma1.event_id, e3_power.event_id],
+            room_id=e1_create.room_id,
+        )
+        # 7. Alice then leaves.
+        e7_ma2 = self.create_event(
+            EventTypes.Member,
+            ALICE,
+            sender=ALICE,
+            content=MEMBERSHIP_CONTENT_LEAVE,
+            auth_events=[e3_power.event_id, e2_ma1.event_id],
+            room_id=e1_create.room_id,
+        )
+
+        correct_state: StateMap[str] = {
+            (EventTypes.Create, ""): e1_create.event_id,
+            (EventTypes.Member, ALICE): e7_ma2.event_id,
+            (EventTypes.Member, BOB): e5_mb.event_id,
+            (EventTypes.PowerLevels, ""): e3_power.event_id,
+            (EventTypes.JoinRules, ""): e6_jr2.event_id,
+        }
+
+        # Imagine that another server gives us incorrect state on a fork
+        # (via e.g. backfill). It cites the old join rules.
+        incorrect_state: StateMap[str] = {
+            (EventTypes.Create, ""): e1_create.event_id,
+            (EventTypes.Member, ALICE): e7_ma2.event_id,
+            (EventTypes.Member, BOB): e5_mb.event_id,
+            (EventTypes.PowerLevels, ""): e3_power.event_id,
+            (EventTypes.JoinRules, ""): e4_jr1.event_id,
+        }
+
+        # Resolving those two should give us the new join rules.
+        expected: StateMap[str] = {
+            (EventTypes.Create, ""): e1_create.event_id,
+            (EventTypes.Member, ALICE): e7_ma2.event_id,
+            (EventTypes.Member, BOB): e5_mb.event_id,
+            (EventTypes.PowerLevels, ""): e3_power.event_id,
+            (EventTypes.JoinRules, ""): e6_jr2.event_id,
+        }
+
+        self.get_resolution_and_verify_expected(
+            [correct_state, incorrect_state],
+            [e1_create, e2_ma1, e3_power, e4_jr1, e5_mb, e6_jr2, e7_ma2],
+            expected,
+        )
+
+    async def _get_auth_difference_and_conflicted_subgraph(
+        self,
+        room_id: str,
+        state_maps: Sequence[StateMap[str]],
+        event_map: Optional[Dict[str, EventBase]],
+        state_res_store: StateResolutionStoreInterface,
+    ) -> Set[str]:
+        _, conflicted_state = _seperate(state_maps)
+        conflicted_set: Optional[Set[str]] = set(
+            itertools.chain.from_iterable(conflicted_state.values())
+        )
+        if event_map is None:
+            event_map = {}
+        return await _get_auth_chain_difference(
+            room_id,
+            state_maps,
+            event_map,
+            state_res_store,
+            conflicted_set,
+        )
+
+    def get_resolution_and_verify_expected(
+        self,
+        state_maps: Sequence[StateMap[str]],
+        events: List[EventBase],
+        expected: StateMap[str],
+    ) -> None:
+        room_id = events[0].room_id
+        # First we try everything in-memory to check that the test case works.
+        event_map = {ev.event_id: ev for ev in events}
+        for ev in events:
+            print(f"{ev.event_id} => {ev.type} {ev.state_key} => {ev.content}")
+        resolution = self.get_success(
+            resolve_events_with_store(
+                FakeClock(),
+                room_id,
+                events[0].room_version,
+                state_maps,
+                event_map=event_map,
+                state_res_store=TestStateResolutionStore(event_map),
+            )
+        )
+        self.assertEqual(resolution, expected)
+
+        got_auth_diff = self.get_success(
+            self._get_auth_difference_and_conflicted_subgraph(
+                room_id,
+                state_maps,
+                event_map,
+                TestStateResolutionStore(event_map),
+            )
+        )
+        # we should never see the create event in the auth diff. If we do, this implies the
+        # conflicted subgraph is wrong and is returning too many old events.
+        assert events[0].event_id not in got_auth_diff
+
+        # now let's make the room exist on the DB, some queries rely on there being a row in
+        # the rooms table when persisting
+        self.get_success(
+            self.store.store_room(
+                room_id,
+                events[0].sender,
+                True,
+                events[0].room_version,
+            )
+        )
+
+        def resolve_and_check() -> None:
+            event_map = {ev.event_id: ev for ev in events}
+            store = StateResolutionStore(
+                self._persistence.main_store,
+                self._state_deletion,
+            )
+            resolution = self.get_success(
+                resolve_events_with_store(
+                    FakeClock(),
+                    room_id,
+                    RoomVersions.HydraV11,
+                    state_maps,
+                    event_map=event_map,
+                    state_res_store=store,
+                )
+            )
+            self.assertEqual(resolution, expected)
+            got_auth_diff2 = self.get_success(
+                self._get_auth_difference_and_conflicted_subgraph(
+                    room_id,
+                    state_maps,
+                    event_map,
+                    store,
+                )
+            )
+            # no matter how many events are persisted, the overall diff should always be the same.
+            self.assertEquals(got_auth_diff, got_auth_diff2)
+
+        # now we will drip feed in `events` one-by-one, persisting them then resolving with the
+        # rest. This ensures we correctly handle mixed persisted/unpersisted events. We will finish
+        # with doing the test with all persisted events.
+        while len(events) > 0:
+            event_to_persist = events.pop(0)
+            self.persist_event(event_to_persist)
+            # now retest
+            resolve_and_check()
+
+    def persist_event(
+        self, event: EventBase, state: Optional[StateMap[str]] = None
+    ) -> None:
+        """Persist the event, with optional state"""
+        context = self.get_success(
+            self.state.compute_event_context(
+                event,
+                state_ids_before_event=state,
+                partial_state=None if state is None else False,
+            )
+        )
+        self.get_success(self._persistence.persist_event(event, context))
+
+    def create_event(
+        self,
+        event_type: str,
+        state_key: Optional[str],
+        sender: str,
+        content: Dict,
+        auth_events: List[str],
+        prev_events: Optional[List[str]] = None,
+        room_id: Optional[str] = None,
+    ) -> EventBase:
+        """Short-hand for event_from_pdu_json for fields we typically care about.
+        Tests can override by just calling event_from_pdu_json directly."""
+        if prev_events is None:
+            prev_events = []
+
+        pdu = {
+            "type": event_type,
+            "state_key": state_key,
+            "content": content,
+            "sender": sender,
+            "depth": 5,
+            "prev_events": prev_events,
+            "auth_events": auth_events,
+            "origin_server_ts": monotonic_timestamp(),
+        }
+        if event_type != EventTypes.Create:
+            if room_id is None:
+                raise Exception("must specify a room_id to create_event")
+            pdu["room_id"] = room_id
+        return event_from_pdu_json(
+            pdu,
+            RoomVersions.HydraV11,
+        )
--- a/tests/storage/test_event_federation.py
+++ b/tests/storage/test_event_federation.py
@@ -26,6 +26,7 @@ from typing import (
    Iterable,
    List,
    Mapping,
+    NamedTuple,
    Set,
    Tuple,
    TypeVar,
@@ -730,6 +731,202 @@ class EventFederationWorkerStoreTestCase(tests.unittest.HomeserverTestCase):
        )
        self.assertSetEqual(difference, set())

+    def test_conflicted_subgraph(self) -> None:
+        """Test that the conflicted subgraph code in state res v2.1 can walk arbitrary length links
+        and chains.
+
+        We construct a chain cover index like this:
+
+        A1 <- A2 <- A3
+               ^--- B1 <- B2 <- B3
+                           ^--- C1 <- C2 <- C3     v--- G1 <- G2
+                                 ^--- D1 <- D2 <- D3
+                                             ^--- E1
+                                                   ^--- F1 <- F2
+
+        ..and then pick various events to be conflicted / additional backwards reachable to assert
+        that the code walks the chains correctly. We're particularly interested in ensuring that
+        the code walks multiple links between chains, hence why we have so many chains.
+        """
+
+        class TestNode(NamedTuple):
+            event_id: str
+            chain_id: int
+            seq_num: int
+
+        class TestLink(NamedTuple):
+            origin_chain_and_seq: Tuple[int, int]
+            target_chain_and_seq: Tuple[int, int]
+
+        # Map to chain IDs / seq nums
+        nodes: List[TestNode] = [
+            TestNode("A1", 1, 1),
+            TestNode("A2", 1, 2),
+            TestNode("A3", 1, 3),
+            TestNode("B1", 2, 1),
+            TestNode("B2", 2, 2),
+            TestNode("B3", 2, 3),
+            TestNode("C1", 3, 1),
+            TestNode("C2", 3, 2),
+            TestNode("C3", 3, 3),
+            TestNode("D1", 4, 1),
+            TestNode("D2", 4, 2),
+            TestNode("D3", 4, 3),
+            TestNode("E1", 5, 1),
+            TestNode("F1", 6, 1),
+            TestNode("F2", 6, 2),
+            TestNode("G1", 7, 1),
+            TestNode("G2", 7, 2),
+        ]
+        links: List[TestLink] = [
+            TestLink((2, 1), (1, 2)),  # B1 -> A2
+            TestLink((3, 1), (2, 2)),  # C1 -> B2
+            TestLink((4, 1), (3, 1)),  # D1 -> C1
+            TestLink((5, 1), (4, 2)),  # E1 -> D2
+            TestLink((6, 1), (5, 1)),  # F1 -> E1
+            TestLink((7, 1), (4, 3)),  # G1 -> D3
+        ]
+
+        # populate the chain cover index tables as that's all we need
+        for node in nodes:
+            self.get_success(
+                self.store.db_pool.simple_insert(
+                    "event_auth_chains",
+                    {
+                        "event_id": node.event_id,
+                        "chain_id": node.chain_id,
+                        "sequence_number": node.seq_num,
+                    },
+                    desc="insert",
+                )
+            )
+        for link in links:
+            self.get_success(
+                self.store.db_pool.simple_insert(
+                    "event_auth_chain_links",
+                    {
+                        "origin_chain_id": link.origin_chain_and_seq[0],
+                        "origin_sequence_number": link.origin_chain_and_seq[1],
+                        "target_chain_id": link.target_chain_and_seq[0],
+                        "target_sequence_number": link.target_chain_and_seq[1],
+                    },
+                    desc="insert",
+                )
+            )
+
+        # Define the test cases
+        class TestCase(NamedTuple):
+            name: str
+            conflicted: Set[str]
+            additional_backwards_reachable: Set[str]
+            want_conflicted_subgraph: Set[str]
+
+        # Reminder:
+        # A1 <- A2 <- A3
+        #        ^--- B1 <- B2 <- B3
+        #                    ^--- C1 <- C2 <- C3     v--- G1 <- G2
+        #                          ^--- D1 <- D2 <- D3
+        #                                      ^--- E1
+        #                                            ^--- F1 <- F2
+        test_cases = [
+            TestCase(
+                name="basic_single_chain",
+                conflicted={"B1", "B3"},
+                additional_backwards_reachable=set(),
+                want_conflicted_subgraph={"B1", "B2", "B3"},
+            ),
+            TestCase(
+                name="basic_single_link",
+                conflicted={"A1", "B2"},
+                additional_backwards_reachable=set(),
+                want_conflicted_subgraph={"A1", "A2", "B1", "B2"},
+            ),
+            TestCase(
+                name="basic_multi_link",
+                conflicted={"B1", "F1"},
+                additional_backwards_reachable=set(),
+                want_conflicted_subgraph={"B1", "B2", "C1", "D1", "D2", "E1", "F1"},
+            ),
+            # Repeat these tests but put the later event as an additional backwards reachable event.
+            # The output should be the same.
+            TestCase(
+                name="basic_single_chain_as_additional",
+                conflicted={"B1"},
+                additional_backwards_reachable={"B3"},
+                want_conflicted_subgraph={"B1", "B2", "B3"},
+            ),
+            TestCase(
+                name="basic_single_link_as_additional",
+                conflicted={"A1"},
+                additional_backwards_reachable={"B2"},
+                want_conflicted_subgraph={"A1", "A2", "B1", "B2"},
+            ),
+            TestCase(
+                name="basic_multi_link_as_additional",
+                conflicted={"B1"},
+                additional_backwards_reachable={"F1"},
+                want_conflicted_subgraph={"B1", "B2", "C1", "D1", "D2", "E1", "F1"},
+            ),
+            TestCase(
+                name="mixed_multi_link",
+                conflicted={"D1", "F1"},
+                additional_backwards_reachable={"G1"},
+                want_conflicted_subgraph={"D1", "D2", "D3", "E1", "F1", "G1"},
+            ),
+            TestCase(
+                name="additional_backwards_doesnt_add_forwards_info",
+                conflicted={"C1", "C3"},
+                # This is on the path to the root but Chain C isn't forwards reachable so this doesn't
+                # change anything.
+                additional_backwards_reachable={"B1"},
+                want_conflicted_subgraph={"C1", "C2", "C3"},
+            ),
+            TestCase(
+                name="empty_subgraph",
+                conflicted={
+                    "B3",
+                    "C3",
+                },  # these can't reach each other going forwards, so the subgraph is empty
+                additional_backwards_reachable=set(),
+                want_conflicted_subgraph={"B3", "C3"},
+            ),
+            TestCase(
+                name="empty_subgraph_with_additional",
+                conflicted={"C1"},
+                # This is on the path to the root but Chain C isn't forwards reachable so this doesn't
+                # change anything.
+                additional_backwards_reachable={"B1"},
+                want_conflicted_subgraph={"C1"},
+            ),
+            TestCase(
+                name="empty_subgraph_single_conflict",
+                conflicted={"C1"},  # no subgraph can form as you need 2+
+                additional_backwards_reachable=set(),
+                want_conflicted_subgraph={"C1"},
+            ),
+        ]
+
+        def run_test(txn: LoggingTransaction, test_case: TestCase) -> None:
+            result = self.store._get_auth_chain_difference_using_cover_index_txn(
+                txn,
+                "!not_relevant",
+                [test_case.conflicted.union(test_case.additional_backwards_reachable)],
+                test_case.conflicted,
+                test_case.additional_backwards_reachable,
+            )
+            self.assertEquals(
+                result.conflicted_subgraph,
+                test_case.want_conflicted_subgraph,
+                f"{test_case.name} : conflicted subgraph mismatch",
+            )
+
+        for test_case in test_cases:
+            self.get_success(
+                self.store.db_pool.runInteraction(
+                    f"test_case_{test_case.name}", run_test, test_case
+                )
+            )
+
    @parameterized.expand(
        [(room_version,) for room_version in KNOWN_ROOM_VERSIONS.values()]
    )
--- a/tests/storage/test_events.py
+++ b/tests/storage/test_events.py
@@ -66,6 +66,10 @@ class ExtremPruneTestCase(HomeserverTestCase):
        body = self.helper.send(self.room_id, body="Test", tok=self.token)
        local_message_event_id = body["event_id"]

+        current_state = self.get_success(
+            self._state_storage_controller.get_current_state_ids(self.room_id)
+        )
+
        # Fudge a remote event and persist it. This will be the extremity before
        # the gap.
        self.remote_event_1 = event_from_pdu_json(
@@ -77,7 +81,11 @@ class ExtremPruneTestCase(HomeserverTestCase):
                "sender": "@user:other",
                "depth": 5,
                "prev_events": [local_message_event_id],
-                "auth_events": [],
+                "auth_events": [
+                    current_state.get((EventTypes.Create, "")),
+                    current_state.get((EventTypes.PowerLevels, "")),
+                    current_state.get((EventTypes.JoinRules, "")),
+                ],
                "origin_server_ts": self.clock.time_msec(),
            },
            RoomVersions.V6,
@@ -113,6 +121,10 @@ class ExtremPruneTestCase(HomeserverTestCase):
        the same domain.
        """

+        state_before_gap = self.get_success(
+            self._state_storage_controller.get_current_state_ids(self.room_id)
+        )
+
        # Fudge a second event which points to an event we don't have. This is a
        # state event so that the state changes (otherwise we won't prune the
        # extremity as they'll have the same state group).
@@ -125,16 +137,16 @@ class ExtremPruneTestCase(HomeserverTestCase):
                "sender": "@user:other",
                "depth": 50,
                "prev_events": ["$some_unknown_message"],
-                "auth_events": [],
+                "auth_events": [
+                    state_before_gap.get((EventTypes.Create, "")),
+                    state_before_gap.get((EventTypes.PowerLevels, "")),
+                    state_before_gap.get((EventTypes.JoinRules, "")),
+                ],
                "origin_server_ts": self.clock.time_msec(),
            },
            RoomVersions.V6,
        )

-        state_before_gap = self.get_success(
-            self._state_storage_controller.get_current_state_ids(self.room_id)
-        )
-
        self.persist_event(remote_event_2, state=state_before_gap)

        # Check the new extremity is just the new remote event.
@@ -145,6 +157,15 @@ class ExtremPruneTestCase(HomeserverTestCase):
        state is different.
        """

+        # Now we persist it with state with a dropped history visibility
+        # setting. The state resolution across the old and new event will then
+        # include it, and so the resolved state won't match the new state.
+        state_before_gap = dict(
+            self.get_success(
+                self._state_storage_controller.get_current_state_ids(self.room_id)
+            )
+        )
+
        # Fudge a second event which points to an event we don't have.
        remote_event_2 = event_from_pdu_json(
            {
@@ -155,20 +176,15 @@ class ExtremPruneTestCase(HomeserverTestCase):
                "sender": "@user:other",
                "depth": 10,
                "prev_events": ["$some_unknown_message"],
-                "auth_events": [],
+                "auth_events": [
+                    state_before_gap.get((EventTypes.Create, "")),
+                    state_before_gap.get((EventTypes.PowerLevels, "")),
+                ],
                "origin_server_ts": self.clock.time_msec(),
            },
            RoomVersions.V6,
        )

-        # Now we persist it with state with a dropped history visibility
-        # setting. The state resolution across the old and new event will then
-        # include it, and so the resolved state won't match the new state.
-        state_before_gap = dict(
-            self.get_success(
-                self._state_storage_controller.get_current_state_ids(self.room_id)
-            )
-        )
        state_before_gap.pop(("m.room.history_visibility", ""))

        context = self.get_success(
@@ -193,6 +209,10 @@ class ExtremPruneTestCase(HomeserverTestCase):
        # also set the depth to "lots".
        self.reactor.advance(7 * 24 * 60 * 60)

+        state_before_gap = self.get_success(
+            self._state_storage_controller.get_current_state_ids(self.room_id)
+        )
+
        # Fudge a second event which points to an event we don't have. This is a
        # state event so that the state changes (otherwise we won't prune the
        # extremity as they'll have the same state group).
@@ -205,16 +225,16 @@ class ExtremPruneTestCase(HomeserverTestCase):
                "sender": "@user:other2",
                "depth": 10000,
                "prev_events": ["$some_unknown_message"],
-                "auth_events": [],
+                "auth_events": [
+                    state_before_gap.get((EventTypes.Create, "")),
+                    state_before_gap.get((EventTypes.PowerLevels, "")),
+                    state_before_gap.get((EventTypes.JoinRules, "")),
+                ],
                "origin_server_ts": self.clock.time_msec(),
            },
            RoomVersions.V6,
        )

-        state_before_gap = self.get_success(
-            self._state_storage_controller.get_current_state_ids(self.room_id)
-        )
-
        self.persist_event(remote_event_2, state=state_before_gap)

        # Check the new extremity is just the new remote event.
@@ -225,6 +245,10 @@ class ExtremPruneTestCase(HomeserverTestCase):
        from a different domain.
        """

+        state_before_gap = self.get_success(
+            self._state_storage_controller.get_current_state_ids(self.room_id)
+        )
+
        # Fudge a second event which points to an event we don't have. This is a
        # state event so that the state changes (otherwise we won't prune the
        # extremity as they'll have the same state group).
@@ -237,16 +261,15 @@ class ExtremPruneTestCase(HomeserverTestCase):
                "sender": "@user:other2",
                "depth": 10,
                "prev_events": ["$some_unknown_message"],
-                "auth_events": [],
+                "auth_events": [
+                    state_before_gap.get((EventTypes.Create, "")),
+                    state_before_gap.get((EventTypes.PowerLevels, "")),
+                ],
                "origin_server_ts": self.clock.time_msec(),
            },
            RoomVersions.V6,
        )

-        state_before_gap = self.get_success(
-            self._state_storage_controller.get_current_state_ids(self.room_id)
-        )
-
        self.persist_event(remote_event_2, state=state_before_gap)

        # Check the new extremity is just the new remote event.
@@ -267,6 +290,10 @@ class ExtremPruneTestCase(HomeserverTestCase):
        # also set the depth to "lots".
        self.reactor.advance(7 * 24 * 60 * 60)

+        state_before_gap = self.get_success(
+            self._state_storage_controller.get_current_state_ids(self.room_id)
+        )
+
        # Fudge a second event which points to an event we don't have. This is a
        # state event so that the state changes (otherwise we won't prune the
        # extremity as they'll have the same state group).
@@ -279,16 +306,16 @@ class ExtremPruneTestCase(HomeserverTestCase):
                "sender": "@user:other2",
                "depth": 10000,
                "prev_events": ["$some_unknown_message"],
-                "auth_events": [],
+                "auth_events": [
+                    state_before_gap.get((EventTypes.Create, "")),
+                    state_before_gap.get((EventTypes.PowerLevels, "")),
+                    state_before_gap.get((EventTypes.JoinRules, "")),
+                ],
                "origin_server_ts": self.clock.time_msec(),
            },
            RoomVersions.V6,
        )

-        state_before_gap = self.get_success(
-            self._state_storage_controller.get_current_state_ids(self.room_id)
-        )
-
        self.persist_event(remote_event_2, state=state_before_gap)

        # Check the new extremity is just the new remote event.
@@ -311,6 +338,10 @@ class ExtremPruneTestCase(HomeserverTestCase):
        # also set the depth to "lots".
        self.reactor.advance(7 * 24 * 60 * 60)

+        state_before_gap = self.get_success(
+            self._state_storage_controller.get_current_state_ids(self.room_id)
+        )
+
        # Fudge a second event which points to an event we don't have. This is a
        # state event so that the state changes (otherwise we won't prune the
        # extremity as they'll have the same state group).
@@ -323,16 +354,16 @@ class ExtremPruneTestCase(HomeserverTestCase):
                "sender": "@user:other2",
                "depth": 10000,
                "prev_events": ["$some_unknown_message"],
-                "auth_events": [],
+                "auth_events": [
+                    state_before_gap.get((EventTypes.Create, "")),
+                    state_before_gap.get((EventTypes.PowerLevels, "")),
+                    state_before_gap.get((EventTypes.JoinRules, "")),
+                ],
                "origin_server_ts": self.clock.time_msec(),
            },
            RoomVersions.V6,
        )

-        state_before_gap = self.get_success(
-            self._state_storage_controller.get_current_state_ids(self.room_id)
-        )
-
        self.persist_event(remote_event_2, state=state_before_gap)

        # Check the new extremity is just the new remote event.
@@ -347,6 +378,10 @@ class ExtremPruneTestCase(HomeserverTestCase):
        local_message_event_id = body["event_id"]
        self.assert_extremities([local_message_event_id])

+        state_before_gap = self.get_success(
+            self._state_storage_controller.get_current_state_ids(self.room_id)
+        )
+
        # Fudge a second event which points to an event we don't have. This is a
        # state event so that the state changes (otherwise we won't prune the
        # extremity as they'll have the same state group).
@@ -359,16 +394,16 @@ class ExtremPruneTestCase(HomeserverTestCase):
                "sender": "@user:other2",
                "depth": 10000,
                "prev_events": ["$some_unknown_message"],
-                "auth_events": [],
+                "auth_events": [
+                    state_before_gap.get((EventTypes.Create, "")),
+                    state_before_gap.get((EventTypes.PowerLevels, "")),
+                    state_before_gap.get((EventTypes.JoinRules, "")),
+                ],
                "origin_server_ts": self.clock.time_msec(),
            },
            RoomVersions.V6,
        )

-        state_before_gap = self.get_success(
-            self._state_storage_controller.get_current_state_ids(self.room_id)
-        )
-
        self.persist_event(remote_event_2, state=state_before_gap)

        # Check the new extremity is just the new remote event.
--- a/tests/storage/test_redaction.py
+++ b/tests/storage/test_redaction.py
@@ -25,7 +25,7 @@ from canonicaljson import json
 from twisted.internet.testing import MemoryReactor

 from synapse.api.constants import EventTypes, Membership
-from synapse.api.room_versions import RoomVersions
+from synapse.api.room_versions import RoomVersion, RoomVersions
 from synapse.events import EventBase
 from synapse.events.builder import EventBuilder
 from synapse.server import HomeServer
@@ -263,12 +263,17 @@ class RedactionTestCase(unittest.HomeserverTestCase):

            @property
            def room_id(self) -> str:
+                assert self._base_builder.room_id is not None
                return self._base_builder.room_id

            @property
            def type(self) -> str:
                return self._base_builder.type

+            @property
+            def room_version(self) -> RoomVersion:
+                return self._base_builder.room_version
+
            @property
            def internal_metadata(self) -> EventInternalMetadata:
                return self._base_builder.internal_metadata
--- a/tests/types/test_init.py
+++ b/tests/types/test_init.py
@@ -0,0 +1,51 @@
+from synapse.api.errors import SynapseError
+from synapse.types import RoomID
+
+from tests.unittest import TestCase
+
+
+class RoomIDTestCase(TestCase):
+    def test_can_create_msc4291_room_ids(self) -> None:
+        valid_msc4291_room_id = "!31hneApxJ_1o-63DmFrpeqnkFfWppnzWso1JvH3ogLM"
+        room_id = RoomID.from_string(valid_msc4291_room_id)
+        self.assertEquals(RoomID.is_valid(valid_msc4291_room_id), True)
+        self.assertEquals(
+            room_id.to_string(),
+            valid_msc4291_room_id,
+        )
+        self.assertEquals(room_id.id, "!31hneApxJ_1o-63DmFrpeqnkFfWppnzWso1JvH3ogLM")
+        self.assertEquals(room_id.get_domain(), None)
+
+    def test_cannot_create_invalid_msc4291_room_ids(self) -> None:
+        invalid_room_ids = [
+            "!wronglength",
+            "!31hneApxJ_1o-63DmFrpeqnNOTurlsafeBASE64/gLM",
+            "!",
+            "!                                           ",
+        ]
+        for bad_room_id in invalid_room_ids:
+            with self.assertRaises(SynapseError):
+                RoomID.from_string(bad_room_id)
+                if not RoomID.is_valid(bad_room_id):
+                    raise SynapseError(400, "invalid")
+
+    def test_cannot_create_invalid_legacy_room_ids(self) -> None:
+        invalid_room_ids = [
+            "!something:invalid$_chars.com",
+        ]
+        for bad_room_id in invalid_room_ids:
+            with self.assertRaises(SynapseError):
+                RoomID.from_string(bad_room_id)
+                if not RoomID.is_valid(bad_room_id):
+                    raise SynapseError(400, "invalid")
+
+    def test_can_create_valid_legacy_room_ids(self) -> None:
+        valid_room_ids = [
+            "!foo:example.com",
+            "!foo:example.com:8448",
+            "!💩💩💩:example.com",
+        ]
+        for room_id_str in valid_room_ids:
+            room_id = RoomID.from_string(room_id_str)
+            self.assertEquals(RoomID.is_valid(room_id_str), True)
+            self.assertIsNotNone(room_id.get_domain())
Author	SHA1	Message	Date
Ben Banfield-Zanin	6ab7f0a124	Fix worker documentation around room Admin APIs	2025-08-21 14:24:40 +01:00
Andrew Morgan	40edb10a98	Linkify MSC and CVE in the changelog	2025-08-19 11:01:21 +01:00
Andrew Morgan	3d7e39b2ea	add backticks to changelog	2025-08-19 11:00:15 +01:00
Andrew Morgan	c51da9bac0	1.137.0rc1	2025-08-19 10:55:42 +01:00
Eric Eastwood	4cee8c7b99	Instrument `encode_response` with tracing in Sliding Sync requests (#18815 ) Just filling in the hole I see in the trace after `current_sync_for_user`.	2025-08-18 09:28:59 -05:00
Eric Eastwood	4ac656073d	Tag Sliding Sync traces when we `wait_for_events` (#18816 ) This way we can later filter out long-running traces where we were just waiting.	2025-08-18 09:26:36 -05:00
Quentin Gliech	3212526673	Allow enabling MSC4108 when the stable MAS integration is enabled (#18832 )	2025-08-18 11:00:51 +02:00
reivilibre	c0878ac9e6	Fix portdb CI by hardcoding the new pg_dump restrict key that was added due to CVE-2025-8714. (#18824 ) Links: - https://www.postgresql.org/support/security/CVE-2025-8714/ - `71ea0d6795` --------- Signed-off-by: Olivier 'reivilibre <oliverw@matrix.org>	2025-08-15 13:32:05 +01:00
Kegan Dougal	76c9f09e09	Fix a bug which could corrupt auth chains (#18746 ) [Complement tests](https://github.com/matrix-org/complement/pull/790) Basically, when we use `/state_ids` in conjunction with `/event` requests, the `/event` request can fail causing a partial state to be returned. When we persist the state, we process dependent events first. If we fail to process a dependent event due to missing the `auth_event`, we didn't update the in-memory event map. This meant that we could incorrectly persist events that depended on dropped events. Discovered via Chaos testing. ### Pull Request Checklist <!-- Please read https://element-hq.github.io/synapse/latest/development/contributing_guide.html before submitting your pull request --> * [x] Pull request is based on the develop branch * [x] Pull request includes a [changelog file](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#changelog). The entry should: - Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from `EventStore` to `EventWorkerStore`.". - Use markdown where necessary, mostly for `code blocks`. - End with either a period (.) or an exclamation mark (!). - Start with a capital letter. - Feel free to credit yourself, by adding a sentence "Contributed by @github_username." or "Contributed by [Your Name]." to the end of the entry. * [x] [Code style](https://element-hq.github.io/synapse/latest/code_style.html) is correct (run the [linters](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#run-the-linters))	2025-08-15 10:15:02 +01:00
Eric Eastwood	5c20a60f0b	Update tests to ensure all database tables are emptied when purging a room (#18794 ) Spawning from wanting to confirm my replies in https://github.com/element-hq/synapse/issues/18489 We're now using the same source of truth of the list of tables being purged in the tests. For example, we weren't testing that `local_current_membership` was cleared out before because the lists were out of sync.	2025-08-13 15:05:41 -05:00
dependabot[bot]	3671bdbc51	Bump slab from 0.4.10 to 0.4.11 (#18809 ) Bumps [slab](https://github.com/tokio-rs/slab) from 0.4.10 to 0.4.11. <details> <summary>Release notes</summary> <p><em>Sourced from <a href="https://github.com/tokio-rs/slab/releases">slab's releases</a>.</em></p> <blockquote> <h2>v0.4.11</h2> <ul> <li>Fix <code>Slab::get_disjoint_mut</code> out of bounds (<a href="https://redirect.github.com/tokio-rs/slab/issues/152">#152</a>)</li> </ul> </blockquote> </details> <details> <summary>Changelog</summary> <p><em>Sourced from <a href="https://github.com/tokio-rs/slab/blob/master/CHANGELOG.md">slab's changelog</a>.</em></p> <blockquote> <h1>0.4.11 (August 8, 2025)</h1> <ul> <li>Fix <code>Slab::get_disjoint_mut</code> out of bounds (<a href="https://redirect.github.com/tokio-rs/slab/issues/152">#152</a>)</li> </ul> </blockquote> </details> <details> <summary>Commits</summary> <ul> <li><a href="`2e5779f8eb`"><code>2e5779f</code></a> Release v0.4.11 (<a href="https://redirect.github.com/tokio-rs/slab/issues/153">#153</a>)</li> <li><a href="`2d65c514bc`"><code>2d65c51</code></a> Fix get_disjoint_mut error condition (<a href="https://redirect.github.com/tokio-rs/slab/issues/152">#152</a>)</li> <li>See full diff in <a href="https://github.com/tokio-rs/slab/compare/v0.4.10...v0.4.11">compare view</a></li> </ul> </details> <br /> [![Dependabot compatibility score](https://dependabot-badges.githubapp.com/badges/compatibility_score?dependency-name=slab&package-manager=cargo&previous-version=0.4.10&new-version=0.4.11)](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores) Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting `@dependabot rebase`. [//]: # (dependabot-automerge-start) [//]: # (dependabot-automerge-end) --- <details> <summary>Dependabot commands and options</summary> <br /> You can trigger Dependabot actions by commenting on this PR: - `@dependabot rebase` will rebase this PR - `@dependabot recreate` will recreate this PR, overwriting any edits that have been made to it - `@dependabot merge` will merge this PR after your CI passes on it - `@dependabot squash and merge` will squash and merge this PR after your CI passes on it - `@dependabot cancel merge` will cancel a previously requested merge and block automerging - `@dependabot reopen` will reopen this PR if it is closed - `@dependabot close` will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually - `@dependabot show <dependency name> ignore conditions` will show all of the ignore conditions of the specified dependency - `@dependabot ignore this major version` will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this minor version` will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this dependency` will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself) You can disable automated security fix PRs for this repo from the [Security Alerts page](https://github.com/element-hq/synapse/network/alerts). </details> Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>	2025-08-13 14:41:09 +00:00
dependabot[bot]	7e60ca70c8	Bump actions/add-to-project from 5b1a254a3546aef88e0a7724a77a623fa2e47c36 to 0c37450c4be3b6a7582b2fb013c9ebfd9c8e9300 (#18557 ) Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com> Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>	2025-08-13 10:32:34 +01:00
dependabot[bot]	9135d78b88	Bump docker/metadata-action from 5.7.0 to 5.8.0 (#18773 ) Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>	2025-08-12 16:45:05 +01:00
dependabot[bot]	3e10b3392f	Bump mypy from 1.16.1 to 1.17.1 (#18775 ) Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>	2025-08-12 16:43:09 +01:00
dependabot[bot]	40e4e379da	Bump serde_json from 1.0.141 to 1.0.142 (#18776 ) Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>	2025-08-12 16:39:43 +01:00
dependabot[bot]	87ba085cdf	Bump pygithub from 2.6.1 to 2.7.0 (#18779 )	2025-08-12 16:38:49 +01:00
dependabot[bot]	7e3e9a6d60	Bump types-setuptools from 80.9.0.20250529 to 80.9.0.20250809 (#18796 ) Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>	2025-08-12 16:37:15 +01:00
dependabot[bot]	874c6b38f7	Bump phonenumbers from 9.0.10 to 9.0.11 (#18797 ) Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>	2025-08-12 16:36:44 +01:00
dependabot[bot]	09aa3fc270	Bump actions/download-artifact from 4.3.0 to 5.0.0 (#18801 )	2025-08-12 16:35:55 +01:00
Andrew Morgan	14e93d8043	Merge branch 'master' of github.com:element-hq/synapse into develop	2025-08-12 15:45:26 +01:00
Andrew Morgan	6d39e3a411	Merge branch 'release-v1.136' of github.com:element-hq/synapse	2025-08-12 15:42:10 +01:00
Andrew Morgan	f7aa36926e	Revert "Merge 'release-v1.136' into 'master'" This reverts commit `283ade8e33`. This was supposed to come as a collection of commits, not squashed into one.	2025-08-12 15:38:41 +01:00
Andrew Morgan	283ade8e33	Merge 'release-v1.136' into 'master'	2025-08-12 15:37:55 +01:00
dependabot[bot]	1f155c9650	Bump types-pyyaml from 6.0.12.20250516 to 6.0.12.20250809 (#18798 ) Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>	2025-08-12 14:56:32 +01:00
dependabot[bot]	6679c719e3	Bump actions/cache from 4.2.3 to 4.2.4 (#18799 ) Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>	2025-08-12 14:55:22 +01:00
dependabot[bot]	073ce74464	Bump actions/checkout from 4.2.2 to 4.3.0 (#18800 ) Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>	2025-08-12 14:55:01 +01:00
dependabot[bot]	a93ec56cec	Bump tokio from 1.47.0 to 1.47.1 (#18774 )	2025-08-12 14:53:04 +01:00
Andrew Morgan	e8c6cb3d9e	Add security release notes	2025-08-12 13:19:58 +01:00
Andrew Morgan	3bb95d4a9d	1.136.0	2025-08-12 13:18:14 +01:00
Andrew Morgan	526b875e03	Make the Make Room Admin API choose to puppet the room creator in v12 rooms (#18805 )	2025-08-12 10:11:03 +00:00
Devon Hudson	d27438bc25	Merge branch 'release-v1.135' into develop	2025-08-11 13:05:37 -06:00
Devon Hudson	8f375ea6c1	Merge branch 'release-v1.136' into develop	2025-08-11 12:56:12 -06:00
Devon Hudson	3db9fa3eeb	1.136.0rc2	2025-08-11 12:19:31 -06:00
V02460	0c0a9fafde	register_new_matrix_user: Fix error message for registration shared secret (#18780 ) Fixes the error message in `register_new_matrix_user` for an empty registration shared secret read from file.	2025-08-11 13:18:34 -05:00
Devon Hudson	4054d956f7	Fix changelog versions	2025-08-11 11:53:30 -06:00
Devon Hudson	04932c76f5	1.135.2	2025-08-11 11:52:37 -06:00
Devon Hudson	9244948750	Merge remote-tracking branch 'private/release-v1.135-hydra' into release-v1.135	2025-08-11 11:50:12 -06:00
Devon Hudson	fdd63882b1	Fix hydra tests	2025-08-11 11:35:32 -06:00
Devon Hudson	1e45f35eb6	Add missing additional_creators field	2025-08-11 11:35:24 -06:00
Devon Hudson	9301baa5f8	Fix hydra tests	2025-08-11 11:32:57 -06:00
Devon Hudson	576022912b	Add missing additional_creators field	2025-08-11 11:32:31 -06:00
Devon Hudson	848949a727	1.135.1	2025-08-11 11:14:00 -06:00
Andrew Morgan	3f37bd6277	Update impl of `_calculate_upgraded_room_creation_content`	2025-08-11 16:46:12 +01:00
Andrew Morgan	a89afc733b	Add `HydraV11` to known room versions	2025-08-11 16:46:09 +01:00
Andrew Morgan	f0656a3b06	Update impl of `_calculate_upgraded_room_creation_content`	2025-08-11 16:45:40 +01:00
Andrew Morgan	2c434e5187	Add `HydraV11` to known room versions	2025-08-11 16:44:30 +01:00
Devon Hudson	9f579b36c8	Update MSC4293 redact logic for hydra (#80 )	2025-08-11 16:43:45 +01:00
Erik Johnston	a407357eec	Add a parameter to allow room upgrades to auto join local users (#83 )	2025-08-11 16:43:45 +01:00
Devon Hudson	92b0077b27	Update changelog	2025-08-11 16:43:45 +01:00
Andrew Morgan	7e8782f47f	Set type of `user_id` on `is_server_admin` to str (#18786 )	2025-08-11 16:43:45 +01:00
Devon Hudson	8fe3c73f95	Update changelog	2025-08-11 16:43:45 +01:00
Devon Hudson	81f815ee33	Remove unnecessary extra deferred	2025-08-11 16:43:45 +01:00
Devon Hudson	3108fa32d3	Use internal function to appease olddeps test	2025-08-11 16:43:45 +01:00
Devon Hudson	a1a40523ae	Fix olddeps & mypy errors	2025-08-11 16:43:45 +01:00
Devon Hudson	e65a6fc58a	Fix FakeClock to match new sleep signature	2025-08-11 16:43:45 +01:00
Devon Hudson	bd8f12f9c6	Fix broken test	2025-08-11 16:43:45 +01:00
Kegan Dougal	0eb7252a23	Support for room version 12	2025-08-11 16:43:45 +01:00
Erik Johnston	15146c2259	Newsfile	2025-08-11 16:14:48 +01:00
Erik Johnston	340e4de5af	Add a parameter to allow room upgrades to auto join local users	2025-08-11 16:14:32 +01:00
Erik Johnston	88a24bdd13	Make room upgrades faster for rooms with many bans (#18574 ) We do this by a) not pulling out all membership events, and b) batch inserting bans. One blocking concern is that this bypasses the `update_membership` function, which otherwise all other membership events go via. In this case it's fine (having audited what it is doing), but I'm hesitant to set the precedent of bypassing it, given it has a lot of logic in there. --------- Co-authored-by: Eric Eastwood <erice@element.io>	2025-08-11 16:13:46 +01:00
Andrew Morgan	7aac7db652	Set type of `user_id` on `is_server_admin` to str (#18786 )	2025-08-11 16:13:41 +01:00
Devon Hudson	a8886d3351	Use internal function to appease olddeps test	2025-08-11 16:13:24 +01:00
Devon Hudson	da23e8acde	Make attr autogenerate init	2025-08-11 16:13:24 +01:00
Devon Hudson	2f3a075514	Fix olddeps test	2025-08-11 16:13:24 +01:00
Devon Hudson	87d80b0f9a	Fix broken test	2025-08-11 16:13:24 +01:00
Kegan Dougal	731e81c9a3	Support for room version 12	2025-08-11 16:13:24 +01:00
litetex	6dd6bb4714	Include IPv6 networks in denied-peer-ips of coturn setup docs (#18781 ) Fixes #18771	2025-08-07 12:50:56 -05:00
				`@@ -0,0 +1 @@`
				`Fix worker documentation incorrectly indicating all room Admin API requests were capable of being handled by workers.`