Merge remote-tracking branch 'origin/develop' into matrix-org-hotfixes

58 files changed, 731 insertions, 306 deletions

diff --git a/.ci/scripts/calculate_jobs.py b/.ci/scripts/calculate_jobs.py
index b1f604eeb0..c2198e0dd4 100755
--- a/.ci/scripts/calculate_jobs.py
+++ b/.ci/scripts/calculate_jobs.py
@@ -18,6 +18,13 @@
 import json
 import os
 
+
+def set_output(key: str, value: str):
+    # See https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter
+    with open(os.environ["GITHUB_OUTPUT"], "at") as f:
+        print(f"{key}={value}", file=f)
+
+
 IS_PR = os.environ["GITHUB_REF"].startswith("refs/pull/")
 
 # First calculate the various trial jobs.
@@ -81,7 +88,7 @@ print("::endgroup::")
 test_matrix = json.dumps(
     trial_sqlite_tests + trial_postgres_tests + trial_no_extra_tests
 )
-print(f"::set-output name=trial_test_matrix::{test_matrix}")
+set_output("trial_test_matrix", test_matrix)
 
 
 # First calculate the various sytest jobs.
@@ -125,4 +132,4 @@ print(json.dumps(sytest_tests, indent=4))
 print("::endgroup::")
 
 test_matrix = json.dumps(sytest_tests)
-print(f"::set-output name=sytest_test_matrix::{test_matrix}")
+set_output("sytest_test_matrix", test_matrix)
diff --git a/.github/workflows/docs.yaml b/.github/workflows/docs.yaml
index 17b9df601c..798e308f20 100644
--- a/.github/workflows/docs.yaml
+++ b/.github/workflows/docs.yaml
@@ -54,7 +54,7 @@ jobs:
           esac
 
           # finally, set the 'branch-version' var.
-          echo "::set-output name=branch-version::$branch"
+          echo "branch-version=$branch" >> "$GITHUB_OUTPUT"
           
       # Deploy to the target directory.
       - name: Deploy to gh pages
diff --git a/.github/workflows/release-artifacts.yml b/.github/workflows/release-artifacts.yml
index 1c004fbc11..60db6ad7f0 100644
--- a/.github/workflows/release-artifacts.yml
+++ b/.github/workflows/release-artifacts.yml
@@ -27,6 +27,8 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4
+        with:
+          python-version: '3.x'
       - id: set-distros
         run: |
           # if we're running from a tag, get the full list of distros; otherwise just use debian:sid
@@ -34,7 +36,7 @@ jobs:
           if [[ $GITHUB_REF == refs/tags/* ]]; then
               dists=$(scripts-dev/build_debian_packages.py --show-dists-json)
           fi
-          echo "::set-output name=distros::$dists"
+          echo "distros=$dists" >> "$GITHUB_OUTPUT"
     # map the step outputs to job outputs
     outputs:
       distros: ${{ steps.set-distros.outputs.distros }}
@@ -70,6 +72,8 @@ jobs:
 
       - name: Set up python
         uses: actions/setup-python@v4
+        with:
+          python-version: '3.x'
 
       - name: Build the packages
         # see https://github.com/docker/build-push-action/issues/252
@@ -91,11 +95,14 @@ jobs:
           path: debs/*
 
   build-wheels:
-    name: Build wheels on ${{ matrix.os }}
+    name: Build wheels on ${{ matrix.os }} for ${{ matrix.arch }}
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
         os: [ubuntu-20.04, macos-10.15]
+        arch: [x86_64, aarch64]
+        # is_pr is a flag used to exclude certain jobs from the matrix on PRs.
+        # It is not read by the rest of the workflow.
         is_pr:
           - ${{ startsWith(github.ref, 'refs/pull/') }}
 
@@ -103,6 +110,12 @@ jobs:
           # Don't build macos wheels on PR CI.
           - is_pr: true
             os: "macos-10.15"
+          # Don't build aarch64 wheels on mac.
+          - os: "macos-10.15"
+            arch: aarch64
+          # Don't build aarch64 wheels on PR CI.
+          - is_pr: true
+            arch: aarch64
 
     steps:
       - uses: actions/checkout@v3
@@ -116,11 +129,19 @@ jobs:
       - name: Install cibuildwheel
         run: python -m pip install cibuildwheel==2.9.0 poetry==1.2.0
 
-      # Only build a single wheel in CI.
-      - name: Set env vars.
-        run: |
-          echo "CIBW_BUILD="cp37-manylinux_x86_64"" >> $GITHUB_ENV
+      - name: Set up QEMU to emulate aarch64
+        if: matrix.arch == 'aarch64'
+        uses: docker/setup-qemu-action@v2
+        with:
+          platforms: arm64
+
+      - name: Build aarch64 wheels
+        if: matrix.arch == 'aarch64'
+        run: echo 'CIBW_ARCHS_LINUX=aarch64' >> $GITHUB_ENV
+
+      - name: Only build a single wheel on PR
         if: startsWith(github.ref, 'refs/pull/')
+        run: echo "CIBW_BUILD="cp37-manylinux_${{ matrix.arch }}"" >> $GITHUB_ENV
 
       - name: Build wheels
         run: python -m cibuildwheel --output-dir wheelhouse
@@ -128,6 +149,9 @@ jobs:
           # Skip testing for platforms which various libraries don't have wheels
           # for, and so need extra build deps.
           CIBW_TEST_SKIP: pp39-* *i686* *musl* pp37-macosx*
+          # Fix Rust OOM errors on emulated aarch64: https://github.com/rust-lang/cargo/issues/10583
+          CARGO_NET_GIT_FETCH_WITH_CLI: true
+          CIBW_ENVIRONMENT_PASS_LINUX: CARGO_NET_GIT_FETCH_WITH_CLI
 
       - uses: actions/upload-artifact@v3
         with:
diff --git a/changelog.d/10015.bugfix b/changelog.d/10015.bugfix
new file mode 100644
index 0000000000..cbebd97e58
--- /dev/null
+++ b/changelog.d/10015.bugfix
@@ -0,0 +1 @@
+Prevent device names from appearing in device list updates when `allow_device_name_lookup_over_federation` is `false`.
\ No newline at end of file
diff --git a/changelog.d/14018.feature b/changelog.d/14018.feature
new file mode 100644
index 0000000000..c8454607eb
--- /dev/null
+++ b/changelog.d/14018.feature
@@ -0,0 +1 @@
+Support for redirecting to an implementation of a [MSC3886](https://github.com/matrix-org/matrix-spec-proposals/pull/3886) HTTP rendezvous service.
\ No newline at end of file
diff --git a/changelog.d/14126.misc b/changelog.d/14126.misc
new file mode 100644
index 0000000000..30b3482fbd
--- /dev/null
+++ b/changelog.d/14126.misc
@@ -0,0 +1 @@
+Faster joins: prioritise the server we joined by when restarting a partial join resync.
diff --git a/changelog.d/14145.doc b/changelog.d/14145.doc
new file mode 100644
index 0000000000..8f876e08fc
--- /dev/null
+++ b/changelog.d/14145.doc
@@ -0,0 +1,2 @@
+Clarify comment on event contexts.
+
diff --git a/changelog.d/14195.docker b/changelog.d/14195.docker
new file mode 100644
index 0000000000..d755a79599
--- /dev/null
+++ b/changelog.d/14195.docker
@@ -0,0 +1 @@
+Fix pre-startup logging being lost when using the `Dockerfile-workers` image.
diff --git a/changelog.d/14198.misc b/changelog.d/14198.misc
new file mode 100644
index 0000000000..9d56f8a2c6
--- /dev/null
+++ b/changelog.d/14198.misc
@@ -0,0 +1 @@
+Enable url previews when testing with complement.
\ No newline at end of file
diff --git a/changelog.d/14206.misc b/changelog.d/14206.misc
new file mode 100644
index 0000000000..005e1225a4
--- /dev/null
+++ b/changelog.d/14206.misc
@@ -0,0 +1 @@
+Bump pygithub from 1.55 to 1.56.
diff --git a/changelog.d/14207.misc b/changelog.d/14207.misc
new file mode 100644
index 0000000000..1f2d99e9b0
--- /dev/null
+++ b/changelog.d/14207.misc
@@ -0,0 +1 @@
+Bump twisted from 22.4.0 to 22.8.0.
diff --git a/changelog.d/14208.misc b/changelog.d/14208.misc
new file mode 100644
index 0000000000..6d4c196228
--- /dev/null
+++ b/changelog.d/14208.misc
@@ -0,0 +1 @@
+Bump types-setuptools from 65.4.0.0 to 65.5.0.1.
diff --git a/changelog.d/14212.feature b/changelog.d/14212.feature
new file mode 100644
index 0000000000..53b135cb5c
--- /dev/null
+++ b/changelog.d/14212.feature
@@ -0,0 +1 @@
+Build and publish binary wheels for `aarch64` platforms.
\ No newline at end of file
diff --git a/changelog.d/14214.misc b/changelog.d/14214.misc
new file mode 100644
index 0000000000..102928b575
--- /dev/null
+++ b/changelog.d/14214.misc
@@ -0,0 +1 @@
+When authenticating batched events, check for auth events in batch as well as DB.
diff --git a/changelog.d/14215.bugfix b/changelog.d/14215.bugfix
new file mode 100644
index 0000000000..31c109f534
--- /dev/null
+++ b/changelog.d/14215.bugfix
@@ -0,0 +1 @@
+Fix [MSC3030](https://github.com/matrix-org/matrix-spec-proposals/pull/3030) `/timestamp_to_event` endpoint returning potentially inaccurate closest events with `outliers` present.
diff --git a/changelog.d/14216.misc b/changelog.d/14216.misc
new file mode 100644
index 0000000000..6fad16d83d
--- /dev/null
+++ b/changelog.d/14216.misc
@@ -0,0 +1 @@
+Update CI config to avoid GitHub Actions deprecation warnings.
diff --git a/changelog.d/14221.misc b/changelog.d/14221.misc
new file mode 100644
index 0000000000..fe7afac245
--- /dev/null
+++ b/changelog.d/14221.misc
@@ -0,0 +1 @@
+Rename the `cache_memory` extra to `cache-memory`, for compatability with poetry-core 1.3.0 and [PEP 685](https://peps.python.org/pep-0685/). From-source installations using this extra will need to install using the new name.
diff --git a/changelog.d/14222.feature b/changelog.d/14222.feature
new file mode 100644
index 0000000000..5d0ae16e13
--- /dev/null
+++ b/changelog.d/14222.feature
@@ -0,0 +1 @@
+Support for thread-specific notifications & receipts ([MSC3771](https://github.com/matrix-org/matrix-spec-proposals/pull/3771) and [MSC3773](https://github.com/matrix-org/matrix-spec-proposals/pull/3773)).
diff --git a/changelog.d/14224.misc b/changelog.d/14224.misc
new file mode 100644
index 0000000000..6fad16d83d
--- /dev/null
+++ b/changelog.d/14224.misc
@@ -0,0 +1 @@
+Update CI config to avoid GitHub Actions deprecation warnings.
diff --git a/changelog.d/14227.misc b/changelog.d/14227.misc
new file mode 100644
index 0000000000..103c71b390
--- /dev/null
+++ b/changelog.d/14227.misc
@@ -0,0 +1 @@
+Specify dev-dependencies using lower bounds, to reduce the likelihood of a dependabot merge conflict. The lockfile continues to pin to specific versions.
diff --git a/docker/complement/conf/workers-shared-extra.yaml.j2 b/docker/complement/conf/workers-shared-extra.yaml.j2
index 9e554a865e..c651645115 100644
--- a/docker/complement/conf/workers-shared-extra.yaml.j2
+++ b/docker/complement/conf/workers-shared-extra.yaml.j2
@@ -12,6 +12,8 @@ trusted_key_servers: []
 enable_registration: true
 enable_registration_without_verification: true
 bcrypt_rounds: 4
+url_preview_enabled: true
+url_preview_ip_range_blacklist: []
 
 ## Registration ##
 
diff --git a/docker/configure_workers_and_start.py b/docker/configure_workers_and_start.py
index 60a5c10ea7..1ea456b2f8 100755
--- a/docker/configure_workers_and_start.py
+++ b/docker/configure_workers_and_start.py
@@ -230,24 +230,19 @@ upstream {upstream_worker_type} {{
 
 # Utility functions
 def log(txt: str) -> None:
-    """Log something to the stdout.
-
-    Args:
-        txt: The text to log.
-    """
     print(txt)
 
 
 def error(txt: str) -> NoReturn:
-    """Log something and exit with an error code.
-
-    Args:
-        txt: The text to log in error.
-    """
-    log(txt)
+    print(txt, file=sys.stderr)
     sys.exit(2)
 
 
+def flush_buffers() -> None:
+    sys.stdout.flush()
+    sys.stderr.flush()
+
+
 def convert(src: str, dst: str, **template_vars: object) -> None:
     """Generate a file from a template
 
@@ -328,7 +323,7 @@ def generate_base_homeserver_config() -> None:
     # start.py already does this for us, so just call that.
     # note that this script is copied in in the official, monolith dockerfile
     os.environ["SYNAPSE_HTTP_PORT"] = str(MAIN_PROCESS_HTTP_LISTENER_PORT)
-    subprocess.check_output(["/usr/local/bin/python", "/start.py", "migrate_config"])
+    subprocess.run(["/usr/local/bin/python", "/start.py", "migrate_config"], check=True)
 
 
 def generate_worker_files(
@@ -642,6 +637,7 @@ def main(args: List[str], environ: MutableMapping[str, str]) -> None:
     # Start supervisord, which will start Synapse, all of the configured worker
     # processes, redis, nginx etc. according to the config we created above.
     log("Starting supervisord")
+    flush_buffers()
     os.execle(
         "/usr/local/bin/supervisord",
         "supervisord",
diff --git a/docker/start.py b/docker/start.py
index 5a98dce551..ebcc599f04 100755
--- a/docker/start.py
+++ b/docker/start.py
@@ -13,14 +13,19 @@ import jinja2
 
 # Utility functions
 def log(txt: str) -> None:
-    print(txt, file=sys.stderr)
+    print(txt)
 
 
 def error(txt: str) -> NoReturn:
-    log(txt)
+    print(txt, file=sys.stderr)
     sys.exit(2)
 
 
+def flush_buffers() -> None:
+    sys.stdout.flush()
+    sys.stderr.flush()
+
+
 def convert(src: str, dst: str, environ: Mapping[str, object]) -> None:
     """Generate a file from a template
 
@@ -131,10 +136,10 @@ def generate_config_from_template(
 
     if ownership is not None:
         log(f"Setting ownership on /data to {ownership}")
-        subprocess.check_output(["chown", "-R", ownership, "/data"])
+        subprocess.run(["chown", "-R", ownership, "/data"], check=True)
         args = ["gosu", ownership] + args
 
-    subprocess.check_output(args)
+    subprocess.run(args, check=True)
 
 
 def run_generate_config(environ: Mapping[str, str], ownership: Optional[str]) -> None:
@@ -158,7 +163,7 @@ def run_generate_config(environ: Mapping[str, str], ownership: Optional[str]) ->
     if ownership is not None:
         # make sure that synapse has perms to write to the data dir.
         log(f"Setting ownership on {data_dir} to {ownership}")
-        subprocess.check_output(["chown", ownership, data_dir])
+        subprocess.run(["chown", ownership, data_dir], check=True)
 
     # create a suitable log config from our template
     log_config_file = "%s/%s.log.config" % (config_dir, server_name)
@@ -185,6 +190,7 @@ def run_generate_config(environ: Mapping[str, str], ownership: Optional[str]) ->
         "--open-private-ports",
     ]
     # log("running %s" % (args, ))
+    flush_buffers()
     os.execv(sys.executable, args)
 
 
@@ -267,8 +273,10 @@ running with 'migrate_config'. See the README for more details.
     args = [sys.executable] + args
     if ownership is not None:
         args = ["gosu", ownership] + args
+        flush_buffers()
         os.execve("/usr/sbin/gosu", args, environ)
     else:
+        flush_buffers()
         os.execve(sys.executable, args, environ)
 
 
diff --git a/poetry.lock b/poetry.lock
index f76b010fd0..ed0b59fbe5 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -810,7 +810,7 @@ python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 
 [[package]]
 name = "pygithub"
-version = "1.55"
+version = "1.56"
 description = "Use the full Github API v3"
 category = "dev"
 optional = false
@@ -1308,11 +1308,11 @@ urllib3 = ">=1.26.0"
 
 [[package]]
 name = "twisted"
-version = "22.4.0"
+version = "22.8.0"
 description = "An asynchronous networking framework written in Python"
 category = "main"
 optional = false
-python-versions = ">=3.6.7"
+python-versions = ">=3.7.1"
 
 [package.dependencies]
 attrs = ">=19.2.0"
@@ -1321,27 +1321,28 @@ constantly = ">=15.1"
 hyperlink = ">=17.1.1"
 idna = {version = ">=2.4", optional = true, markers = "extra == \"tls\""}
 incremental = ">=21.3.0"
-pyopenssl = {version = ">=16.0.0", optional = true, markers = "extra == \"tls\""}
+pyopenssl = {version = ">=21.0.0", optional = true, markers = "extra == \"tls\""}
 service-identity = {version = ">=18.1.0", optional = true, markers = "extra == \"tls\""}
 twisted-iocpsupport = {version = ">=1.0.2,<2", markers = "platform_system == \"Windows\""}
 typing-extensions = ">=3.6.5"
 "zope.interface" = ">=4.4.2"
 
 [package.extras]
-all-non-platform = ["PyHamcrest (>=1.9.0)", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "contextvars (>=2.4,<3)", "cryptography (>=2.6)", "cython-test-exception-raiser (>=1.0.2,<2)", "h2 (>=3.0,<5.0)", "idna (>=2.4)", "priority (>=1.1.0,<2.0)", "pyasn1", "pyopenssl (>=16.0.0)", "pyserial (>=3.0)", "pywin32 (!=226)", "service-identity (>=18.1.0)"]
+all-non-platform = ["PyHamcrest (>=1.9.0)", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "contextvars (>=2.4,<3)", "cryptography (>=2.6)", "cython-test-exception-raiser (>=1.0.2,<2)", "h2 (>=3.0,<5.0)", "idna (>=2.4)", "priority (>=1.1.0,<2.0)", "pyasn1", "pyopenssl (>=21.0.0)", "pyserial (>=3.0)", "pywin32 (!=226)", "service-identity (>=18.1.0)"]
 conch = ["appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "cryptography (>=2.6)", "pyasn1"]
 conch-nacl = ["PyNaCl", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "cryptography (>=2.6)", "pyasn1"]
 contextvars = ["contextvars (>=2.4,<3)"]
-dev = ["coverage (>=6b1,<7)", "pydoctor (>=21.9.0,<21.10.0)", "pyflakes (>=2.2,<3.0)", "python-subunit (>=1.4,<2.0)", "readthedocs-sphinx-ext (>=2.1,<3.0)", "sphinx (>=4.1.2,<6)", "sphinx-rtd-theme (>=0.5,<1.0)", "towncrier (>=19.2,<20.0)", "twistedchecker (>=0.7,<1.0)"]
-dev-release = ["pydoctor (>=21.9.0,<21.10.0)", "readthedocs-sphinx-ext (>=2.1,<3.0)", "sphinx (>=4.1.2,<6)", "sphinx-rtd-theme (>=0.5,<1.0)", "towncrier (>=19.2,<20.0)"]
+dev = ["coverage (>=6b1,<7)", "pydoctor (>=22.7.0,<22.8.0)", "pyflakes (>=2.2,<3.0)", "python-subunit (>=1.4,<2.0)", "readthedocs-sphinx-ext (>=2.1,<3.0)", "sphinx (>=4.1.2,<6)", "sphinx-rtd-theme (>=0.5,<1.0)", "towncrier (>=19.2,<20.0)", "twistedchecker (>=0.7,<1.0)"]
+dev-release = ["pydoctor (>=22.7.0,<22.8.0)", "readthedocs-sphinx-ext (>=2.1,<3.0)", "sphinx (>=4.1.2,<6)", "sphinx-rtd-theme (>=0.5,<1.0)", "towncrier (>=19.2,<20.0)"]
+gtk-platform = ["PyHamcrest (>=1.9.0)", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "contextvars (>=2.4,<3)", "cryptography (>=2.6)", "cython-test-exception-raiser (>=1.0.2,<2)", "h2 (>=3.0,<5.0)", "idna (>=2.4)", "priority (>=1.1.0,<2.0)", "pyasn1", "pygobject", "pyopenssl (>=21.0.0)", "pyserial (>=3.0)", "pywin32 (!=226)", "service-identity (>=18.1.0)"]
 http2 = ["h2 (>=3.0,<5.0)", "priority (>=1.1.0,<2.0)"]
-macos-platform = ["PyHamcrest (>=1.9.0)", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "contextvars (>=2.4,<3)", "cryptography (>=2.6)", "cython-test-exception-raiser (>=1.0.2,<2)", "h2 (>=3.0,<5.0)", "idna (>=2.4)", "priority (>=1.1.0,<2.0)", "pyasn1", "pyobjc-core", "pyobjc-framework-CFNetwork", "pyobjc-framework-Cocoa", "pyopenssl (>=16.0.0)", "pyserial (>=3.0)", "pywin32 (!=226)", "service-identity (>=18.1.0)"]
-mypy = ["PyHamcrest (>=1.9.0)", "PyNaCl", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "contextvars (>=2.4,<3)", "coverage (>=6b1,<7)", "cryptography (>=2.6)", "cython-test-exception-raiser (>=1.0.2,<2)", "h2 (>=3.0,<5.0)", "idna (>=2.4)", "mypy (==0.930)", "mypy-zope (==0.3.4)", "priority (>=1.1.0,<2.0)", "pyasn1", "pydoctor (>=21.9.0,<21.10.0)", "pyflakes (>=2.2,<3.0)", "pyopenssl (>=16.0.0)", "pyserial (>=3.0)", "python-subunit (>=1.4,<2.0)", "pywin32 (!=226)", "readthedocs-sphinx-ext (>=2.1,<3.0)", "service-identity (>=18.1.0)", "sphinx (>=4.1.2,<6)", "sphinx-rtd-theme (>=0.5,<1.0)", "towncrier (>=19.2,<20.0)", "twistedchecker (>=0.7,<1.0)", "types-pyOpenSSL", "types-setuptools"]
-osx-platform = ["PyHamcrest (>=1.9.0)", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "contextvars (>=2.4,<3)", "cryptography (>=2.6)", "cython-test-exception-raiser (>=1.0.2,<2)", "h2 (>=3.0,<5.0)", "idna (>=2.4)", "priority (>=1.1.0,<2.0)", "pyasn1", "pyobjc-core", "pyobjc-framework-CFNetwork", "pyobjc-framework-Cocoa", "pyopenssl (>=16.0.0)", "pyserial (>=3.0)", "pywin32 (!=226)", "service-identity (>=18.1.0)"]
+macos-platform = ["PyHamcrest (>=1.9.0)", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "contextvars (>=2.4,<3)", "cryptography (>=2.6)", "cython-test-exception-raiser (>=1.0.2,<2)", "h2 (>=3.0,<5.0)", "idna (>=2.4)", "priority (>=1.1.0,<2.0)", "pyasn1", "pyobjc-core", "pyobjc-framework-CFNetwork", "pyobjc-framework-Cocoa", "pyopenssl (>=21.0.0)", "pyserial (>=3.0)", "pywin32 (!=226)", "service-identity (>=18.1.0)"]
+mypy = ["PyHamcrest (>=1.9.0)", "PyNaCl", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "contextvars (>=2.4,<3)", "coverage (>=6b1,<7)", "cryptography (>=2.6)", "cython-test-exception-raiser (>=1.0.2,<2)", "h2 (>=3.0,<5.0)", "idna (>=2.4)", "mypy (==0.930)", "mypy-zope (==0.3.4)", "priority (>=1.1.0,<2.0)", "pyasn1", "pydoctor (>=22.7.0,<22.8.0)", "pyflakes (>=2.2,<3.0)", "pyopenssl (>=21.0.0)", "pyserial (>=3.0)", "python-subunit (>=1.4,<2.0)", "pywin32 (!=226)", "readthedocs-sphinx-ext (>=2.1,<3.0)", "service-identity (>=18.1.0)", "sphinx (>=4.1.2,<6)", "sphinx-rtd-theme (>=0.5,<1.0)", "towncrier (>=19.2,<20.0)", "twistedchecker (>=0.7,<1.0)", "types-pyOpenSSL", "types-setuptools"]
+osx-platform = ["PyHamcrest (>=1.9.0)", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "contextvars (>=2.4,<3)", "cryptography (>=2.6)", "cython-test-exception-raiser (>=1.0.2,<2)", "h2 (>=3.0,<5.0)", "idna (>=2.4)", "priority (>=1.1.0,<2.0)", "pyasn1", "pyobjc-core", "pyobjc-framework-CFNetwork", "pyobjc-framework-Cocoa", "pyopenssl (>=21.0.0)", "pyserial (>=3.0)", "pywin32 (!=226)", "service-identity (>=18.1.0)"]
 serial = ["pyserial (>=3.0)", "pywin32 (!=226)"]
 test = ["PyHamcrest (>=1.9.0)", "cython-test-exception-raiser (>=1.0.2,<2)"]
-tls = ["idna (>=2.4)", "pyopenssl (>=16.0.0)", "service-identity (>=18.1.0)"]
-windows-platform = ["PyHamcrest (>=1.9.0)", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "contextvars (>=2.4,<3)", "cryptography (>=2.6)", "cython-test-exception-raiser (>=1.0.2,<2)", "h2 (>=3.0,<5.0)", "idna (>=2.4)", "priority (>=1.1.0,<2.0)", "pyasn1", "pyopenssl (>=16.0.0)", "pyserial (>=3.0)", "pywin32 (!=226)", "pywin32 (!=226)", "service-identity (>=18.1.0)"]
+tls = ["idna (>=2.4)", "pyopenssl (>=21.0.0)", "service-identity (>=18.1.0)"]
+windows-platform = ["PyHamcrest (>=1.9.0)", "appdirs (>=1.4.0)", "bcrypt (>=3.0.0)", "contextvars (>=2.4,<3)", "cryptography (>=2.6)", "cython-test-exception-raiser (>=1.0.2,<2)", "h2 (>=3.0,<5.0)", "idna (>=2.4)", "priority (>=1.1.0,<2.0)", "pyasn1", "pyopenssl (>=21.0.0)", "pyserial (>=3.0)", "pywin32 (!=226)", "pywin32 (!=226)", "service-identity (>=18.1.0)"]
 
 [[package]]
 name = "twisted-iocpsupport"
@@ -1479,7 +1480,7 @@ types-urllib3 = "<1.27"
 
 [[package]]
 name = "types-setuptools"
-version = "65.4.0.0"
+version = "65.5.0.1"
 description = "Typing stubs for setuptools"
 category = "dev"
 optional = false
@@ -1632,7 +1633,7 @@ url-preview = ["lxml"]
 [metadata]
 lock-version = "1.1"
 python-versions = "^3.7.1"
-content-hash = "327eb55e543f29feac9ca1a014f17c48fdf01a96bbed9ed9237dab787e9ac614"
+content-hash = "9400cb5c92bb4648238f652f5e7f81df51cdcf9b7c69d645f35beaa4acb2f420"
 
 [metadata.files]
 attrs = [
@@ -2381,8 +2382,8 @@ pyflakes = [
     {file = "pyflakes-2.4.0.tar.gz", hash = "sha256:05a85c2872edf37a4ed30b0cce2f6093e1d0581f8c19d7393122da7e25b2b24c"},
 ]
 pygithub = [
-    {file = "PyGithub-1.55-py3-none-any.whl", hash = "sha256:2caf0054ea079b71e539741ae56c5a95e073b81fa472ce222e81667381b9601b"},
-    {file = "PyGithub-1.55.tar.gz", hash = "sha256:1bbfff9372047ff3f21d5cd8e07720f3dbfdaf6462fcaed9d815f528f1ba7283"},
+    {file = "PyGithub-1.56-py3-none-any.whl", hash = "sha256:d15f13d82165306da8a68aefc0f848a6f6432d5febbff13b60a94758ce3ef8b5"},
+    {file = "PyGithub-1.56.tar.gz", hash = "sha256:80c6d85cf0f9418ffeb840fd105840af694c4f17e102970badbaf678251f2a01"},
 ]
 pygments = [
     {file = "Pygments-2.11.2-py3-none-any.whl", hash = "sha256:44238f1b60a76d78fc8ca0528ee429702aae011c265fe6a8dd8b63049ae41c65"},
@@ -2694,8 +2695,8 @@ twine = [
     {file = "twine-3.8.0.tar.gz", hash = "sha256:8efa52658e0ae770686a13b675569328f1fba9837e5de1867bfe5f46a9aefe19"},
 ]
 twisted = [
-    {file = "Twisted-22.4.0-py3-none-any.whl", hash = "sha256:f9f7a91f94932477a9fc3b169d57f54f96c6e74a23d78d9ce54039a7f48928a2"},
-    {file = "Twisted-22.4.0.tar.gz", hash = "sha256:a047990f57dfae1e0bd2b7df2526d4f16dcdc843774dc108b78c52f2a5f13680"},
+    {file = "Twisted-22.8.0-py3-none-any.whl", hash = "sha256:8d4718d1e48dcc28933f8beb48dc71cfe77a125e37ad1eb7a3d0acc49baf6c99"},
+    {file = "Twisted-22.8.0.tar.gz", hash = "sha256:e5b60de39f2d1da153fbe1874d885fe3fcbdb21fcc446fa759a53e8fc3513bed"},
 ]
 twisted-iocpsupport = [
     {file = "twisted-iocpsupport-1.0.2.tar.gz", hash = "sha256:72068b206ee809c9c596b57b5287259ea41ddb4774d86725b19f35bf56aa32a9"},
@@ -2790,8 +2791,8 @@ types-requests = [
     {file = "types_requests-2.28.11-py3-none-any.whl", hash = "sha256:af5f55e803cabcfb836dad752bd6d8a0fc8ef1cd84243061c0e27dee04ccf4fd"},
 ]
 types-setuptools = [
-    {file = "types-setuptools-65.4.0.0.tar.gz", hash = "sha256:d9021d6a70690b34e7bd2947e7ab10167c646fbf062508cb56581be2e2a1615e"},
-    {file = "types_setuptools-65.4.0.0-py3-none-any.whl", hash = "sha256:ce178b3f7dbd6c0e67f8eee7ae29c1be280ade7e5188bdd9e620843de4060d85"},
+    {file = "types-setuptools-65.5.0.1.tar.gz", hash = "sha256:5b297081c8f1fbd992cd8b305a97ed96ee6ffc765e9115124029597dd10b8a71"},
+    {file = "types_setuptools-65.5.0.1-py3-none-any.whl", hash = "sha256:601d45b5e9979d2b931de5403aa11153626a1eadd1ce9727b21f24673ced5ceb"},
 ]
 types-urllib3 = [
     {file = "types-urllib3-1.26.10.tar.gz", hash = "sha256:a26898f530e6c3f43f25b907f2b884486868ffd56a9faa94cbf9b3eb6e165d6a"},
diff --git a/pyproject.toml b/pyproject.toml
index 7fbbc08915..554eed0fa4 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -227,7 +227,7 @@ jwt = ["authlib"]
 # (if it is not installed, we fall back to slow code.)
 redis = ["txredisapi", "hiredis"]
 # Required to use experimental `caches.track_memory_usage` config option.
-cache_memory = ["pympler"]
+cache-memory = ["pympler"]
 test = ["parameterized", "idna"]
 
 # The duplication here is awful. I hate hate hate hate hate it. However, for now I want
@@ -258,7 +258,7 @@ all = [
     "jaeger-client", "opentracing",
     # redis
     "txredisapi", "hiredis",
-    # cache_memory
+    # cache-memory
     "pympler",
     # omitted:
     #   - test: it's useful to have this separate from dev deps in the olddeps job
@@ -267,10 +267,10 @@ all = [
 
 [tool.poetry.dev-dependencies]
 ## We pin black so that our tests don't start failing on new releases.
-isort = "==5.10.1"
-black = "==22.3.0"
+isort = ">=5.10.1"
+black = ">=22.3.0"
 flake8-comprehensions = "*"
-flake8-bugbear = "==21.3.2"
+flake8-bugbear = ">=21.3.2"
 flake8 = "*"
 
 # Typechecking
@@ -296,11 +296,11 @@ parameterized = ">=0.7.4"
 idna = ">=2.5"
 
 # The following are used by the release script
-click = "==8.1.3"
+click = ">=8.1.3"
 # GitPython was == 3.1.14; bumped to 3.1.20, the first release with type hints.
 GitPython = ">=3.1.20"
-commonmark = "==0.9.1"
-pygithub = "==1.55"
+commonmark = ">=0.9.1"
+pygithub = ">=1.55"
 # The following are executed as commands by the release script.
 twine = "*"
 # Towncrier min version comes from #3425. Rationale unclear.
diff --git a/synapse/config/cache.py b/synapse/config/cache.py
index 2db8cfb005..eb4194a5a9 100644
--- a/synapse/config/cache.py
+++ b/synapse/config/cache.py
@@ -159,7 +159,7 @@ class CacheConfig(Config):
 
         self.track_memory_usage = cache_config.get("track_memory_usage", False)
         if self.track_memory_usage:
-            check_requirements("cache_memory")
+            check_requirements("cache-memory")
 
         expire_caches = cache_config.get("expire_caches", True)
         cache_entry_ttl = cache_config.get("cache_entry_ttl", "30m")
diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index f9a49451d8..4009add01d 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import Any
+from typing import Any, Optional
 
 import attr
 
@@ -120,3 +120,8 @@ class ExperimentalConfig(Config):
 
         # MSC3874: Filtering /messages with rel_types / not_rel_types.
         self.msc3874_enabled: bool = experimental.get("msc3874_enabled", False)
+
+        # MSC3886: Simple client rendezvous capability
+        self.msc3886_endpoint: Optional[str] = experimental.get(
+            "msc3886_endpoint", None
+        )
diff --git a/synapse/config/server.py b/synapse/config/server.py
index f2353ce5fb..ec46ca63ad 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -207,6 +207,9 @@ class HttpListenerConfig:
     additional_resources: Dict[str, dict] = attr.Factory(dict)
     tag: Optional[str] = None
     request_id_header: Optional[str] = None
+    # If true, the listener will return CORS response headers compatible with MSC3886:
+    # https://github.com/matrix-org/matrix-spec-proposals/pull/3886
+    experimental_cors_msc3886: bool = False
 
 
 @attr.s(slots=True, frozen=True, auto_attribs=True)
@@ -935,6 +938,7 @@ def parse_listener_def(num: int, listener: Any) -> ListenerConfig:
             additional_resources=listener.get("additional_resources", {}),
             tag=listener.get("tag"),
             request_id_header=listener.get("request_id_header"),
+            experimental_cors_msc3886=listener.get("experimental_cors_msc3886", False),
         )
 
     return ListenerConfig(port, bind_addresses, listener_type, tls, http_config)
diff --git a/synapse/event_auth.py b/synapse/event_auth.py
index c7d5ef92fc..bab31e33c5 100644
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -15,7 +15,18 @@
 
 import logging
 import typing
-from typing import Any, Collection, Dict, Iterable, List, Optional, Set, Tuple, Union
+from typing import (
+    Any,
+    Collection,
+    Dict,
+    Iterable,
+    List,
+    Mapping,
+    Optional,
+    Set,
+    Tuple,
+    Union,
+)
 
 from canonicaljson import encode_canonical_json
 from signedjson.key import decode_verify_key_bytes
@@ -134,6 +145,7 @@ def validate_event_for_room_version(event: "EventBase") -> None:
 async def check_state_independent_auth_rules(
     store: _EventSourceStore,
     event: "EventBase",
+    batched_auth_events: Optional[Mapping[str, "EventBase"]] = None,
 ) -> None:
     """Check that an event complies with auth rules that are independent of room state
 
@@ -143,6 +155,8 @@ async def check_state_independent_auth_rules(
     Args:
         store: the datastore; used to fetch the auth events for validation
         event: the event being checked.
+        batched_auth_events: if the event being authed is part of a batch, any events
+            from the same batch that may be necessary to auth the current event
 
     Raises:
         AuthError if the checks fail
@@ -162,6 +176,9 @@ async def check_state_independent_auth_rules(
         redact_behaviour=EventRedactBehaviour.as_is,
         allow_rejected=True,
     )
+    if batched_auth_events:
+        auth_events.update(batched_auth_events)
+
     room_id = event.room_id
     auth_dict: MutableStateMap[str] = {}
     expected_auth_types = auth_types_for_event(event.room_version, event)
diff --git a/synapse/events/snapshot.py b/synapse/events/snapshot.py
index d3c8083e4a..1c0e96bec7 100644
--- a/synapse/events/snapshot.py
+++ b/synapse/events/snapshot.py
@@ -65,7 +65,8 @@ class EventContext:
             None does not necessarily mean that ``state_group`` does not have
             a prev_group!
 
-            If the event is a state event, this is normally the same as ``prev_group``.
+            If the event is a state event, this is normally the same as
+            ``state_group_before_event``.
 
             If ``state_group`` is None (ie, the event is an outlier), ``prev_group``
             will always also be ``None``.
diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index f9cc5bddbc..c597639a7f 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -937,7 +937,10 @@ class DeviceListUpdater:
         # Check if we are partially joining any rooms. If so we need to store
         # all device list updates so that we can handle them correctly once we
         # know who is in the room.
-        partial_rooms = await self.store.get_partial_state_rooms_and_servers()
+        # TODO(faster joins): this fetches and processes a bunch of data that we don't
+        # use. Could be replaced by a tighter query e.g.
+        #   SELECT EXISTS(SELECT 1 FROM partial_state_rooms)
+        partial_rooms = await self.store.get_partial_state_room_resync_info()
         if partial_rooms:
             await self.store.add_remote_device_list_to_pending(
                 user_id,
diff --git a/synapse/handlers/event_auth.py b/synapse/handlers/event_auth.py
index 8249ca1ed2..3bbad0271b 100644
--- a/synapse/handlers/event_auth.py
+++ b/synapse/handlers/event_auth.py
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-from typing import TYPE_CHECKING, Collection, List, Optional, Union
+from typing import TYPE_CHECKING, Collection, List, Mapping, Optional, Union
 
 from synapse import event_auth
 from synapse.api.constants import (
@@ -29,7 +29,6 @@ from synapse.event_auth import (
 )
 from synapse.events import EventBase
 from synapse.events.builder import EventBuilder
-from synapse.events.snapshot import EventContext
 from synapse.types import StateMap, get_domain_from_id
 
 if TYPE_CHECKING:
@@ -51,12 +50,21 @@ class EventAuthHandler:
     async def check_auth_rules_from_context(
         self,
         event: EventBase,
-        context: EventContext,
+        batched_auth_events: Optional[Mapping[str, EventBase]] = None,
     ) -> None:
-        """Check an event passes the auth rules at its own auth events"""
-        await check_state_independent_auth_rules(self._store, event)
+        """Check an event passes the auth rules at its own auth events
+        Args:
+            event: event to be authed
+            batched_auth_events: if the event being authed is part of a batch, any events
+            from the same batch that may be necessary to auth the current event
+        """
+        await check_state_independent_auth_rules(
+            self._store, event, batched_auth_events
+        )
         auth_event_ids = event.auth_event_ids()
         auth_events_by_id = await self._store.get_events(auth_event_ids)
+        if batched_auth_events:
+            auth_events_by_id.update(batched_auth_events)
         check_state_dependent_auth_rules(event, auth_events_by_id.values())
 
     def compute_auth_events(
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 5f7e0a1f79..275a37a575 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -632,6 +632,7 @@ class FederationHandler:
                     room_id=room_id,
                     servers=ret.servers_in_room,
                     device_lists_stream_id=self.store.get_device_stream_token(),
+                    joined_via=origin,
                 )
 
             try:
@@ -941,7 +942,7 @@ class FederationHandler:
 
         # The remote hasn't signed it yet, obviously. We'll do the full checks
         # when we get the event back in `on_send_join_request`
-        await self._event_auth_handler.check_auth_rules_from_context(event, context)
+        await self._event_auth_handler.check_auth_rules_from_context(event)
         return event
 
     async def on_invite_request(
@@ -1122,7 +1123,7 @@ class FederationHandler:
         try:
             # The remote hasn't signed it yet, obviously. We'll do the full checks
             # when we get the event back in `on_send_leave_request`
-            await self._event_auth_handler.check_auth_rules_from_context(event, context)
+            await self._event_auth_handler.check_auth_rules_from_context(event)
         except AuthError as e:
             logger.warning("Failed to create new leave %r because %s", event, e)
             raise e
@@ -1181,7 +1182,7 @@ class FederationHandler:
         try:
             # The remote hasn't signed it yet, obviously. We'll do the full checks
             # when we get the event back in `on_send_knock_request`
-            await self._event_auth_handler.check_auth_rules_from_context(event, context)
+            await self._event_auth_handler.check_auth_rules_from_context(event)
         except AuthError as e:
             logger.warning("Failed to create new knock %r because %s", event, e)
             raise e
@@ -1347,9 +1348,7 @@ class FederationHandler:
 
             try:
                 validate_event_for_room_version(event)
-                await self._event_auth_handler.check_auth_rules_from_context(
-                    event, context
-                )
+                await self._event_auth_handler.check_auth_rules_from_context(event)
             except AuthError as e:
                 logger.warning("Denying new third party invite %r because %s", event, e)
                 raise e
@@ -1399,7 +1398,7 @@ class FederationHandler:
 
         try:
             validate_event_for_room_version(event)
-            await self._event_auth_handler.check_auth_rules_from_context(event, context)
+            await self._event_auth_handler.check_auth_rules_from_context(event)
         except AuthError as e:
             logger.warning("Denying third party invite %r because %s", event, e)
             raise e
@@ -1615,13 +1614,13 @@ class FederationHandler:
         """Resumes resyncing of all partial-state rooms after a restart."""
         assert not self.config.worker.worker_app
 
-        partial_state_rooms = await self.store.get_partial_state_rooms_and_servers()
-        for room_id, servers_in_room in partial_state_rooms.items():
+        partial_state_rooms = await self.store.get_partial_state_room_resync_info()
+        for room_id, resync_info in partial_state_rooms.items():
             run_as_background_process(
                 desc="sync_partial_state_room",
                 func=self._sync_partial_state_room,
-                initial_destination=None,
-                other_destinations=servers_in_room,
+                initial_destination=resync_info.joined_via,
+                other_destinations=resync_info.servers_in_room,
                 room_id=room_id,
             )
 
@@ -1650,28 +1649,12 @@ class FederationHandler:
         #   really leave, that might mean we have difficulty getting the room state over
         #   federation.
         #   https://github.com/matrix-org/synapse/issues/12802
-        #
-        # TODO(faster_joins): we need some way of prioritising which homeservers in
-        #   `other_destinations` to try first, otherwise we'll spend ages trying dead
-        #   homeservers for large rooms.
-        #   https://github.com/matrix-org/synapse/issues/12999
-
-        if initial_destination is None and len(other_destinations) == 0:
-            raise ValueError(
-                f"Cannot resync state of {room_id}: no destinations provided"
-            )
 
         # Make an infinite iterator of destinations to try. Once we find a working
         # destination, we'll stick with it until it flakes.
-        destinations: Collection[str]
-        if initial_destination is not None:
-            # Move `initial_destination` to the front of the list.
-            destinations = list(other_destinations)
-            if initial_destination in destinations:
-                destinations.remove(initial_destination)
-            destinations = [initial_destination] + destinations
-        else:
-            destinations = other_destinations
+        destinations = _prioritise_destinations_for_partial_state_resync(
+            initial_destination, other_destinations, room_id
+        )
         destination_iter = itertools.cycle(destinations)
 
         # `destination` is the current remote homeserver we're pulling from.
@@ -1769,3 +1752,29 @@ class FederationHandler:
                             room_id,
                             destination,
                         )
+
+
+def _prioritise_destinations_for_partial_state_resync(
+    initial_destination: Optional[str],
+    other_destinations: Collection[str],
+    room_id: str,
+) -> Collection[str]:
+    """Work out the order in which we should ask servers to resync events.
+
+    If an `initial_destination` is given, it takes top priority. Otherwise
+    all servers are treated equally.
+
+    :raises ValueError: if no destination is provided at all.
+    """
+    if initial_destination is None and len(other_destinations) == 0:
+        raise ValueError(f"Cannot resync state of {room_id}: no destinations provided")
+
+    if initial_destination is None:
+        return other_destinations
+
+    # Move `initial_destination` to the front of the list.
+    destinations = list(other_destinations)
+    if initial_destination in destinations:
+        destinations.remove(initial_destination)
+    destinations = [initial_destination] + destinations
+    return destinations
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 4e55ebba0b..15b828dd74 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -1360,8 +1360,16 @@ class EventCreationHandler:
             else:
                 try:
                     validate_event_for_room_version(event)
+                    # If we are persisting a batch of events the event(s) needed to auth the
+                    # current event may be part of the batch and will not be in the DB yet
+                    event_id_to_event = {e.event_id: e for e, _ in events_and_context}
+                    batched_auth_events = {}
+                    for event_id in event.auth_event_ids():
+                        auth_event = event_id_to_event.get(event_id)
+                        if auth_event:
+                            batched_auth_events[event_id] = auth_event
                     await self._event_auth_handler.check_auth_rules_from_context(
-                        event, context
+                        event, batched_auth_events
                     )
                 except AuthError as err:
                     logger.warning("Denying new event %r because %s", event, err)
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 4e1aacb408..638f54051a 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -229,9 +229,7 @@ class RoomCreationHandler:
             },
         )
         validate_event_for_room_version(tombstone_event)
-        await self._event_auth_handler.check_auth_rules_from_context(
-            tombstone_event, tombstone_context
-        )
+        await self._event_auth_handler.check_auth_rules_from_context(tombstone_event)
 
         # Upgrade the room
         #
diff --git a/synapse/handlers/sso.py b/synapse/handlers/sso.py
index e035677b8a..5943f08e91 100644
--- a/synapse/handlers/sso.py
+++ b/synapse/handlers/sso.py
@@ -874,7 +874,7 @@ class SsoHandler:
         )
 
     async def handle_terms_accepted(
-        self, request: Request, session_id: str, terms_version: str
+        self, request: SynapseRequest, session_id: str, terms_version: str
     ) -> None:
         """Handle a request to the new-user 'consent' endpoint
 
diff --git a/synapse/http/server.py b/synapse/http/server.py
index bcbfac2c9f..b26e34bceb 100644
--- a/synapse/http/server.py
+++ b/synapse/http/server.py
@@ -19,6 +19,7 @@ import logging
 import types
 import urllib
 from http import HTTPStatus
+from http.client import FOUND
 from inspect import isawaitable
 from typing import (
     TYPE_CHECKING,
@@ -339,7 +340,7 @@ class _AsyncResource(resource.Resource, metaclass=abc.ABCMeta):
 
             return callback_return
 
-        _unrecognised_request_handler(request)
+        return _unrecognised_request_handler(request)
 
     @abc.abstractmethod
     def _send_response(
@@ -598,7 +599,7 @@ class RootRedirect(resource.Resource):
 class OptionsResource(resource.Resource):
     """Responds to OPTION requests for itself and all children."""
 
-    def render_OPTIONS(self, request: Request) -> bytes:
+    def render_OPTIONS(self, request: SynapseRequest) -> bytes:
         request.setResponseCode(204)
         request.setHeader(b"Content-Length", b"0")
 
@@ -763,7 +764,7 @@ def respond_with_json(
 
 
 def respond_with_json_bytes(
-    request: Request,
+    request: SynapseRequest,
     code: int,
     json_bytes: bytes,
     send_cors: bool = False,
@@ -859,7 +860,7 @@ def _write_bytes_to_request(request: Request, bytes_to_write: bytes) -> None:
     _ByteProducer(request, bytes_generator)
 
 
-def set_cors_headers(request: Request) -> None:
+def set_cors_headers(request: SynapseRequest) -> None:
     """Set the CORS headers so that javascript running in a web browsers can
     use this API
 
@@ -870,10 +871,20 @@ def set_cors_headers(request: Request) -> None:
     request.setHeader(
         b"Access-Control-Allow-Methods", b"GET, HEAD, POST, PUT, DELETE, OPTIONS"
     )
-    request.setHeader(
-        b"Access-Control-Allow-Headers",
-        b"X-Requested-With, Content-Type, Authorization, Date",
-    )
+    if request.experimental_cors_msc3886:
+        request.setHeader(
+            b"Access-Control-Allow-Headers",
+            b"X-Requested-With, Content-Type, Authorization, Date, If-Match, If-None-Match",
+        )
+        request.setHeader(
+            b"Access-Control-Expose-Headers",
+            b"ETag, Location, X-Max-Bytes",
+        )
+    else:
+        request.setHeader(
+            b"Access-Control-Allow-Headers",
+            b"X-Requested-With, Content-Type, Authorization, Date",
+        )
 
 
 def set_corp_headers(request: Request) -> None:
@@ -942,10 +953,25 @@ def set_clickjacking_protection_headers(request: Request) -> None:
     request.setHeader(b"Content-Security-Policy", b"frame-ancestors 'none';")
 
 
-def respond_with_redirect(request: Request, url: bytes) -> None:
-    """Write a 302 response to the request, if it is still alive."""
+def respond_with_redirect(
+    request: SynapseRequest, url: bytes, statusCode: int = FOUND, cors: bool = False
+) -> None:
+    """
+    Write a 302 (or other specified status code) response to the request, if it is still alive.
+
+    Args:
+        request: The http request to respond to.
+        url: The URL to redirect to.
+        statusCode: The HTTP status code to use for the redirect (defaults to 302).
+        cors: Whether to set CORS headers on the response.
+    """
     logger.debug("Redirect to %s", url.decode("utf-8"))
-    request.redirect(url)
+
+    if cors:
+        set_cors_headers(request)
+
+    request.setResponseCode(statusCode)
+    request.setHeader(b"location", url)
     finish_request(request)
 
 
diff --git a/synapse/http/site.py b/synapse/http/site.py
index 55a6afce35..3dbd541fed 100644
--- a/synapse/http/site.py
+++ b/synapse/http/site.py
@@ -82,6 +82,7 @@ class SynapseRequest(Request):
         self.reactor = site.reactor
         self._channel = channel  # this is used by the tests
         self.start_time = 0.0
+        self.experimental_cors_msc3886 = site.experimental_cors_msc3886
 
         # The requester, if authenticated. For federation requests this is the
         # server name, for client requests this is the Requester object.
@@ -622,6 +623,8 @@ class SynapseSite(Site):
 
         request_id_header = config.http_options.request_id_header
 
+        self.experimental_cors_msc3886 = config.http_options.experimental_cors_msc3886
+
         def request_factory(channel: HTTPChannel, queued: bool) -> Request:
             return request_class(
                 channel,
diff --git a/synapse/rest/__init__.py b/synapse/rest/__init__.py
index 9a2ab99ede..28542cd774 100644
--- a/synapse/rest/__init__.py
+++ b/synapse/rest/__init__.py
@@ -44,6 +44,7 @@ from synapse.rest.client import (
     receipts,
     register,
     relations,
+    rendezvous,
     report_event,
     room,
     room_batch,
@@ -132,3 +133,4 @@ class ClientRestResource(JsonResource):
         # unstable
         mutual_rooms.register_servlets(hs, client_resource)
         login_token_request.register_servlets(hs, client_resource)
+        rendezvous.register_servlets(hs, client_resource)
diff --git a/synapse/rest/client/rendezvous.py b/synapse/rest/client/rendezvous.py
new file mode 100644
index 0000000000..89176b1ffa
--- /dev/null
+++ b/synapse/rest/client/rendezvous.py
@@ -0,0 +1,74 @@
+# Copyright 2022 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+from http.client import TEMPORARY_REDIRECT
+from typing import TYPE_CHECKING, Optional
+
+from synapse.http.server import HttpServer, respond_with_redirect
+from synapse.http.servlet import RestServlet
+from synapse.http.site import SynapseRequest
+from synapse.rest.client._base import client_patterns
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+logger = logging.getLogger(__name__)
+
+
+class RendezvousServlet(RestServlet):
+    """
+    This is a placeholder implementation of [MSC3886](https://github.com/matrix-org/matrix-spec-proposals/pull/3886)
+    simple client rendezvous capability that is used by the "Sign in with QR" functionality.
+
+    This implementation only serves as a 307 redirect to a configured server rather than being a full implementation.
+
+    A module that implements the full functionality is available at: https://pypi.org/project/matrix-http-rendezvous-synapse/.
+
+    Request:
+
+    POST /rendezvous HTTP/1.1
+    Content-Type: ...
+
+    ...
+
+    Response:
+
+    HTTP/1.1 307
+    Location: <configured endpoint>
+    """
+
+    PATTERNS = client_patterns(
+        "/org.matrix.msc3886/rendezvous$", releases=[], v1=False, unstable=True
+    )
+
+    def __init__(self, hs: "HomeServer"):
+        super().__init__()
+        redirection_target: Optional[str] = hs.config.experimental.msc3886_endpoint
+        assert (
+            redirection_target is not None
+        ), "Servlet is only registered if there is a redirection target"
+        self.endpoint = redirection_target.encode("utf-8")
+
+    async def on_POST(self, request: SynapseRequest) -> None:
+        respond_with_redirect(
+            request, self.endpoint, statusCode=TEMPORARY_REDIRECT, cors=True
+        )
+
+    # PUT, GET and DELETE are not implemented as they should be fulfilled by the redirect target.
+
+
+def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
+    if hs.config.experimental.msc3886_endpoint is not None:
+        RendezvousServlet(hs).register(http_server)
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index 4b87ee978a..9b1b72c68a 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -116,6 +116,9 @@ class VersionsRestServlet(RestServlet):
                     "org.matrix.msc3881": self.config.experimental.msc3881_enabled,
                     # Adds support for filtering /messages by event relation.
                     "org.matrix.msc3874": self.config.experimental.msc3874_enabled,
+                    # Adds support for simple HTTP rendezvous as per MSC3886
+                    "org.matrix.msc3886": self.config.experimental.msc3886_endpoint
+                    is not None,
                 },
             },
         )
diff --git a/synapse/rest/key/v2/local_key_resource.py b/synapse/rest/key/v2/local_key_resource.py
index 0c9f042c84..095993415c 100644
--- a/synapse/rest/key/v2/local_key_resource.py
+++ b/synapse/rest/key/v2/local_key_resource.py
@@ -20,9 +20,9 @@ from signedjson.sign import sign_json
 from unpaddedbase64 import encode_base64
 
 from twisted.web.resource import Resource
-from twisted.web.server import Request
 
 from synapse.http.server import respond_with_json_bytes
+from synapse.http.site import SynapseRequest
 from synapse.types import JsonDict
 
 if TYPE_CHECKING:
@@ -99,7 +99,7 @@ class LocalKey(Resource):
             json_object = sign_json(json_object, self.config.server.server_name, key)
         return json_object
 
-    def render_GET(self, request: Request) -> Optional[int]:
+    def render_GET(self, request: SynapseRequest) -> Optional[int]:
         time_now = self.clock.time_msec()
         # Update the expiry time if less than half the interval remains.
         if time_now + self.config.key.key_refresh_interval / 2 > self.valid_until_ts:
diff --git a/synapse/rest/synapse/client/new_user_consent.py b/synapse/rest/synapse/client/new_user_consent.py
index 1c1c7b3613..22784157e6 100644
--- a/synapse/rest/synapse/client/new_user_consent.py
+++ b/synapse/rest/synapse/client/new_user_consent.py
@@ -20,6 +20,7 @@ from synapse.api.errors import SynapseError
 from synapse.handlers.sso import get_username_mapping_session_cookie_from_request
 from synapse.http.server import DirectServeHtmlResource, respond_with_html
 from synapse.http.servlet import parse_string
+from synapse.http.site import SynapseRequest
 from synapse.types import UserID
 from synapse.util.templates import build_jinja_env
 
@@ -88,7 +89,7 @@ class NewUserConsentResource(DirectServeHtmlResource):
         html = template.render(template_params)
         respond_with_html(request, 200, html)
 
-    async def _async_render_POST(self, request: Request) -> None:
+    async def _async_render_POST(self, request: SynapseRequest) -> None:
         try:
             session_id = get_username_mapping_session_cookie_from_request(request)
         except SynapseError as e:
diff --git a/synapse/rest/well_known.py b/synapse/rest/well_known.py
index 6f7ac54c65..e2174fdfea 100644
--- a/synapse/rest/well_known.py
+++ b/synapse/rest/well_known.py
@@ -18,6 +18,7 @@ from twisted.web.resource import Resource
 from twisted.web.server import Request
 
 from synapse.http.server import set_cors_headers
+from synapse.http.site import SynapseRequest
 from synapse.types import JsonDict
 from synapse.util import json_encoder
 from synapse.util.stringutils import parse_server_name
@@ -63,7 +64,7 @@ class ClientWellKnownResource(Resource):
         Resource.__init__(self)
         self._well_known_builder = WellKnownBuilder(hs)
 
-    def render_GET(self, request: Request) -> bytes:
+    def render_GET(self, request: SynapseRequest) -> bytes:
         set_cors_headers(request)
         r = self._well_known_builder.get_well_known()
         if not r:
diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index 7bb21f8f81..4717c9728a 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -1658,7 +1658,7 @@ class DatabasePool:
             table: string giving the table name
             keyvalues: dict of column names and values to select the row with
             retcol: string giving the name of the column to return
-            allow_none: If true, return None instead of failing if the SELECT
+            allow_none: If true, return None instead of raising StoreError if the SELECT
                 statement returns no rows
             desc: description of the transaction, for logging and metrics
         """
diff --git a/synapse/storage/databases/main/devices.py b/synapse/storage/databases/main/devices.py
index 18358eca46..830b076a32 100644
--- a/synapse/storage/databases/main/devices.py
+++ b/synapse/storage/databases/main/devices.py
@@ -539,9 +539,11 @@ class DeviceWorkerStore(RoomMemberWorkerStore, EndToEndKeyWorkerStore):
                     "device_id": device_id,
                     "prev_id": [prev_id] if prev_id else [],
                     "stream_id": stream_id,
-                    "org.matrix.opentracing_context": opentracing_context,
                 }
 
+                if opentracing_context != "{}":
+                    result["org.matrix.opentracing_context"] = opentracing_context
+
                 prev_id = stream_id
 
                 if device is not None:
@@ -549,7 +551,11 @@ class DeviceWorkerStore(RoomMemberWorkerStore, EndToEndKeyWorkerStore):
                     if keys:
                         result["keys"] = keys
 
-                    device_display_name = device.display_name
+                    device_display_name = None
+                    if (
+                        self.hs.config.federation.allow_device_name_lookup_over_federation
+                    ):
+                        device_display_name = device.display_name
                     if device_display_name:
                         result["device_display_name"] = device_display_name
                 else:
diff --git a/synapse/storage/databases/main/event_push_actions.py b/synapse/storage/databases/main/event_push_actions.py
index f070e6e88a..b283ab0f9c 100644
--- a/synapse/storage/databases/main/event_push_actions.py
+++ b/synapse/storage/databases/main/event_push_actions.py
@@ -294,6 +294,44 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
             self._background_backfill_thread_id,
         )
 
+        # Indexes which will be used to quickly make the thread_id column non-null.
+        self.db_pool.updates.register_background_index_update(
+            "event_push_actions_thread_id_null",
+            index_name="event_push_actions_thread_id_null",
+            table="event_push_actions",
+            columns=["thread_id"],
+            where_clause="thread_id IS NULL",
+        )
+        self.db_pool.updates.register_background_index_update(
+            "event_push_summary_thread_id_null",
+            index_name="event_push_summary_thread_id_null",
+            table="event_push_summary",
+            columns=["thread_id"],
+            where_clause="thread_id IS NULL",
+        )
+
+        # Check ASAP (and then later, every 1s) to see if we have finished
+        # background updates the event_push_actions and event_push_summary tables.
+        self._clock.call_later(0.0, self._check_event_push_backfill_thread_id)
+        self._event_push_backfill_thread_id_done = False
+
+    @wrap_as_background_process("check_event_push_backfill_thread_id")
+    async def _check_event_push_backfill_thread_id(self) -> None:
+        """
+        Has thread_id finished backfilling?
+
+        If not, we need to just-in-time update it so the queries work.
+        """
+        done = await self.db_pool.updates.has_completed_background_update(
+            "event_push_backfill_thread_id"
+        )
+
+        if done:
+            self._event_push_backfill_thread_id_done = True
+        else:
+            # Reschedule to run.
+            self._clock.call_later(15.0, self._check_event_push_backfill_thread_id)
+
     async def _background_backfill_thread_id(
         self, progress: JsonDict, batch_size: int
     ) -> int:
@@ -526,6 +564,25 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
             (ReceiptTypes.READ, ReceiptTypes.READ_PRIVATE),
         )
 
+        # First ensure that the existing rows have an updated thread_id field.
+        if not self._event_push_backfill_thread_id_done:
+            txn.execute(
+                """
+                UPDATE event_push_summary
+                SET thread_id = ?
+                WHERE room_id = ? AND user_id = ? AND thread_id is NULL
+                """,
+                (MAIN_TIMELINE, room_id, user_id),
+            )
+            txn.execute(
+                """
+                UPDATE event_push_actions
+                SET thread_id = ?
+                WHERE room_id = ? AND user_id = ? AND thread_id is NULL
+                """,
+                (MAIN_TIMELINE, room_id, user_id),
+            )
+
         # First we pull the counts from the summary table.
         #
         # We check that `last_receipt_stream_ordering` matches the stream ordering of the
@@ -1341,6 +1398,25 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
                 (room_id, user_id, stream_ordering, *thread_args),
             )
 
+            # First ensure that the existing rows have an updated thread_id field.
+            if not self._event_push_backfill_thread_id_done:
+                txn.execute(
+                    """
+                    UPDATE event_push_summary
+                    SET thread_id = ?
+                    WHERE room_id = ? AND user_id = ? AND thread_id is NULL
+                    """,
+                    (MAIN_TIMELINE, room_id, user_id),
+                )
+                txn.execute(
+                    """
+                    UPDATE event_push_actions
+                    SET thread_id = ?
+                    WHERE room_id = ? AND user_id = ? AND thread_id is NULL
+                    """,
+                    (MAIN_TIMELINE, room_id, user_id),
+                )
+
             # Fetch the notification counts between the stream ordering of the
             # latest receipt and what was previously summarised.
             unread_counts = self._get_notif_unread_count_for_user_room(
@@ -1475,6 +1551,19 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
             rotate_to_stream_ordering: The new maximum event stream ordering to summarise.
         """
 
+        # Ensure that any new actions have an updated thread_id.
+        if not self._event_push_backfill_thread_id_done:
+            txn.execute(
+                """
+                UPDATE event_push_actions
+                SET thread_id = ?
+                WHERE ? < stream_ordering AND stream_ordering <= ? AND thread_id IS NULL
+                """,
+                (MAIN_TIMELINE, old_rotate_stream_ordering, rotate_to_stream_ordering),
+            )
+
+        # XXX Do we need to update summaries here too?
+
         # Calculate the new counts that should be upserted into event_push_summary
         sql = """
             SELECT user_id, room_id, thread_id,
@@ -1537,6 +1626,20 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
 
         logger.info("Rotating notifications, handling %d rows", len(summaries))
 
+        # Ensure that any updated threads have the proper thread_id.
+        if not self._event_push_backfill_thread_id_done:
+            txn.execute_batch(
+                """
+                UPDATE event_push_summary
+                SET thread_id = ?
+                WHERE room_id = ? AND user_id = ? AND thread_id is NULL
+                """,
+                [
+                    (MAIN_TIMELINE, room_id, user_id)
+                    for user_id, room_id, _ in summaries
+                ],
+            )
+
         self.db_pool.simple_upsert_many_txn(
             txn,
             table="event_push_summary",
diff --git a/synapse/storage/databases/main/events_worker.py b/synapse/storage/databases/main/events_worker.py
index 7bc7f2f33e..69fea452ad 100644
--- a/synapse/storage/databases/main/events_worker.py
+++ b/synapse/storage/databases/main/events_worker.py
@@ -1971,12 +1971,17 @@ class EventsWorkerStore(SQLBaseStore):
 
         Args:
             room_id: room where the event lives
-            event_id: event to check
+            event: event to check (can't be an `outlier`)
 
         Returns:
             Boolean indicating whether it's an extremity
         """
 
+        assert not event.internal_metadata.is_outlier(), (
+            "is_event_next_to_backward_gap(...) can't be used with `outlier` events. "
+            "This function relies on `event_backward_extremities` which won't be filled in for `outliers`."
+        )
+
         def is_event_next_to_backward_gap_txn(txn: LoggingTransaction) -> bool:
             # If the event in question has any of its prev_events listed as a
             # backward extremity, it's next to a gap.
@@ -2026,12 +2031,17 @@ class EventsWorkerStore(SQLBaseStore):
 
         Args:
             room_id: room where the event lives
-            event_id: event to check
+            event: event to check (can't be an `outlier`)
 
         Returns:
             Boolean indicating whether it's an extremity
         """
 
+        assert not event.internal_metadata.is_outlier(), (
+            "is_event_next_to_forward_gap(...) can't be used with `outlier` events. "
+            "This function relies on `event_edges` and `event_forward_extremities` which won't be filled in for `outliers`."
+        )
+
         def is_event_next_to_gap_txn(txn: LoggingTransaction) -> bool:
             # If the event in question is a forward extremity, we will just
             # consider any potential forward gap as not a gap since it's one of
@@ -2112,13 +2122,33 @@ class EventsWorkerStore(SQLBaseStore):
             The closest event_id otherwise None if we can't find any event in
             the given direction.
         """
+        if direction == "b":
+            # Find closest event *before* a given timestamp. We use descending
+            # (which gives values largest to smallest) because we want the
+            # largest possible timestamp *before* the given timestamp.
+            comparison_operator = "<="
+            order = "DESC"
+        else:
+            # Find closest event *after* a given timestamp. We use ascending
+            # (which gives values smallest to largest) because we want the
+            # closest possible timestamp *after* the given timestamp.
+            comparison_operator = ">="
+            order = "ASC"
 
-        sql_template = """
+        sql_template = f"""
             SELECT event_id FROM events
             LEFT JOIN rejections USING (event_id)
             WHERE
-                origin_server_ts %s ?
-                AND room_id = ?
+                room_id = ?
+                AND origin_server_ts {comparison_operator} ?
+                /**
+                 * Make sure the event isn't an `outlier` because we have no way
+                 * to later check whether it's next to a gap. `outliers` do not
+                 * have entries in the `event_edges`, `event_forward_extremeties`,
+                 * and `event_backward_extremities` tables to check against
+                 * (used by `is_event_next_to_backward_gap` and `is_event_next_to_forward_gap`).
+                 */
+                AND NOT outlier
                 /* Make sure event is not rejected */
                 AND rejections.event_id IS NULL
             /**
@@ -2128,27 +2158,14 @@ class EventsWorkerStore(SQLBaseStore):
              * Finally, we can tie-break based on when it was received on the server
              * (`stream_ordering`).
              */
-            ORDER BY origin_server_ts %s, depth %s, stream_ordering %s
+            ORDER BY origin_server_ts {order}, depth {order}, stream_ordering {order}
             LIMIT 1;
         """
 
         def get_event_id_for_timestamp_txn(txn: LoggingTransaction) -> Optional[str]:
-            if direction == "b":
-                # Find closest event *before* a given timestamp. We use descending
-                # (which gives values largest to smallest) because we want the
-                # largest possible timestamp *before* the given timestamp.
-                comparison_operator = "<="
-                order = "DESC"
-            else:
-                # Find closest event *after* a given timestamp. We use ascending
-                # (which gives values smallest to largest) because we want the
-                # closest possible timestamp *after* the given timestamp.
-                comparison_operator = ">="
-                order = "ASC"
-
             txn.execute(
-                sql_template % (comparison_operator, order, order, order),
-                (timestamp, room_id),
+                sql_template,
+                (room_id, timestamp),
             )
             row = txn.fetchone()
             if row:
diff --git a/synapse/storage/databases/main/room.py b/synapse/storage/databases/main/room.py
index e41c99027a..7d97f8f60e 100644
--- a/synapse/storage/databases/main/room.py
+++ b/synapse/storage/databases/main/room.py
@@ -97,6 +97,12 @@ class RoomSortOrder(Enum):
     STATE_EVENTS = "state_events"
 
 
+@attr.s(slots=True, frozen=True, auto_attribs=True)
+class PartialStateResyncInfo:
+    joined_via: Optional[str]
+    servers_in_room: List[str] = attr.ib(factory=list)
+
+
 class RoomWorkerStore(CacheInvalidationWorkerStore):
     def __init__(
         self,
@@ -1160,17 +1166,29 @@ class RoomWorkerStore(CacheInvalidationWorkerStore):
             desc="get_partial_state_servers_at_join",
         )
 
-    async def get_partial_state_rooms_and_servers(
+    async def get_partial_state_room_resync_info(
         self,
-    ) -> Mapping[str, Collection[str]]:
-        """Get all rooms containing events with partial state, and the servers known
-        to be in the room.
+    ) -> Mapping[str, PartialStateResyncInfo]:
+        """Get all rooms containing events with partial state, and the information
+        needed to restart a "resync" of those rooms.
 
         Returns:
             A dictionary of rooms with partial state, with room IDs as keys and
             lists of servers in rooms as values.
         """
-        room_servers: Dict[str, List[str]] = {}
+        room_servers: Dict[str, PartialStateResyncInfo] = {}
+
+        rows = await self.db_pool.simple_select_list(
+            table="partial_state_rooms",
+            keyvalues={},
+            retcols=("room_id", "joined_via"),
+            desc="get_server_which_served_partial_join",
+        )
+
+        for row in rows:
+            room_id = row["room_id"]
+            joined_via = row["joined_via"]
+            room_servers[room_id] = PartialStateResyncInfo(joined_via=joined_via)
 
         rows = await self.db_pool.simple_select_list(
             "partial_state_rooms_servers",
@@ -1182,7 +1200,15 @@ class RoomWorkerStore(CacheInvalidationWorkerStore):
         for row in rows:
             room_id = row["room_id"]
             server_name = row["server_name"]
-            room_servers.setdefault(room_id, []).append(server_name)
+            entry = room_servers.get(room_id)
+            if entry is None:
+                # There is a foreign key constraint which enforces that every room_id in
+                # partial_state_rooms_servers appears in partial_state_rooms. So we
+                # expect `entry` to be non-null. (This reasoning fails if we've
+                # partial-joined between the two SELECTs, but this is unlikely to happen
+                # in practice.)
+                continue
+            entry.servers_in_room.append(server_name)
 
         return room_servers
 
@@ -1827,6 +1853,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
         room_id: str,
         servers: Collection[str],
         device_lists_stream_id: int,
+        joined_via: str,
     ) -> None:
         """Mark the given room as containing events with partial state.
 
@@ -1842,6 +1869,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
             servers: other servers known to be in the room
             device_lists_stream_id: the device_lists stream ID at the time when we first
                 joined the room.
+            joined_via: the server name we requested a partial join from.
         """
         await self.db_pool.runInteraction(
             "store_partial_state_room",
@@ -1849,6 +1877,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
             room_id,
             servers,
             device_lists_stream_id,
+            joined_via,
         )
 
     def _store_partial_state_room_txn(
@@ -1857,6 +1886,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
         room_id: str,
         servers: Collection[str],
         device_lists_stream_id: int,
+        joined_via: str,
     ) -> None:
         DatabasePool.simple_insert_txn(
             txn,
@@ -1866,6 +1896,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
                 "device_lists_stream_id": device_lists_stream_id,
                 # To be updated later once the join event is persisted.
                 "join_event_id": None,
+                "joined_via": joined_via,
             },
         )
         DatabasePool.simple_insert_many_txn(
diff --git a/synapse/storage/schema/main/delta/73/06thread_notifications_backfill.sql b/synapse/storage/schema/main/delta/73/06thread_notifications_backfill.sql
deleted file mode 100644
index 0ffde9bbeb..0000000000
--- a/synapse/storage/schema/main/delta/73/06thread_notifications_backfill.sql
+++ /dev/null
@@ -1,29 +0,0 @@
-/* Copyright 2022 The Matrix.org Foundation C.I.C
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
--- Forces the background updates from 06thread_notifications.sql to run in the
--- foreground as code will now require those to be "done".
-
-DELETE FROM background_updates WHERE update_name = 'event_push_backfill_thread_id';
-
--- Overwrite any null thread_id columns.
-UPDATE event_push_actions_staging SET thread_id = 'main' WHERE thread_id IS NULL;
-UPDATE event_push_actions SET thread_id = 'main' WHERE thread_id IS NULL;
-UPDATE event_push_summary SET thread_id = 'main' WHERE thread_id IS NULL;
-
--- Do not run the event_push_summary_unique_index job if it is pending; the
--- thread_id field will be made required.
-DELETE FROM background_updates WHERE update_name = 'event_push_summary_unique_index';
-DROP INDEX IF EXISTS event_push_summary_unique_index;
diff --git a/synapse/storage/schema/main/delta/73/06thread_notifications_thread_id_idx.sql b/synapse/storage/schema/main/delta/73/06thread_notifications_thread_id_idx.sql
new file mode 100644
index 0000000000..8b3c636594
--- /dev/null
+++ b/synapse/storage/schema/main/delta/73/06thread_notifications_thread_id_idx.sql
@@ -0,0 +1,23 @@
+/* Copyright 2022 The Matrix.org Foundation C.I.C
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+-- Allow there to be multiple summaries per user/room.
+DROP INDEX IF EXISTS event_push_summary_unique_index;
+
+INSERT INTO background_updates (ordering, update_name, progress_json, depends_on) VALUES
+  (7306, 'event_push_actions_thread_id_null', '{}', 'event_push_backfill_thread_id');
+
+INSERT INTO background_updates (ordering, update_name, progress_json, depends_on) VALUES
+  (7306, 'event_push_summary_thread_id_null', '{}', 'event_push_backfill_thread_id');
diff --git a/synapse/storage/schema/main/delta/73/07thread_notifications_not_null.sql.sqlite b/synapse/storage/schema/main/delta/73/07thread_notifications_not_null.sql.sqlite
deleted file mode 100644
index 5322ad77a4..0000000000
--- a/synapse/storage/schema/main/delta/73/07thread_notifications_not_null.sql.sqlite
+++ /dev/null
@@ -1,101 +0,0 @@
-/* Copyright 2022 The Matrix.org Foundation C.I.C
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
--- SQLite doesn't support modifying columns to an existing table, so it must
--- be recreated.
-
--- Create the new tables.
-CREATE TABLE event_push_actions_staging_new (
-    event_id TEXT NOT NULL,
-    user_id TEXT NOT NULL,
-    actions TEXT NOT NULL,
-    notif SMALLINT NOT NULL,
-    highlight SMALLINT NOT NULL,
-    unread SMALLINT,
-    thread_id TEXT NOT NULL,
-    inserted_ts BIGINT
-);
-
-CREATE TABLE event_push_actions_new (
-    room_id TEXT NOT NULL,
-    event_id TEXT NOT NULL,
-    user_id TEXT NOT NULL,
-    profile_tag VARCHAR(32),
-    actions TEXT NOT NULL,
-    topological_ordering BIGINT,
-    stream_ordering BIGINT,
-    notif SMALLINT,
-    highlight SMALLINT,
-    unread SMALLINT,
-    thread_id TEXT NOT NULL,
-    CONSTRAINT event_id_user_id_profile_tag_uniqueness UNIQUE (room_id, event_id, user_id, profile_tag)
-);
-
-CREATE TABLE event_push_summary_new (
-    user_id TEXT NOT NULL,
-    room_id TEXT NOT NULL,
-    notif_count BIGINT NOT NULL,
-    stream_ordering BIGINT NOT NULL,
-    unread_count BIGINT,
-    last_receipt_stream_ordering BIGINT,
-    thread_id TEXT NOT NULL
-);
-
--- Swap the indexes.
-DROP INDEX IF EXISTS event_push_actions_staging_id;
-CREATE INDEX event_push_actions_staging_id ON event_push_actions_staging_new(event_id);
-
-DROP INDEX IF EXISTS event_push_actions_room_id_user_id;
-DROP INDEX IF EXISTS event_push_actions_rm_tokens;
-DROP INDEX IF EXISTS event_push_actions_stream_ordering;
-DROP INDEX IF EXISTS event_push_actions_u_highlight;
-DROP INDEX IF EXISTS event_push_actions_highlights_index;
-CREATE INDEX event_push_actions_room_id_user_id on event_push_actions_new(room_id, user_id);
-CREATE INDEX event_push_actions_rm_tokens on event_push_actions_new( user_id, room_id, topological_ordering, stream_ordering );
-CREATE INDEX event_push_actions_stream_ordering on event_push_actions_new( stream_ordering, user_id );
-CREATE INDEX event_push_actions_u_highlight ON event_push_actions_new (user_id, stream_ordering);
-CREATE INDEX event_push_actions_highlights_index ON event_push_actions_new (user_id, room_id, topological_ordering, stream_ordering);
-
--- Copy the data.
-INSERT INTO event_push_actions_staging_new (event_id, user_id, actions, notif, highlight, unread, thread_id, inserted_ts)
-    SELECT event_id, user_id, actions, notif, highlight, unread, thread_id, inserted_ts
-    FROM event_push_actions_staging;
-
-INSERT INTO event_push_actions_new (room_id, event_id, user_id, profile_tag, actions, topological_ordering, stream_ordering, notif, highlight, unread, thread_id)
-    SELECT room_id, event_id, user_id, profile_tag, actions, topological_ordering, stream_ordering, notif, highlight, unread, thread_id
-    FROM event_push_actions;
-
-INSERT INTO event_push_summary_new (user_id, room_id, notif_count, stream_ordering, unread_count, last_receipt_stream_ordering, thread_id)
-    SELECT user_id, room_id, notif_count, stream_ordering, unread_count, last_receipt_stream_ordering, thread_id
-    FROM event_push_summary;
-
--- Drop the old tables.
-DROP TABLE event_push_actions_staging;
-DROP TABLE event_push_actions;
-DROP TABLE event_push_summary;
-
--- Rename the tables.
-ALTER TABLE event_push_actions_staging_new RENAME TO event_push_actions_staging;
-ALTER TABLE event_push_actions_new RENAME TO event_push_actions;
-ALTER TABLE event_push_summary_new RENAME TO event_push_summary;
-
--- Re-run background updates from 72/02event_push_actions_index.sql and
--- 72/06thread_notifications.sql.
-INSERT INTO background_updates (ordering, update_name, progress_json) VALUES
-  (7307, 'event_push_summary_unique_index2', '{}')
-  ON CONFLICT (update_name) DO NOTHING;
-INSERT INTO background_updates (ordering, update_name, progress_json) VALUES
-  (7307, 'event_push_actions_stream_highlight_index', '{}')
-  ON CONFLICT (update_name) DO NOTHING;
diff --git a/synapse/storage/schema/main/delta/73/07thread_notifications_not_null.sql.postgres b/synapse/storage/schema/main/delta/73/09partial_joined_via_destination.sql
index 33674f8c62..066d602b18 100644
--- a/synapse/storage/schema/main/delta/73/07thread_notifications_not_null.sql.postgres
+++ b/synapse/storage/schema/main/delta/73/09partial_joined_via_destination.sql
@@ -13,7 +13,6 @@
  * limitations under the License.
  */
 
--- The columns can now be made non-nullable.
-ALTER TABLE event_push_actions_staging ALTER COLUMN thread_id SET NOT NULL;
-ALTER TABLE event_push_actions ALTER COLUMN thread_id SET NOT NULL;
-ALTER TABLE event_push_summary ALTER COLUMN thread_id SET NOT NULL;
+-- When we resync partial state, we prioritise doing so using the server we
+-- partial-joined from. To do this we need to record which server that was!
+ALTER TABLE partial_state_rooms ADD COLUMN joined_via TEXT;
diff --git a/tests/logging/test_terse_json.py b/tests/logging/test_terse_json.py
index 96f399b7ab..0b0d8737c1 100644
--- a/tests/logging/test_terse_json.py
+++ b/tests/logging/test_terse_json.py
@@ -153,6 +153,7 @@ class TerseJsonTestCase(LoggerCleanupMixin, TestCase):
         site.site_tag = "test-site"
         site.server_version_string = "Server v1"
         site.reactor = Mock()
+        site.experimental_cors_msc3886 = False
         request = SynapseRequest(FakeChannel(site, None), site)
         # Call requestReceived to finish instantiating the object.
         request.content = BytesIO()
diff --git a/tests/rest/client/test_rendezvous.py b/tests/rest/client/test_rendezvous.py
new file mode 100644
index 0000000000..ad00a476e1
--- /dev/null
+++ b/tests/rest/client/test_rendezvous.py
@@ -0,0 +1,45 @@
+# Copyright 2022 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from twisted.test.proto_helpers import MemoryReactor
+
+from synapse.rest.client import rendezvous
+from synapse.server import HomeServer
+from synapse.util import Clock
+
+from tests import unittest
+from tests.unittest import override_config
+
+endpoint = "/_matrix/client/unstable/org.matrix.msc3886/rendezvous"
+
+
+class RendezvousServletTestCase(unittest.HomeserverTestCase):
+
+    servlets = [
+        rendezvous.register_servlets,
+    ]
+
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
+        self.hs = self.setup_test_homeserver()
+        return self.hs
+
+    def test_disabled(self) -> None:
+        channel = self.make_request("POST", endpoint, {}, access_token=None)
+        self.assertEqual(channel.code, 400)
+
+    @override_config({"experimental_features": {"msc3886_endpoint": "/asd"}})
+    def test_redirect(self) -> None:
+        channel = self.make_request("POST", endpoint, {}, access_token=None)
+        self.assertEqual(channel.code, 307)
+        self.assertEqual(channel.headers.getRawHeaders("Location"), ["/asd"])
diff --git a/tests/rest/client/test_rooms.py b/tests/rest/client/test_rooms.py
index 71b1637be8..716366eb90 100644
--- a/tests/rest/client/test_rooms.py
+++ b/tests/rest/client/test_rooms.py
@@ -39,6 +39,8 @@ from synapse.api.constants import (
 )
 from synapse.api.errors import Codes, HttpResponseException
 from synapse.appservice import ApplicationService
+from synapse.events import EventBase
+from synapse.events.snapshot import EventContext
 from synapse.handlers.pagination import PurgeStatus
 from synapse.rest import admin
 from synapse.rest.client import account, directory, login, profile, register, room, sync
@@ -51,6 +53,7 @@ from tests import unittest
 from tests.http.server._base import make_request_with_cancellation_test
 from tests.storage.test_stream import PaginationTestCase
 from tests.test_utils import make_awaitable
+from tests.test_utils.event_injection import create_event
 
 PATH_PREFIX = b"/_matrix/client/api/v1"
 
@@ -3486,3 +3489,65 @@ class ThreepidInviteTestCase(unittest.HomeserverTestCase):
         )
         self.assertEqual(channel.code, 400)
         self.assertEqual(channel.json_body["errcode"], "M_MISSING_PARAM")
+
+
+class TimestampLookupTestCase(unittest.HomeserverTestCase):
+    servlets = [
+        admin.register_servlets,
+        room.register_servlets,
+        login.register_servlets,
+    ]
+
+    def default_config(self) -> JsonDict:
+        config = super().default_config()
+        config["experimental_features"] = {"msc3030_enabled": True}
+        return config
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self._storage_controllers = self.hs.get_storage_controllers()
+
+        self.room_owner = self.register_user("room_owner", "test")
+        self.room_owner_tok = self.login("room_owner", "test")
+
+    def _inject_outlier(self, room_id: str) -> EventBase:
+        event, _context = self.get_success(
+            create_event(
+                self.hs,
+                room_id=room_id,
+                type="m.test",
+                sender="@test_remote_user:remote",
+            )
+        )
+
+        event.internal_metadata.outlier = True
+        self.get_success(
+            self._storage_controllers.persistence.persist_event(
+                event, EventContext.for_outlier(self._storage_controllers)
+            )
+        )
+        return event
+
+    def test_no_outliers(self) -> None:
+        """
+        Test to make sure `/timestamp_to_event` does not return `outlier` events.
+        We're unable to determine whether an `outlier` is next to a gap so we
+        don't know whether it's actually the closest event. Instead, let's just
+        ignore `outliers` with this endpoint.
+
+        This test is really seeing that we choose the non-`outlier` event behind the
+        `outlier`. Since the gap checking logic considers the latest message in the room
+        as *not* next to a gap, asking over federation does not come into play here.
+        """
+        room_id = self.helper.create_room_as(self.room_owner, tok=self.room_owner_tok)
+
+        outlier_event = self._inject_outlier(room_id)
+
+        channel = self.make_request(
+            "GET",
+            f"/_matrix/client/unstable/org.matrix.msc3030/rooms/{room_id}/timestamp_to_event?dir=b&ts={outlier_event.origin_server_ts}",
+            access_token=self.room_owner_tok,
+        )
+        self.assertEqual(HTTPStatus.OK, channel.code, msg=channel.json_body)
+
+        # Make sure the outlier event is not returned
+        self.assertNotEqual(channel.json_body["event_id"], outlier_event.event_id)
diff --git a/tests/server.py b/tests/server.py
index c447d5e4c4..8b1d186219 100644
--- a/tests/server.py
+++ b/tests/server.py
@@ -266,7 +266,12 @@ class FakeSite:
     site_tag = "test"
     access_logger = logging.getLogger("synapse.access.http.fake")
 
-    def __init__(self, resource: IResource, reactor: IReactorTime):
+    def __init__(
+        self,
+        resource: IResource,
+        reactor: IReactorTime,
+        experimental_cors_msc3886: bool = False,
+    ):
         """
 
         Args:
@@ -274,6 +279,7 @@ class FakeSite:
         """
         self._resource = resource
         self.reactor = reactor
+        self.experimental_cors_msc3886 = experimental_cors_msc3886
 
     def getResourceFor(self, request):
         return self._resource
diff --git a/tests/test_server.py b/tests/test_server.py
index 7c66448245..2d9a0257d4 100644
--- a/tests/test_server.py
+++ b/tests/test_server.py
@@ -222,13 +222,22 @@ class OptionsResourceTests(unittest.TestCase):
         self.resource = OptionsResource()
         self.resource.putChild(b"res", DummyResource())
 
-    def _make_request(self, method: bytes, path: bytes) -> FakeChannel:
+    def _make_request(
+        self, method: bytes, path: bytes, experimental_cors_msc3886: bool = False
+    ) -> FakeChannel:
         """Create a request from the method/path and return a channel with the response."""
         # Create a site and query for the resource.
         site = SynapseSite(
             "test",
             "site_tag",
-            parse_listener_def(0, {"type": "http", "port": 0}),
+            parse_listener_def(
+                0,
+                {
+                    "type": "http",
+                    "port": 0,
+                    "experimental_cors_msc3886": experimental_cors_msc3886,
+                },
+            ),
             self.resource,
             "1.0",
             max_request_body_size=4096,
@@ -239,25 +248,58 @@ class OptionsResourceTests(unittest.TestCase):
         channel = make_request(self.reactor, site, method, path, shorthand=False)
         return channel
 
+    def _check_cors_standard_headers(self, channel: FakeChannel) -> None:
+        # Ensure the correct CORS headers have been added
+        # as per https://spec.matrix.org/v1.4/client-server-api/#web-browser-clients
+        self.assertEqual(
+            channel.headers.getRawHeaders(b"Access-Control-Allow-Origin"),
+            [b"*"],
+            "has correct CORS Origin header",
+        )
+        self.assertEqual(
+            channel.headers.getRawHeaders(b"Access-Control-Allow-Methods"),
+            [b"GET, HEAD, POST, PUT, DELETE, OPTIONS"],  # HEAD isn't in the spec
+            "has correct CORS Methods header",
+        )
+        self.assertEqual(
+            channel.headers.getRawHeaders(b"Access-Control-Allow-Headers"),
+            [b"X-Requested-With, Content-Type, Authorization, Date"],
+            "has correct CORS Headers header",
+        )
+
+    def _check_cors_msc3886_headers(self, channel: FakeChannel) -> None:
+        # Ensure the correct CORS headers have been added
+        # as per https://github.com/matrix-org/matrix-spec-proposals/blob/hughns/simple-rendezvous-capability/proposals/3886-simple-rendezvous-capability.md#cors
+        self.assertEqual(
+            channel.headers.getRawHeaders(b"Access-Control-Allow-Origin"),
+            [b"*"],
+            "has correct CORS Origin header",
+        )
+        self.assertEqual(
+            channel.headers.getRawHeaders(b"Access-Control-Allow-Methods"),
+            [b"GET, HEAD, POST, PUT, DELETE, OPTIONS"],  # HEAD isn't in the spec
+            "has correct CORS Methods header",
+        )
+        self.assertEqual(
+            channel.headers.getRawHeaders(b"Access-Control-Allow-Headers"),
+            [
+                b"X-Requested-With, Content-Type, Authorization, Date, If-Match, If-None-Match"
+            ],
+            "has correct CORS Headers header",
+        )
+        self.assertEqual(
+            channel.headers.getRawHeaders(b"Access-Control-Expose-Headers"),
+            [b"ETag, Location, X-Max-Bytes"],
+            "has correct CORS Expose Headers header",
+        )
+
     def test_unknown_options_request(self) -> None:
         """An OPTIONS requests to an unknown URL still returns 204 No Content."""
         channel = self._make_request(b"OPTIONS", b"/foo/")
         self.assertEqual(channel.code, 204)
         self.assertNotIn("body", channel.result)
 
-        # Ensure the correct CORS headers have been added
-        self.assertTrue(
-            channel.headers.hasHeader(b"Access-Control-Allow-Origin"),
-            "has CORS Origin header",
-        )
-        self.assertTrue(
-            channel.headers.hasHeader(b"Access-Control-Allow-Methods"),
-            "has CORS Methods header",
-        )
-        self.assertTrue(
-            channel.headers.hasHeader(b"Access-Control-Allow-Headers"),
-            "has CORS Headers header",
-        )
+        self._check_cors_standard_headers(channel)
 
     def test_known_options_request(self) -> None:
         """An OPTIONS requests to an known URL still returns 204 No Content."""
@@ -265,19 +307,17 @@ class OptionsResourceTests(unittest.TestCase):
         self.assertEqual(channel.code, 204)
         self.assertNotIn("body", channel.result)
 
-        # Ensure the correct CORS headers have been added
-        self.assertTrue(
-            channel.headers.hasHeader(b"Access-Control-Allow-Origin"),
-            "has CORS Origin header",
-        )
-        self.assertTrue(
-            channel.headers.hasHeader(b"Access-Control-Allow-Methods"),
-            "has CORS Methods header",
-        )
-        self.assertTrue(
-            channel.headers.hasHeader(b"Access-Control-Allow-Headers"),
-            "has CORS Headers header",
+        self._check_cors_standard_headers(channel)
+
+    def test_known_options_request_msc3886(self) -> None:
+        """An OPTIONS requests to an known URL still returns 204 No Content."""
+        channel = self._make_request(
+            b"OPTIONS", b"/res/", experimental_cors_msc3886=True
         )
+        self.assertEqual(channel.code, 204)
+        self.assertNotIn("body", channel.result)
+
+        self._check_cors_msc3886_headers(channel)
 
     def test_unknown_request(self) -> None:
         """A non-OPTIONS request to an unknown URL should 404."""