No significant changes since 1.128.0rc1.

- Add an access token introspection cache to make Matrix Authentication Service integration ([MSC3861](https://github.com/matrix-org/matrix-doc/pull/3861)) more efficient. ([\#18231](https://github.com/element-hq/synapse/issues/18231))
- Add background job to clear unreferenced state groups. ([\#18254](https://github.com/element-hq/synapse/issues/18254))
- Hashes of media files are now tracked by Synapse. Media quarantines will now apply to all files with the same hash. ([\#18277](https://github.com/element-hq/synapse/issues/18277), [\#18302](https://github.com/element-hq/synapse/issues/18302), [\#18296](https://github.com/element-hq/synapse/issues/18296))

- Add index to sliding sync ([MSC4186](https://github.com/matrix-org/matrix-doc/pull/4186)) membership snapshot table, to fix a performance issue. ([\#18074](https://github.com/element-hq/synapse/issues/18074))

- Specify the architecture of installed packages via an APT config option, which is more reliable than appending package names with `:{arch}`. ([\#18271](https://github.com/element-hq/synapse/issues/18271))
- Always specify base image debian versions with a build argument. ([\#18272](https://github.com/element-hq/synapse/issues/18272))
- Allow passing arguments to `start_for_complement.sh` (to be sent to `configure_workers_and_start.py`). ([\#18273](https://github.com/element-hq/synapse/issues/18273))
- Make some improvements to the `prefix-log` script in the workers image. ([\#18274](https://github.com/element-hq/synapse/issues/18274))
- Use `uv pip` to install `supervisor` in the worker image. ([\#18275](https://github.com/element-hq/synapse/issues/18275))
- Avoid needing to download & use `rsync` in a build layer. ([\#18287](https://github.com/element-hq/synapse/issues/18287))

- Fix how to obtain access token and change naming from riot to element ([\#18225](https://github.com/element-hq/synapse/issues/18225))
- Correct a small typo in the SSO mapping providers documentation. ([\#18276](https://github.com/element-hq/synapse/issues/18276))
- Add docs for how to clear out the Poetry wheel cache. ([\#18283](https://github.com/element-hq/synapse/issues/18283))

- Add a column `participant` to `room_memberships` table. ([\#18068](https://github.com/element-hq/synapse/issues/18068))
- Update Poetry to 2.1.1, including updating the lock file version. ([\#18251](https://github.com/element-hq/synapse/issues/18251))
- Pin GitHub Actions dependencies by commit hash. ([\#18255](https://github.com/element-hq/synapse/issues/18255))
- Add DB delta to remove the old state group deletion job. ([\#18284](https://github.com/element-hq/synapse/issues/18284))

* Bump actions/add-to-project from f5473ace9aeee8b97717b281e26980aa5097023f to 280af8ae1f83a494cfad2cb10f02f6d13529caa9. ([\#18303](https://github.com/element-hq/synapse/issues/18303))
* Bump actions/cache from 4.2.2 to 4.2.3. ([\#18266](https://github.com/element-hq/synapse/issues/18266))
* Bump actions/download-artifact from 4.2.0 to 4.2.1. ([\#18268](https://github.com/element-hq/synapse/issues/18268))
* Bump actions/setup-python from 5.4.0 to 5.5.0. ([\#18298](https://github.com/element-hq/synapse/issues/18298))
* Bump actions/upload-artifact from 4.6.1 to 4.6.2. ([\#18304](https://github.com/element-hq/synapse/issues/18304))
* Bump authlib from 1.4.1 to 1.5.1. ([\#18306](https://github.com/element-hq/synapse/issues/18306))
* Bump dawidd6/action-download-artifact from 8 to 9. ([\#18204](https://github.com/element-hq/synapse/issues/18204))
* Bump jinja2 from 3.1.5 to 3.1.6. ([\#18223](https://github.com/element-hq/synapse/issues/18223))
* Bump log from 0.4.26 to 0.4.27. ([\#18267](https://github.com/element-hq/synapse/issues/18267))
* Bump phonenumbers from 8.13.50 to 9.0.2. ([\#18299](https://github.com/element-hq/synapse/issues/18299))
* Bump pygithub from 2.5.0 to 2.6.1. ([\#18243](https://github.com/element-hq/synapse/issues/18243))
* Bump pyo3-log from 0.12.1 to 0.12.2. ([\#18269](https://github.com/element-hq/synapse/issues/18269))
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