Update reverse proxy docs with what we've learned from
https://github.com/element-hq/synapse/pull/17986

Also vice versa and update our nginx config with what I learned from the
reverse proxy docs.

### Pull Request Checklist

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correct
(run the
[linters](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#run-the-linters))

Be able to test `/login/sso/redirect` in Complement

Spawning from
https://github.com/element-hq/sbg/pull/421#discussion_r1854926218 where
we have a proxy that intercepts responses to
`/_matrix/client/v3/login/sso/redirect(/{idpId})` in order to upgrade
them to use OAuth 2.0 Pushed Authorization Requests (PAR). We have some
Complement tests in that codebase that go over this flow and these
changes are required [in order for the URL's to line
up](https://github.com/element-hq/synapse/blob/d648c8ce3f4cbf61191b9f5302e405f7b0288677/synapse/rest/client/login.py#L652-L673).

Signed-off-by: Joe Groocock <me@frebib.net>

If we leave the `.so` in place it causes the tests to fail, as it gets
picked up (instead of the newly built .so) and so fails with mismatched
GLIBC errors.

Sid now defaults to python3.12, and our pinned version of cffi (1.5.1)
does not have wheels for 3.12. This installing cffi to fail as we did
not have the correct libs installed to build from source.

Co-authored-by: Andrew Morgan <andrew@amorgan.xyz>

MSC4115 has now completed FCP, so we can enable it by default and switch
to the stable identifier.

This is an alternative to
https://github.com/matrix-org/matrix-rust-sdk/issues/3340 where we don't
need to change our CI setup too much in the Rust SDK repository, and
still can test MSC3266.

### Pull Request Checklist

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* [x] Pull request is based on the develop branch
* [x] Pull request includes a [changelog
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The entry should:
- Be a short description of your change which makes sense to users.
"Fixed a bug that prevented receiving messages from other servers."
instead of "Moved X method from `EventStore` to `EventWorkerStore`.".
  - Use markdown where necessary, mostly for `code blocks`.
  - End with either a period (.) or an exclamation mark (!).
  - Start with a capital letter.
- Feel free to credit yourself, by adding a sentence "Contributed by
@github_username." or "Contributed by [Your Name]." to the end of the
entry.
* [x] [Code
style](https://element-hq.github.io/synapse/latest/code_style.html) is
correct
(run the
[linters](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#run-the-linters))

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

MSC3967 was updated recently to make it more robust to network failures:

> there is an existing cross-signing master key and it exactly matches
the cross-signing master key provided in the request body. If there are
any additional keys provided in the request (self signing key, user
signing key) they MUST also match the existing keys stored on the
server. In other words, the request contains no new keys. If there are
new keys, UIA MUST be performed.


https://github.com/matrix-org/matrix-spec-proposals/blob/hughns/device-signing-upload-uia/proposals/3967-device-signing-upload-uia.md#proposal

This covers the case where the 200 OK is lost in transit so the client
retries the upload, only to then get UIA'd.

Complement tests: https://github.com/matrix-org/complement/pull/713 -
passing example
https://github.com/element-hq/synapse/actions/runs/7976948122/job/21778795094?pr=16943#step:7:8820

### Pull Request Checklist

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* [x] Pull request is based on the develop branch
* [x] Pull request includes a [changelog
file](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#changelog).
The entry should:
- Be a short description of your change which makes sense to users.
"Fixed a bug that prevented receiving messages from other servers."
instead of "Moved X method from `EventStore` to `EventWorkerStore`.".
  - Use markdown where necessary, mostly for `code blocks`.
  - End with either a period (.) or an exclamation mark (!).
  - Start with a capital letter.
- Feel free to credit yourself, by adding a sentence "Contributed by
@github_username." or "Contributed by [Your Name]." to the end of the
entry.
* [x] [Code
style](https://element-hq.github.io/synapse/latest/code_style.html) is
correct
(run the
[linters](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#run-the-linters)

)

---------

Co-authored-by: reivilibre <oliverw@matrix.org>

Follow on from #17037

Prevent `start_for_complement.sh` from setting `START_POSTGRES` to `false` when it's already set (#16985)

I have a use case where I'd like the Synapse image to start up a
postgres instance that I can use, but don't want to force Synapse to use
postgres as well.

This commit prevents postgres from being started when it has already
been explicitly enabled elsewhere.

Background: we have a `matrixdotorg/synapse-workers` docker image, which
is intended for running multiple workers within the same container. That
image includes a `prefix-log` script which, for each line printed to
stdout or stderr by one of the processes, prepends the name of the
process.

This commit disables buffering in that script, so that lines are logged
quickly after they are printed. This makes it much easier to understand
the output, since they then come out in a natural order.

During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.

Pulled out of #16803 since the drive-by cleanup was maybe not as
drive-by as I had hoped.

<!--
Fixes: # <!-- -->
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Supersedes: # <!-- -->
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Follows: # <!-- -->
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Base: `develop` <!-- git-stack-base-branch:develop -->

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Original commit schedule, with full messages:

<ol>
<li>

Add a --generate-only option 

</li>
</ol>

---------

Signed-off-by: Olivier Wilkinson (reivilibre) <oliverw@matrix.org>

* complement: enable dirty runs

* Add changelog

* Set a low connpool limit when running in Complement

Dirty runs can cause many containers to be running concurrently,
which seems to easily exhaust resources on the host. The increased
speedup from dirty runs also seems to use more db connections on
workers, which are misconfigured currently to have
`SUM(workers * cp_max) > max_connections`, causing
```
FATAL:  sorry, too many clients already
```
which results in tests failing.

* Try p=2 concurrency to restrict slowness of servers which causes partial state join tests to flake

* Debug logging

* Only run flakey tests

* Only adjust connection pool limits in worker mode

* Move cp vars to somewhere where they get executed in CI

* Move cp values back to where they actually work

* Debug logging

* Try p=1 to see if this makes worker mode happier

* Remove debug logging

Enable additional checks & clean-up unneeded configuration.

Unix socket support for `federation` and `client` Listeners has existed now for a little while(since [1.81.0](https://github.com/matrix-org/synapse/pull/15353)

), but there was one last hold out before it could be complete: HTTP Replication communication. This should finish it up. The Listeners would have always worked, but would have had no way to be talked to/at.

---------

Co-authored-by: Eric Eastwood <madlittlemods@gmail.com>
Co-authored-by: Olivier Wilkinson (reivilibre) <oliverw@matrix.org>
Co-authored-by: Eric Eastwood <erice@element.io>

Fix https://github.com/matrix-org/synapse/issues/15836

Remove experimental MSC2716 implementation to incrementally import history into existing rooms (#15748)

Context for why we're removing the implementation:

 - https://github.com/matrix-org/matrix-spec-proposals/pull/2716#issuecomment-1487441010
 - https://github.com/matrix-org/matrix-spec-proposals/pull/2716#issuecomment-1504262734

Anyone wanting to continue MSC2716, should also address these leftover tasks: https://github.com/matrix-org/synapse/issues/10737

Closes https://github.com/matrix-org/synapse/issues/10737 in the fact that it is not longer necessary to track those things.

Bumps library/redis from 6-bullseye to 7-bullseye.

---
updated-dependencies:
- dependency-name: library/redis
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

See https://github.com/matrix-org/synapse/pull/14095#discussion_r990335492

This is useful because when see that a relevant event is an `outlier` or `soft-failed`, then that's a good unexpected indicator explaining why it's not showing up. `filter_events_for_client` is used in `/sync`, `/messages`, `/context` which are all common end-to-end assertion touch points (also notifications, relations).

* Fully qualified docker image names for the main Dockerfile and Complement related.

* Fully qualified docker image names for Dockerfiles associated with building Debian release artifacts.

This one is harder and is separate from the other commit in case it wasn't correct or was unwanted. I decided to
do the expansion on the docker images in the Dockerfile itself, instead of the various source places that build
which distribution that is selected, as it would have been more invasive with the scripts breaking up the string
for tagging and such. This one is untested.

* Changelog

* Update docker/Dockerfile-workers

* Update docker/complement/Dockerfile

---------

Co-authored-by: reivilibre <olivier@librepush.net>