Support MSC4446: allow moving fully read markers backwards#19663
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SpiritCroc wants to merge 9 commits into
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Support MSC4446: allow moving fully read markers backwards#19663SpiritCroc wants to merge 9 commits into
SpiritCroc wants to merge 9 commits into
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MadLittleMods
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This was referenced Apr 8, 2026
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Pull request overview
This PR implements MSC4446 support in Synapse, allowing clients to move the m.fully_read marker backwards when explicitly opted-in and when the experimental feature flag is enabled.
Changes:
- Add an experimental config flag (
msc4446_enabled) and expose it via/_matrix/client/versionsas an unstable feature. - Extend the read-marker and receipt endpoints to accept
com.beeper.allow_backward(boolean) to allow backwards movement for fully-read markers when enabled. - Add client REST tests covering default (forwards-only) behavior, opt-in backwards behavior, and invalid usage.
Reviewed changes
Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| tests/rest/client/test_receipts.py | Adds tests for backwards movement behavior via the receipts endpoint, including feature-flag gating and invalid usage. |
| tests/rest/client/test_read_marker.py | Adds tests for backwards movement behavior via /read_markers, plus versions endpoint tests for the unstable feature flag. |
| synapse/rest/client/versions.py | Advertises com.beeper.msc4446 in unstable_features based on config. |
| synapse/rest/client/receipts.py | Parses/validates com.beeper.allow_backward (when enabled) and forwards it to the read-marker handler for fully-read receipts. |
| synapse/rest/client/read_marker.py | Parses/validates com.beeper.allow_backward (when enabled) and forwards it to the read-marker handler for m.fully_read. |
| synapse/handlers/read_marker.py | Adds allow_backward support to permit setting m.fully_read to an older event when opted-in. |
| synapse/config/experimental.py | Introduces msc4446_enabled experimental config option. |
| changelog.d/19663.feature | Adds Towncrier newsfragment for the feature. |
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| """Updates the read marker for a given user in a given room if the event ID given | ||
| is ahead in the stream relative to the current read marker. |
anoadragon453
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Jun 29, 2026
anoadragon453
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anoadragon453
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Sorry for the glacial review time. We're burning down our backlog as a team currently.
Just a couple small things. Otherwise looks pretty good to go!
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| # MSC4446: Allow moving the fully read marker backwards. | ||
| self.msc4446_enabled: bool = experimental.get("msc4446_enabled", False) |
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Could you create an experimental feature issue so we can track this implementation going forwards?
Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Conflicts: synapse/rest/client/versions.py
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MSC4446
Pull Request Checklist
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