Add clearSessionRoom function and tests for stale session room handling

[habdelra]

Summary

• Stop repeated realm event broadcast failures caused by stale Matrix session room ids.
• Detect the specific M_FORBIDDEN "realm server not in room" send error during broadcastRealmEvent.
• Clear the stored users.session_room_id for that user/room pair so future index broadcasts stop targeting an invalid room.
• Add regression tests for both the DB helper and the realm-server broadcast cleanup path.
• Register the new realm-server test in the CI shard list.

Problem

After from-scratch indexing, realm-server could try to broadcast incremental index events into per-user session DM rooms that no longer included @realm_server:localhost. Those stale session_room_id values remained in the database, so every later broadcast retried the same dead room and logged repeated 403 M_FORBIDDEN errors.

Fix

When Matrix rejects a send with the specific "user not in room" error, realm-server now treats that room mapping as stale and removes it from the user record. This keeps the existing design intact, where realm events are delivered through per-user session DMs, while preventing endless retries against rooms the service account has already left or lost access to.

[Copilot]

Pull request overview

Fixes repeated 403 M_FORBIDDEN errors when realm-server tries to broadcast realm events to stale Matrix session rooms. When the send fails because the realm server is no longer in the room, the stale session_room_id is cleared from the database.

Changes:

• Added clearSessionRoom DB helper that conditionally nulls out a user's session_room_id when it matches a given room ID.
• Added error detection in broadcastRealmEvent to catch "not in room" Matrix errors and clear the stale session room.
• Added tests for both the DB helper and the broadcast cleanup path, registered in CI.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/runtime-common/db-queries/session-room-queries.ts	New clearSessionRoom function
packages/realm-server/node-realm.ts	Error parsing + stale room cleanup in broadcastRealmEvent
packages/realm-server/tests/session-room-queries-test.ts	Tests for clearSessionRoom
packages/realm-server/tests/node-realm-test.ts	Tests for broadcast stale room handling
packages/realm-server/tests/index.ts	Register new test file
.github/workflows/ci.yaml	Add new test to CI shard list

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[github-actions]

Host Test Results

    1 files      1 suites   2h 29m 19s ⏱️
2 022 tests 2 007 ✅ 15 💤 0 ❌
2 037 runs  2 022 ✅ 15 💤 0 ❌

Results for commit 3caf9b7.

♻️ This comment has been updated with latest results.

[backspace]

The same host test failed on a PR of mine so it seems spurious or flaky 😞

[habdelra]

that test failure should be fixed in main now. if you merge upstream it will pass