FA-75868 / Chat ordering and read receipts / Member archive
Advance a stored read marker from a device report: clamp to latest · case 03
A client reporting an optimistic local sequence pushes the marker past messages that have not arrived yet, so they are never counted unread.
Case contract
A report from a device session whose epoch differs from the current epoch (for example a session that predates a "mark unread") is ignored. Otherwise the report is clamped to latest_seq and the marker only moves forward. Result: {marker, broadcast (true only when the marker changed), unread = max(0, latest_seq - marker)}.
Why this case matters
Read markers drive unread badges on every device; regressions or stale sessions resurrect or hide unread messages.
One recorded failure
Sample boundary fixtureThis sample comes from the broken implementation of a controlled reproducer.
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| report beyond latest | {"broadcast": true, "marker": 23, "unread": 0} | {"broadcast": true, "marker": 7, "unread": 0} | Failed |
MEMBER ARCHIVE
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