FA-76043 / Chat ordering and read receipts / Member archive
Plan history backfill requests for missing sequences: range close · case 03
Backfill ranges include the first message that was already received.
Case contract
have lists received seqs (unsorted, duplicates possible); horizon is the oldest seq the server still retains; head is the newest known seq. Every seq in [horizon, head] not received is missing; missing seqs are merged into inclusive [start, end] ranges, returned newest first and limited to max_ranges. complete is true only when nothing is missing.
Why this case matters
Chat clients repair gaps after reconnecting; wrong ranges refetch too much or leave holes in the timeline.
One recorded failure
Sample boundary fixtureThis sample comes from the broken implementation of a controlled reproducer.
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| gap before first received | {"complete": false, "fetch": [[10, 12], [5, 8]]} | {"complete": false, "fetch": [[10, 11], [5, 7]]} | Failed |
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