FA-76055 / Chat ordering and read receipts / Member archive

Plan history backfill requests for missing sequences: newest first · case 05

Old gaps are backfilled before the recent history the user is looking at.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

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 fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
gap before first received	`{"complete": false, "fetch": [[7, 9], [12, 13]]}`	`{"complete": false, "fetch": [[12, 13], [7, 9]]}`	Failed

MEMBER ARCHIVE

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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