FA-76320 / Chat ordering and read receipts / Member archive

Compute a member's visible history and initial read marker: shared history · case 05

Rooms configured to share history with new members still hide everything before the join.

Member previewVariant 5 · 3 implementations · 6 checks per implementation

Case contract

messages are seqs (duplicates possible). A member sees seqs >= join_seq, or all seqs from 1 when the room shares history with new members; after leaving at leave_seq they see nothing after leave_seq (their own leave event included). The initial read marker is join_seq - 1, so only messages from the join onward are unread. Result {visible (sorted, unique), initial_marker}.

Why this case matters

Membership changes decide which history a user may read and where their unread count starts.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
shared history	`{"initial_marker": 2, "visible": [3, 9]}`	`{"initial_marker": 2, "visible": [1, 2, 3, 9]}`	Failed

MEMBER ARCHIVE

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