FA-76005 / Chat ordering and read receipts / Member archive

Place the "new messages" divider in a loaded window: no divider sentinel · case 05

When nothing is unread the divider is drawn at the end of the list instead of being omitted.

Member previewVariant 5 · 3 implementations · 6 checks per implementation

Case contract

messages are ascending [seq, author] pairs of the loaded window that starts at window_start. Sending a message implies having read everything before it, so the effective marker is the larger of marker and the highest seq authored by me. The divider goes before the first loaded message after the effective marker not written by me (index, or None). older_unread is true when some unread seq lies before the loaded window (effective marker < window_start - 1).

Why this case matters

The divider tells users where to resume reading; misplacing it hides or repeats unread history.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
all read	`{"index": 2, "older_unread": false}`	`{"index": null, "older_unread": false}`	Failed

MEMBER ARCHIVE

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