FA-76077 / Chat ordering and read receipts / Member archive

Page older history with a composite (ts, id) cursor: more flag · case 02

An extra empty page is requested whenever history length is an exact multiple of the page size.

Member previewVariant 2 · 3 implementations · 6 checks per implementation

Case contract

messages are [ts, id] pairs in any order; ordering is by (ts, id). cursor is None or the exclusive [ts, id] of the oldest message already shown. A page holds the newest `limit` messages strictly older than the cursor, in ascending order; next is the [ts, id] of the page's oldest item when older messages remain, else None.

Why this case matters

Infinite-scroll history must neither skip nor duplicate messages that share a timestamp.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
exact multiple	`{"next": [1, "a"], "page": ["a", "b", "c", "d"]}`	`{"next": null, "page": ["a", "b", "c", "d"]}`	Failed

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