FA-76163 / Chat ordering and read receipts / Member archive

Decide which messages start a new visual group: after system · case 03

The first user message after a system notice is glued to the group before the notice.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

messages are ascending {author, ts, kind}. A message shows a header (starts a group) when it is the first message, when it or the previous message is a system message, when the author changes, when more than 300 seconds passed since the previous message, or when the UTC day changes. Result: one boolean per message.

Why this case matters

Compact chat layouts hide repeated avatars; wrong grouping attributes messages to the wrong person or time.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
after a system message	`[true, true, false]`	`[true, true, true]`	Failed

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