FA-76263 / Chat ordering and read receipts / Member archive

Assign idempotent per-conversation sequence numbers: idempotency scope · case 03

A second sender, or the same sender in another conversation, who happens to reuse a nonce gets the other message's seq.

Member previewVariant 3 · 3 implementations · 6 checks per implementation

Case contract

requests are [conv, sender, nonce] in arrival order; members maps conv -> member list. A sender who is not a member gets "forbidden" and consumes nothing. Each conversation numbers accepted messages 1, 2, 3... A retry with the same (conv, sender, nonce) returns the originally assigned seq without consuming a new one.

Why this case matters

Server sequencing is the backbone of chat ordering; idempotency errors create duplicates or gaps.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
nonce reused by another sender	`[1, 1]`	`[1, 2]`	Failed

MEMBER ARCHIVE

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