FA-76272 / Chat ordering and read receipts / Member archive

Assign idempotent per-conversation sequence numbers: first sequence · case 02

The first message of a conversation receives seq 0 instead of 1.

Member previewVariant 2 · 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	`[0, 1]`	`[1, 2]`	Failed

MEMBER ARCHIVE

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