Narrow the outbox watermark fence to its allocation-proof core - #44
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The watermarker's exclusive advisory fence covered lease renewal, configuration, the fenced read/publish, commit, observations, and the durable heartbeat, so a queued exclusive waiter convoyed shared outbox writers behind the whole step. The exclusive section now covers exactly what the C-S2 sequence-allocation proof requires -- the candidate watermark read and publication in one fenced transaction, committed atomically with the lock release -- while lease work happens before acquisition (revalidated inside the fenced transaction), observations operate on in-memory state after commit, and the operation heartbeat runs post-commit through the pool. Each moved operation carries its fence-free argument in the review record. The convoy regression uses deterministic lock gates: a leading shared writer, a queued exclusive watermarker, and a queued shared writer, then the dangerous gap interleaving -- a late lower sequence held uncommitted while a higher shared writer commits during the unfenced heartbeat -- proving safe_seq stays below the gap until the next fenced step. Also fixed en route: a post-commit heartbeat failure no longer suppresses the committed progress observation, and a canceled heartbeat provably leaves a complete watermark with no leaked fence. Every existing stream, outbox, and streamclient test passes unchanged. Fixes #36 Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Fixes #36 — the exclusive fence now covers only what the C-S2 allocation proof requires (fenced candidate read + publication + atomic commit/release); lease renewal, config, observations, and the durable heartbeat moved out, each with a stated fence-free argument (table in the review record). Convoy regression uses deterministic lock gates including the dangerous lower-uncommitted/higher-committed gap during the unfenced heartbeat —
safe_seqprovably stays below the gap. Bonus fixes: committed progress no longer suppressed by heartbeat failure; canceled heartbeats leave no leaked fence. All existing stream/outbox/streamclient tests unchanged.Built and adversarially reviewed by paired Codex sol-xhigh agents in a dedicated worktree (parallel batch #33–#38). Full gate green locally.
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