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Client keep-alive stamps in the memory awaited-action db (the
ActionEvent::ClientKeepAlive path in handle_action_events, and the
initial stamp in try_subscribe) mutate the AwaitedAction in place via
send_if_modified WITHOUT bumping AwaitedActionVersion. Any concurrent
read-modify-write cycle (SimpleSchedulerStateManager borrow() ->
update_awaited_action) that snapshotted the action at version N before
the stamp still passes the version CAS, and send_replace writes the
whole stale snapshot back -- a classic lost update that silently moves
last_client_keepalive_timestamp backwards. The Code::Aborted retry
defense never fires because the version matches. Consequence: the
client-timeout sweep force-fails operations whose clients are alive and
polling ("no more clients listening" DeadlineExceeded), including
operations a client subscribed to moments earlier.
Fix shape: treat the keep-alive stamp as data outside the versioned
snapshot rather than routing it through the versioned update path.
update_awaited_action now merges the stamp forward (monotone max of old
and new) before send_replace, so an accepted stale write can never
revert it. Chosen over version-bumping keep-alives because (1) a bump
would spuriously abort legitimate in-flight worker updates and wake
every changed() subscriber ~every CLIENT_KEEPALIVE_DURATION per client,
(2) it needs no new per-operation state, and (3) it leaves the
AwaitedAction wire/record format and the store/redis backend untouched.
Two deterministic repro tests included; both fail without the one-line
merge and pass with it (verified both directions, 5x each).
Provenance: adversarial review fleet.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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What and why
Lane A stability fix from the findings catalog (see
nativelink-findings-2026-10-05.csvon the
meta/findings-catalog-2026-10-05branch), rebased onto OSS main@bf4b3aa855. This fork PR exists to validate the change on CI that is
representative of upstream PR lanes (public read-only cache, same endpoints)
before any upstream submission.
How was this verified?
The branch carries its own regression tests (fails-without where the fix
class allows it — see the branch's test commits). This PR's purpose is the
full representative CI run; green here rehearses the exact checks an
upstream PR would face.
Risk
Fork-internal validation PR; nothing lands anywhere by merging this. The
underlying fix's risk assessment happens at upstream-submission time.
AI assistance
Agent-assisted pipeline (Claude) for rebase and PR mechanics under my
direction; the fix itself carries verification in its tests.