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…under a live id ApiWorkerSchedulerImpl::add_worker used LruCache::put, which silently replaced a live entry when a worker re-registered under an existing id. The replaced Worker was dropped together with its running_action_infos: nothing was requeued, the old channel never heard Disconnect, and the gauges were only partially adjusted. Downstream, the replaced worker's operations stayed Executing assigned to the id; when the new incarnation was later evicted its empty list requeued nothing, and the eventual timeout requeued the operation to another worker while the original process might still be running it -- double execution. Now ApiWorkerScheduler::add_worker treats a live entry under the same id exactly like a disconnect before admitting the new incarnation: it goes through immediate_evict_worker, which drains running_action_infos via UpdateOperationType::UpdateWithDisconnect, sends Disconnect on the old channel, and balances the connect/disconnect gauges. A requeue failure is logged and does not block the reconnecting worker. Deterministically reproduced by the DST fuzzer schedule in PR TraceMachina#2831; the new regression test (worker re-registers mid-execution, asserts Disconnect on the old channel, re-dispatch of the same operation to the new channel, and completion) fails on unfixed main. 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.