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world-local: atomically dedupe duplicate step_created/wait_created events - #1877
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Pull request overview
Fixes a race in @workflow/world-local where concurrent writers could create duplicate step_created / wait_created events (and overwrite entities) when the same correlationId is produced concurrently (notably by the snapshot runtime’s deterministic correlation IDs).
Changes:
- Add an atomic per-
(runId, correlationId)constraint-file claim (viawriteExclusive/O_CREAT|O_EXCL) forstep_created. - Replace
wait_created’s TOCTOU read-then-check with the same atomic constraint-file claim. - Add regression tests covering concurrent duplicates for steps/waits and sequential duplicate steps, plus a changeset for a patch release.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| packages/world-local/src/storage/events-storage.ts | Adds atomic .locks/{steps,waits} constraint-file claims to dedupe concurrent step_created/wait_created. |
| packages/world-local/src/storage.test.ts | Adds regression coverage for concurrent duplicate creation races and sequential duplicate step_created. |
| .changeset/fix-world-local-step-created-race.md | Publishes a patch changeset describing the concurrency fix and behavior change. |
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TooTallNate
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VaguelySerious, ijjk, karthikscale3 and pranaygpApril 30, 2026 08:21
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…-local Concurrent invocations producing identical correlationIds (as the snapshot runtime does by design across replays) previously both succeeded and persisted duplicate events. step_created had no guard at all; wait_created used a TOCTOU read-then-check that allowed both writers through under concurrency. Both now claim a per-(runId, correlationId) constraint file with O_CREAT|O_EXCL before writing, so the loser surfaces as EntityConflictError — which the runtime's dedup catch path already handles.
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This was referenced May 4, 2026
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…ignal * origin/main: [workbench] Add TanStack Start workbench and tests (#1875) Atomically dedupe duplicate step_created/wait_created events in world-local (#1877) Split tarball hosting out of docs into its own project (#1893) Replace fixed-sleep hook waits with event-driven waitForHook helper (#1879)
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…lier-errors-followups * origin-https/main: [workbench] Add TanStack Start workbench and tests (#1875) Atomically dedupe duplicate step_created/wait_created events in world-local (#1877) Split tarball hosting out of docs into its own project (#1893) Replace fixed-sleep hook waits with event-driven waitForHook helper (#1879) # Conflicts: # pnpm-lock.yaml
This was referenced May 4, 2026
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Summary
Fixes a race condition in
@workflow/world-localwhere concurrent invocations producing identicalcorrelationIds forstep_createdorwait_createdevents would both succeed and persist duplicate events in the log.Background
step_createdpreviously had no atomicity guard — two concurrent calls with the samecorrelationIdboth wrote the entity and the event, leaving the second write to silently overwrite the first.wait_createdused a TOCTOU read-then-check pattern: read the existing wait, throw if found, otherwise write. Under concurrency both readers can pass the existence check before either writes.The rest of the runtime already expects
EntityConflictErrorto be thrown on duplicate writes (see theEntityConflictError.is(err)catch path inruntime/snapshot-entrypoint.ts), so the missing guard was a real correctness gap.Fix
Both branches now claim a per-
(runId, correlationId)constraint file under.locks/{steps,waits}/withO_CREAT|O_EXCLsemantics (via the existingwriteExclusivehelper used for hook tokens). The loser surfaces asEntityConflictError.Includes 3 regression tests covering:
step_createdwith same correlationId.wait_createdwith same correlationId (replaces the prior TOCTOU pattern).step_created(existing pass-through behavior preserved).Verification
Extracted from PR #1300 (snapshot-runtime), where this fix originated. The snapshot runtime produces deterministic correlationIds across concurrent VM invocations of the same resumption by design — that path made the dedup gap reliably reproducible — but the fix is also valuable on its own for the replay runtime under any concurrent-create scenario.