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[codex] Fix partial world-local exclusive writes - #2296
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🦋 Changeset detectedLatest commit: 89971e0 The changes in this PR will be included in the next version bump. This PR includes changesets to release 18 packages
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📊 Benchmark Results
workflow with no steps💻 Local Development
workflow with 1 step💻 Local Development
workflow with 10 sequential steps💻 Local Development
workflow with 25 sequential steps💻 Local Development
workflow with 50 sequential steps💻 Local Development
Promise.all with 10 concurrent steps💻 Local Development
Promise.all with 25 concurrent steps💻 Local Development
Promise.all with 50 concurrent steps💻 Local Development
Promise.race with 10 concurrent steps💻 Local Development
Promise.race with 25 concurrent steps💻 Local Development
Promise.race with 50 concurrent steps💻 Local Development
workflow with 10 sequential data payload steps (10KB)💻 Local Development
workflow with 25 sequential data payload steps (10KB)💻 Local Development
workflow with 50 sequential data payload steps (10KB)💻 Local Development
workflow with 10 concurrent data payload steps (10KB)💻 Local Development
workflow with 25 concurrent data payload steps (10KB)💻 Local Development
workflow with 50 concurrent data payload steps (10KB)💻 Local Development
Stream Benchmarks(includes TTFB metrics)workflow with stream💻 Local Development
stream pipeline with 5 transform steps (1MB)💻 Local Development
10 parallel streams (1MB each)💻 Local Development
fan-out fan-in 10 streams (1MB each)💻 Local Development
SummaryFastest Framework by WorldWinner determined by most benchmark wins
Fastest World by FrameworkWinner determined by most benchmark wins
Column Definitions
Worlds:
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🧪 E2E Test Results❌ Some tests failed Summary
❌ Failed Tests▲ Vercel Production (10 failed)astro (1 failed):
example (1 failed):
fastify (1 failed):
hono (1 failed):
nextjs-turbopack (1 failed):
nitro (2 failed):
nuxt (2 failed):
vite (1 failed):
Details by Category❌ ▲ Vercel Production
✅ 💻 Local Development
✅ 📦 Local Production
✅ 🐘 Local Postgres
✅ 🪟 Windows
✅ 📋 Other
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Pull request overview
This PR fixes a race in @workflow/world-local where writeExclusive() could expose a partially written destination file to concurrent readers by switching to a “write temp file → hard-link publish” flow, and adds tests to validate publication visibility and first-writer-wins behavior.
Changes:
- Update
writeExclusive()to publish via a fully-written temp file and an atomic hard-link into the final path. - Add deterministic tests ensuring destinations aren’t visible mid-write and that only one concurrent writer wins.
- Add a patch changeset and refresh related inline comments in the storage layer.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| packages/world-local/src/storage/events-storage.ts | Updates commentary to reflect the publish semantics used by writeExclusive(). |
| packages/world-local/src/fs.ts | Implements atomic publish for exclusive writes using temp file + hard-link. |
| packages/world-local/src/fs.test.ts | Adds deterministic coverage for publication visibility and concurrent writer winner selection. |
| .changeset/atomic-runs-publish.md | Patch changeset documenting the fix for partial visibility during exclusive writes. |
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TooTallNate
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Jun 8, 2026
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Approve — clean fix for a real partial-read race, with one defensive nit
The bug is real and the fix is the right shape:
- Before:
fs.writeFile(filePath, data, { flag: 'wx' })writes directly to the destination. The exclusive create guarantees only one writer wins, but the destination path becomes visible during the write — a concurrentruns.get()can read partial JSON and fail withSyntaxError: Unexpected end of JSON input. - After: write to
${filePath}.tmp.${ulid()}first, thenfs.link()to the destination. Link creation is atomic at the OS level and fails withEEXISTif another writer already published.
This matches the established pattern in the sibling write() function (which uses fs.rename() for the overwriting variant); the only difference here is link vs rename to preserve first-writer-wins semantics.
Test design is excellent
The first test simulates a slow write by mocking fs.writeFile to pause mid-write, then attempts to read the destination. With the OLD code, the read returns partial content '{"value":'; with the NEW code, the read returns ENOENT (destination doesn't exist until link succeeds). The post-PR file content is exactly the full payload. Verified regression: I temporarily reverted just the fs.ts change and reran the test — got expected ENOENT, received '{"value":' exactly as the test asserts.
The second test (16 concurrent writers) confirms:
- Exactly one returns
true(the winner) - The final file content matches one specific writer's value
- The directory has only
exclusive.json(no orphaned temp files)
That last assertion is the cleanup check, which catches the finally block actually running.
What I verified locally
pnpm turbo run build --filter @workflow/world-local✓pnpm --filter @workflow/world-local test✓ (368 tests pass)- Reverted the fix and confirmed the new partial-visibility test fails as expected → restored the fix, all green
CI
5 failures, all pre-existing on main's baseline:
- Vercel Prod E2E (nextjs-turbopack, hono, fastify) — same flakes seen on main's recent runs
- Local Postgres canary (nextjs-turbopack) — Next.js canary tracks; the latest main canary baseline shows similar instability
- E2E Required Check — cascading
Nothing PR-specific.
One defensive nit (non-blocker, inline)
Copilot caught a small defensive-coding miss: the finally block unconditionally unlinks tempPath, but if the fs.writeFile(tempPath, ..., { flag: 'wx' }) itself fails with EEXIST (vanishingly rare ULID collision or a stale temp from a crashed process), the unlink would delete someone else's temp file. The existing write() function already handles this with a tempFileCreated flag — same pattern would close the gap here. Inline comment with the snippet.
Practical risk is essentially zero (2^-40 collision probability), but matching the surrounding pattern is essentially free.
Bottom line
Solid fix for a real race that surfaces as SyntaxError: Unexpected end of JSON input in production. The hard-link-after-write pattern is the canonical atomic-publish primitive for "first writer wins" semantics on POSIX filesystems.
Approving.
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* fix(world-local): publish exclusive files atomically * fix(world-local): guard temp cleanup Signed-off-by: Pranay Prakash <pranay.gp@gmail.com>
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* fix(world-local): publish exclusive files atomically * fix(world-local): guard temp cleanup Signed-off-by: Pranay Prakash <pranay.gp@gmail.com> Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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…-attributes-client * origin/main: (32 commits) feat(core): add optional namespace for queue topic prefix (#2305) [web-shared] Show precise durations in the new trace viewer (#2335) Validate unique workflow step IDs at build time (#2018) Move run attributes into their own detail card (#2327) [core] Forward-port stream reconnect to getReadable level (#2318) [docs] Add "Step executed multiple times" error page (#2310) Fix flickering on the detail panel when navigating the trace viewer (#2325) Version Packages (beta) (#2254) Patch vulnerable package dependencies (#2301) Deprecate DurableAgent and update it with WorkflowAgent in v5 docs (#2285) [codex] Fix partial world-local exclusive writes (#2296) [world-vercel] Validate ref resolve responses before use (#2035) fix: bump devalue to 5.8.1 (#2292) Handle lazy stream key request failures (#2257) fix(docs): declare Nitro auto-import globals for code samples (#2290) [core] Preserve event-log order in hook-vs-sleep replay races (#2171) (#2185) docs: add nitro changelog (#2232) fix(next): always apply turbopack content condition regardless of builder mode (#2253) Update @vercel/queue from 0.2.1 to 0.3.0 (#2255) [nest] Use AST-based CommonJS import rewriting (#2080) ... # Conflicts: # packages/world-local/src/storage/events-storage.ts
pranaygp added a commit
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…hook-ready * origin-https/main: (119 commits) fix: settle aborted parallel steps before completing abortParallelWorkflow (#2244) Add native v4 workflow attribute events (#2226) Version Packages (beta) (#2326) [ci] Fix flaky windows unit tests (#2359) Capture Vercel runtime logs when e2e Vercel Prod lanes fail (#2356) Fix e2e failure reporting under vitest 4 and preserve fetch error causes (#2355) [core] Fix process crash from rejected waitUntil promises (#2336) [core] Remove duplicate `waitUntil` for suspension handler async operations (#2345) Prevent local tests from hanging (#2338) feat(core): add optional namespace for queue topic prefix (#2305) [web-shared] Show precise durations in the new trace viewer (#2335) Validate unique workflow step IDs at build time (#2018) Move run attributes into their own detail card (#2327) [core] Forward-port stream reconnect to getReadable level (#2318) [docs] Add "Step executed multiple times" error page (#2310) Fix flickering on the detail panel when navigating the trace viewer (#2325) Version Packages (beta) (#2254) Patch vulnerable package dependencies (#2301) Deprecate DurableAgent and update it with WorkflowAgent in v5 docs (#2285) [codex] Fix partial world-local exclusive writes (#2296) ... # Conflicts: # packages/core/src/runtime.ts # packages/core/src/runtime/suspension-handler.ts
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Summary
@workflow/world-localRoot cause
writeExclusive()previously calledfs.writeFile()directly on the final path with thewxflag. The exclusive create prevented another writer from winning, but the final path became visible before the JSON body was fully written. A concurrentruns.get()could therefore read an empty or truncated run file and fail withSyntaxError: Unexpected end of JSON input.The new implementation writes and closes a temporary file first, then hard-links it into the final path. Link creation is atomic and returns
EEXISTwhen another writer has already published the destination.Verification
pnpm --filter @workflow/world-local test(368 tests)pnpm --filter @workflow/world-local typecheckpnpm turbo run build --filter=@workflow/world-local...