Implement max_events per run limit

[shalabhc]

Summary

Enforces the published per-run events limit, which was previously not enforced. The server supplies the limit on the run_started response (separate change); once a run's event log reaches it, the runtime throws MaxEventsExceededError at the top of the replay loop, and the existing terminal-error path records it as run_failed with a new MAX_EVENTS_EXCEEDED code — instead of letting a runaway workflow (e.g. an unbounded step loop) grow the event log without bound.

• Checked after the log is loaded and before runWorkflow schedules more work; deterministic, so it fails without retry/redelivery and is attributed to user code.
• Enforced under both the Vercel World (server-supplied limit) and the Local World (WORKFLOW_MAX_EVENTS).
• Additive and backwards-compatible: older servers/worlds omit the limit ⇒ no enforcement, in either direction.

Testing

• classify-error.test.ts — MaxEventsExceededError classifies as MAX_EVENTS_EXCEEDED.
• describe-error.test.ts — user attribution + hint for the code.
• world-testing E2E — a runaway workflow fails with MAX_EVENTS_EXCEEDED via the in-process Local World (WORKFLOW_MAX_EVENTS=10, turbo disabled), no Docker.

Pairs with the server change: vercel/workflow-server#638

[changeset-bot]

🦋 Changeset detected

Latest commit: f70fea4

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 21 packages

Name	Type
@workflow/errors	Patch
@workflow/core	Patch
@workflow/world	Patch
@workflow/world-vercel	Patch
@workflow/builders	Patch
@workflow/cli	Patch
@workflow/web-shared	Patch
@workflow/web	Patch
workflow	Patch
@workflow/world-local	Patch
@workflow/world-postgres	Patch
@workflow/next	Patch
@workflow/nitro	Patch
@workflow/vitest	Patch
@workflow/world-testing	Patch
@workflow/astro	Patch
@workflow/nest	Patch
@workflow/nuxt	Patch
@workflow/rollup	Patch
@workflow/sveltekit	Patch
@workflow/vite	Patch

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[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
example-nextjs-workflow-webpack	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
example-workflow	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workbench-astro-workflow	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workbench-express-workflow	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workbench-fastify-workflow	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workbench-hono-workflow	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workbench-nestjs-workflow	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workbench-nitro-workflow	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workbench-nuxt-workflow	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workbench-sveltekit-workflow	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workbench-tanstack-start-workflow	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workbench-vite-workflow	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workflow-docs	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workflow-swc-playground	Building	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workflow-tarballs	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm
workflow-web	Ready	Preview, Comment, Open in v0	Jul 21, 2026 8:46pm

[github-actions]

📊 Workflow Benchmarks

commit 81e9dcb · Tue, 21 Jul 2026 21:00:02 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	129 (+16%) 🔻	315 🔴 (+41%) 🔻	373 🔴 (-8.1%)	456 (-13%)	30
TTFS	stream	124 (-8.8%)	206 🔴 (-29%) 💚	227 (-37%) 💚	492 (-39%) 💚	30
TTFS	hook + stream	293 (-17%) 💚	461 🔴 (-9.3%)	586 🔴 (+1.7%)	1378 🔴 (+123%) 🔻	30
STSO	1020 steps (1-20)	196 (+15%)	318 🔴 (+20%) 🔻	364 🔴 (+13%)	743 🔴 (+104%) 🔻	19
STSO	1020 steps (101-120)	244 (+18%) 🔻	356 🔴 (+17%) 🔻	456 🔴 (+33%) 🔻	596 🔴 (+26%) 🔻	19
STSO	1020 steps (1001-1020)	599 (+2.2%)	803 🔴 (+12%)	1015 🔴 (+31%) 🔻	1022 🔴 (+25%) 🔻	19
WO	1020 steps	574390 (+9.0%)	574390 (+9.0%)	574390 (+9.0%)	574390 (+9.0%)	1
SL	stream latency	76 (±0%)	117 🔴 (+13%)	155 🔴 (-6.6%)	228 🔴 (-5.8%)	30

📜 Previous results (8)

f70fea4

Tue, 21 Jul 2026 18:44:53 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	155 (-85%) 💚	300 🔴 (-74%) 💚	383 🔴 (-70%) 💚	431 (-72%) 💚	30
TTFS	stream	154 (-38%) 💚	386 🔴 (-66%) 💚	509 🔴 (-58%) 💚	2386 🔴 (+92%) 🔻	30
TTFS	hook + stream	300 (-76%) 💚	507 🔴 (-65%) 💚	731 🔴 (-51%) 💚	2592 🔴 (+60%) 🔻	30
STSO	1020 steps (1-20)	196 (+8.9%)	325 🔴 (+1.6%)	428 🔴 (+18%) 🔻	453 🔴 (+3.9%)	19
STSO	1020 steps (101-120)	240 (+16%) 🔻	415 🔴 (+28%) 🔻	525 🔴 (+38%) 🔻	1034 🔴 (+106%) 🔻	19
STSO	1020 steps (1001-1020)	620 (+24%) 🔻	731 🔴 (+23%) 🔻	869 🔴 (+35%) 🔻	911 🔴 (+24%) 🔻	19
WO	1020 steps	545430 (+24%) 🔻	545430 (+24%) 🔻	545430 (+24%) 🔻	545430 (+24%) 🔻	1
SL	stream latency	100 (+1.0%)	156 🔴 (-7.1%)	191 🔴 (+3.8%)	2560 🔴 (+1091%) 🔻	30

6d2ded2

Tue, 21 Jul 2026 04:23:07 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	443 (-38%) 💚	1290 🔴 (+20%) 🔻	1307 🔴 (+19%) 🔻	1424 🔴 (-4.2%)	30
TTFS	stream	1209 (+29%) 🔻	1274 🔴 (+23%) 🔻	1286 🔴 (+21%) 🔻	1293 🔴 (+19%) 🔻	30
TTFS	hook + stream	1423 (+19%) 🔻	1545 🔴 (+21%) 🔻	1689 🔴 (+29%) 🔻	3424 🔴 (+140%) 🔻	30
STSO	1020 steps (1-20)	166 (-3.5%)	278 🔴 (+14%)	372 🔴 (+30%) 🔻	435 🔴 (+26%) 🔻	19
STSO	1020 steps (101-120)	180 (-6.3%)	244 🔴 (-7.9%)	323 🔴 (-53%) 💚	360 🔴 (-68%) 💚	19
STSO	1020 steps (1001-1020)	468 (+2.0%)	592 🔴 (+17%) 🔻	724 🔴 (+32%) 🔻	3563 🔴 (+430%) 🔻	19
WO	1020 steps	374542 (-1.1%)	374542 (-1.1%)	374542 (-1.1%)	374542 (-1.1%)	1
SL	stream latency	83 (+1.2%)	142 🔴 (+15%)	158 🔴 (-1.3%)	246 🔴 (+12%)	30

3a9ff12

Tue, 21 Jul 2026 01:06:57 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	233 (-67%) 💚	1275 🔴 (+19%) 🔻	1316 🔴 (+20%) 🔻	1411 🔴 (-5.0%)	30
TTFS	stream	213 (-77%) 💚	1257 🔴 (+21%) 🔻	1278 🔴 (+21%) 🔻	1340 🔴 (+23%) 🔻	30
TTFS	hook + stream	540 (-55%) 💚	1482 🔴 (+16%) 🔻	1516 🔴 (+15%) 🔻	1652 🔴 (+16%) 🔻	30
STSO	1020 steps (1-20)	171 (-0.6%)	283 🔴 (+16%) 🔻	310 🔴 (+8.4%)	316 🔴 (-8.4%)	19
STSO	1020 steps (101-120)	175 (-8.9%)	246 🔴 (-7.2%)	317 🔴 (-54%) 💚	543 🔴 (-52%) 💚	19
STSO	1020 steps (1001-1020)	467 (+1.7%)	571 🔴 (+12%)	585 🔴 (+6.4%)	882 🔴 (+31%) 🔻	19
WO	1020 steps	390362 (+3.0%)	390362 (+3.0%)	390362 (+3.0%)	390362 (+3.0%)	1
SL	stream latency	90 (+9.8%)	145 🔴 (+17%) 🔻	209 🔴 (+31%) 🔻	307 🔴 (+40%) 🔻	30

3f073da

Mon, 20 Jul 2026 20:27:41 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	—	1353 🔴	1398 🔴	1464 🔴	30
TTFS	stream	—	1346 🔴	1405 🔴	1449 🔴	30
TTFS	hook + stream	—	1693 🔴	1707 🔴	1776 🔴	30
STSO	1020 steps (1-20)	—	355 🔴	450 🔴	458 🔴	19
STSO	1020 steps (101-120)	—	306 🔴	366 🔴	402 🔴	19
STSO	1020 steps (1001-1020)	—	611 🔴	701 🔴	728 🔴	19
WO	1020 steps	—	434124	434124	434124	1
SL	stream latency	—	169 🔴	206 🔴	234 🔴	30

8d92b85

Mon, 20 Jul 2026 19:32:09 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	—	1409 🔴	1428 🔴	1586 🔴	30
TTFS	stream	—	1401 🔴	1438 🔴	1978 🔴	30
TTFS	hook + stream	—	1694 🔴	1726 🔴	2009 🔴	30
STSO	1020 steps (1-20)	—	268 🔴	307 🔴	309 🔴	19
STSO	1020 steps (101-120)	—	344 🔴	417 🔴	521 🔴	19
STSO	1020 steps (1001-1020)	—	564 🔴	613 🔴	696 🔴	19
WO	1020 steps	—	414896	414896	414896	1
SL	stream latency	—	192 🔴	231 🔴	300 🔴	30

5062c00

Mon, 20 Jul 2026 18:46:24 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	—	1266 🔴	1279 🔴	1333 🔴	30
TTFS	stream	—	1280 🔴	1290 🔴	1316 🔴	30
TTFS	hook + stream	—	1479 🔴	1522 🔴	1606 🔴	30
STSO	1020 steps (1-20)	—	311 🔴	488 🔴	524 🔴	19
STSO	1020 steps (101-120)	—	332 🔴	429 🔴	638 🔴	19
STSO	1020 steps (1001-1020)	—	561 🔴	669 🔴	674 🔴	19
WO	1020 steps	—	416504	416504	416504	1
SL	stream latency	—	175 🔴	213 🔴	402 🔴	30

310f227

Fri, 17 Jul 2026 19:14:49 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	stream	—	1699 🔴	1733 🔴	3652 🔴	30
TTFS	hook + stream	—	1943 🔴	2031 🔴	3686 🔴	30
STSO	1020 steps (1-20)	—	356 🔴	398 🔴	470 🔴	19
STSO	1020 steps (101-120)	—	308 🔴	405 🔴	555 🔴	19
STSO	1020 steps (1001-1020)	—	764 🔴	773 🔴	808 🔴	19
WO	stream	—	1699	1733	3652	30
WO	hook + stream	—	1943	2031	3686	30
SL	stream	—	5806 🔴	5933 🔴	6050 🔴	30
SL	hook + stream	—	5648 🔴	5729 🔴	6639 🔴	30

330a548

Fri, 17 Jul 2026 16:29:55 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	stream	—	1721 🔴	1783 🔴	1905 🔴	30
TTFS	hook + stream	—	2064 🔴	2121 🔴	2384 🔴	30
STSO	1020 steps (1-20)	—	333 🔴	436 🔴	521 🔴	19
STSO	1020 steps (101-120)	—	491 🔴	581 🔴	616 🔴	19
STSO	1020 steps (1001-1020)	—	938 🔴	999 🔴	1100 🔴	19
WO	stream	—	1721	1783	1905	30
WO	hook + stream	—	2064	2121	2384	30
SL	stream	—	5877 🔴	6059 🔴	6309 🔴	30
SL	hook + stream	—	5761 🔴	5825 🔴	7096 🔴	30

_{Best/P75/P90/P99 deltas compare against the most recent benchmark run on main at the time of this run. 🔻 flags a delta worse than +15%, 💚 one better than −15%.}

_{Metrics — TTFS: time to first step body (in-deployment start() → first step body, deployment clocks) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · SL: stream latency (in-deployment write → read propagation, readAt - writtenAt)}

_{Scenarios — step: one trivial no-op step, no stream; no hooks, so the run stays in turbo mode (in-process fast path) · stream: one streaming step; no hooks, so the run stays in turbo mode (in-process fast path) · hook + stream: registers a hook before one step, which exits turbo mode (dispatch path) · 1020 steps: 1020 trivial sequential steps; STSO is measured between consecutive steps in the given step ranges, and WO is the whole-run overhead outside step bodies · stream latency: parallel reader/writer steps on a dedicated stream; SL is the in-deployment write->read propagation (readAt - writtenAt)}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600 · SL 50/60/125 · STSO (1-20) 20/30/60 · STSO (101-120) 30/45/90 · STSO (1001-1020) 40/60/120}

_{All metrics are measured from deployment-side timestamps only. Runs are triggered by an in-deployment route that stamps the anchor (clientStart) right before start(), so the CI runner’s request and its path through api.vercel.com sit outside every measured window. TTFS = in-deployment start() → first step body (turbo uses the in-process fast path, non-turbo the dispatch path), and includes the VQS dispatch hop plus any /flow cold start. STSO/WO are measured between step bodies on the deployment. SL is measured inside the workflow (parallel reader/writer steps), so it no longer includes the api.vercel.com read path.}

_{Cold starts are kept in the numbers on purpose — they are part of real bursty-workload latency. The workbench deployment cold-starts the /flow invocation for a large fraction of runs, inflating P75+; the Best column shows the fastest (warm-start) sample for comparison.}

[github-actions]

🧪 E2E Test Results

✅ All tests passed

Summary

	Passed	Failed	Skipped	Total
✅ ▲ Vercel Production	1455	0	239	1694
✅ 💻 Local Development	1621	0	227	1848
✅ 📦 Local Production	1621	0	227	1848
✅ 🐘 Local Postgres	1621	0	227	1848
✅ 🪟 Windows	154	0	0	154
✅ 📋 Other	1020	0	212	1232
✅ vercel-multi-region	27	0	0	27
Total	7519	0	1132	8651

Details by Category

✅ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro	126	0	28
✅ example	126	0	28
✅ express	126	0	28
✅ fastify	126	0	28
✅ hono	126	0	28
✅ nextjs-turbopack	151	0	3
✅ nextjs-webpack	151	0	3
✅ nitro	126	0	28
✅ nuxt	126	0	28
✅ sveltekit	145	0	9
✅ vite	126	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable	128	0	26
✅ express-stable	128	0	26
✅ fastify-stable	128	0	26
✅ hono-stable	128	0	26
✅ nextjs-turbopack-canary	135	0	19
✅ nextjs-turbopack-stable	154	0	0
✅ nextjs-webpack-canary	135	0	19
✅ nextjs-webpack-stable	154	0	0
✅ nitro-stable	128	0	26
✅ nuxt-stable	128	0	26
✅ sveltekit-stable	147	0	7
✅ vite-stable	128	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable	128	0	26
✅ express-stable	128	0	26
✅ fastify-stable	128	0	26
✅ hono-stable	128	0	26
✅ nextjs-turbopack-canary	135	0	19
✅ nextjs-turbopack-stable	154	0	0
✅ nextjs-webpack-canary	135	0	19
✅ nextjs-webpack-stable	154	0	0
✅ nitro-stable	128	0	26
✅ nuxt-stable	128	0	26
✅ sveltekit-stable	147	0	7
✅ vite-stable	128	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable	128	0	26
✅ express-stable	128	0	26
✅ fastify-stable	128	0	26
✅ hono-stable	128	0	26
✅ nextjs-turbopack-canary	135	0	19
✅ nextjs-turbopack-stable	154	0	0
✅ nextjs-webpack-canary	135	0	19
✅ nextjs-webpack-stable	154	0	0
✅ nitro-stable	128	0	26
✅ nuxt-stable	128	0	26
✅ sveltekit-stable	147	0	7
✅ vite-stable	128	0	26

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack	154	0	0

✅ 📋 Other

App	Passed	Failed	Skipped
✅ e2e-local-dev-nest-stable	128	0	26
✅ e2e-local-dev-tanstack-start-	128	0	26
✅ e2e-local-postgres-nest-stable	128	0	26
✅ e2e-local-postgres-tanstack-start-	128	0	26
✅ e2e-local-prod-nest-stable	128	0	26
✅ e2e-local-prod-tanstack-start-	128	0	26
✅ e2e-vercel-prod-nest	126	0	28
✅ e2e-vercel-prod-tanstack-start	126	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

---

📋 View full workflow run

[shalabhc]

Made change to use server provided limit.
Refactored to raise a new max events exceeded error that gets caught and fails run via a prexisting catch.

[VaguelySerious]

Let's wait with merge until other PRs merge first

[vercel]

Additional Suggestion:

workbench/nest's vercel-build script invokes packages/nest/dist/cli.js without first compiling the @workflow/nest workspace dependency, so the file is missing and the build aborts with MODULE_NOT_FOUND.

[vercel]

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[github-actions]

Backport PR opened against stable: #3042. Merge conflicts were resolved by AI — please review carefully. (backport job run)