fix: retry backend connection failures and improve error logs by karthikscale3 · Pull Request #4179 · vercel/workflow

karthikscale3 · 2026-09-15T18:41:48Z

What changed

Retry backend connection and stream failures using existing policies, and replace unhealthy HTTP/2 event connections. Invalid backend URLs and unsupported headers fail immediately.
Include underlying error causes in failed-run logs and document recovery behavior.

Why

Network failures could fail workflows as user errors, with only an unhelpful fetch failed message.

Verification

Core and world-vercel builds and unit tests pass. Regression coverage includes request validation, cancellation, interrupted event-write retries, cause-chain logs, and connection-pool replacement.

Docs Preview

Backend connection failures

…port failure `makeRequest` and `instrumentedFetch` only wrapped a `fetch` rejection as a retryable `TRANSPORT` / `STREAM_ERROR` when `getTransientTransportCode` found a code from a fixed allowlist on the error or its `cause` chain. Anything else was rethrown raw, and a raw `TypeError: fetch failed` is indistinguishable from a user throw by the time it reaches `classifyRunError`: the run failed as `USER_ERROR`, attributing a backend outage to customer code, and `isRetryableWorldError` never redelivered the queue message. The allowlist can only ever name failures someone has already seen, and the ones it misses are ordinary: h2 session errors (`ERR_HTTP2_GOAWAY_SESSION` — the shared events pool negotiates h2), TLS handshake failures, `ENETUNREACH`, and the `AggregateError` a happy-eyeballs connect raises, which hangs its codes off `errors[]` where a `cause` walk cannot see them. A rejection from `fetch` / `nodeHttpFetch` means no response was produced at all, so `describeTransportFailure` inverts the default: everything is a transport failure unless it is a request-construction fault (`ERR_INVALID_URL` and friends), which is permanent and must keep failing fast rather than burning the run's delivery budget re-forming the same broken request. Known codes still name themselves in the message, so existing failures report exactly what they reported before, including the `UND_ERR_CONNECT_TIMEOUT` retry branch. Agent selection and `Request` construction move out of the try blocks so the catch only ever sees the request on the wire. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Co-Authored-By: Karthik Kalyan <105607645+karthikscale3@users.noreply.github.com>

… log The run-failure log prints `errorMessage` and the source-map-remapped `errorStack`, and neither says anything when the terminal error is a wrapper. `TypeError: fetch failed` is the canonical case: undici's wrapper carries that fixed message by design and a stack of pure `node:internal/` frames, all of which the formatter's framework-frame trim drops. The socket, DNS or TLS failure that actually happened lives one or two `cause` hops down, and nothing in the log pipeline read it. Same for the world layer's own wrapping, where the wrapper names the request and the cause names what went wrong with it. `formatErrorCauseChain` summarizes the chain, one `Name: message (CODE)` line per link, skipping the value itself (the log already prints that) and summarizing an `AggregateError`'s collected attempts, which is where a happy-eyeballs connect reports every address it tried. `composeLogLine` renders it as a `cause` row under the message it explains, and skips it when the stack body already spells the chain out. The field is undefined when there is no cause, so an ordinary user throw logs exactly as before. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Co-Authored-By: Karthik Kalyan <105607645+karthikscale3@users.noreply.github.com>

vercel · 2026-09-15T18:41:53Z

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

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
example-workflow	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
workbench-astro-workflow	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
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workbench-fastify-workflow	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
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workbench-nestjs-workflow	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
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workbench-python-workflow	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
workbench-vite-workflow	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
workflow-docs	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
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workflow-tarballs	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC
workflow-web	Ready	Preview, v0	Sep 15, 2026 10:34pm UTC

changeset-bot · 2026-09-15T18:41:57Z

🦋 Changeset detected

Latest commit: 39cb5e7

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

This PR includes changesets to release 17 packages

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

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

github-actions · 2026-09-15T18:42:10Z

📊 Workflow Benchmarks

commit 39cb5e7 · Tue, 15 Sep 2026 22:57:13 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	327 (-68%) 💚	1729 🔴 (+19%) 🔻	1748 🔴 (+3.1%)	1888 🔴 (-2.3%)	30
TTFS	stream	201 (-85%) 💚	1788 🔴 (+27%) 🔻	1811 🔴 (+25%) 🔻	1866 🔴 (+25%) 🔻	30
TTFS	hook + stream	2052 (+23%) 🔻	2200 🔴 (+20%) 🔻	2237 🔴 (+18%) 🔻	2361 🔴 (+17%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	460 (+9.3%)	1040 (+50%) 🔻	2195 (+121%) 🔻	2575 (+50%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1365 (-21%) 💚	3115 (-31%) 💚	3466 (-35%) 💚	9954 (+38%) 🔻	10
STSO	1020 steps (inline)	101 (-23%) 💚	150 (-7.4%)	166 (-7.8%)	264 (+11%)	1019
WO	1020 steps	150111 (-8.3%)	150111 (-8.3%)	150111 (-8.3%)	150111 (-8.3%)	1
CRTT	first chunk (pooled)	72 (+14%)	121 (+29%) 🔻	651 (+520%) 🔻	4053 (+1830%) 🔻	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	106 (+29%)	225 (+10%)	3639 (+1223%)	4020 (+866%)	177 (-3%)	10
size sweep (100/s, 160B-12KB)	108 (+20%)	216 (±0%)	475 (+33%)	902 (+26%)	146 (-32%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	91 (+18%)	169 (-21%)	203 (-33%)	395 (-33%)	222 (-46%)	3
replay eve-gpt-5.6-sol-2000t (1x)	97 (+24%)	168 (+1%)	200 (-16%)	498 (-6%)	409 (+18%)	2
replay eve-gpt-5.6-sol-2000t (2x)	80 (-14%)	264 (-7%)	401 (-30%)	750 (-20%)	595 (+15%)	3

📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 162443ms → this run 149939ms (Δ -12504ms, -8%)

100-150 ms  ██████████░░░░░░░░░░░░░┃  main 325  this 758  +433
150-200 ms  ██████┃██████████████     main 658  this 226  -432
200-250 ms  ┃                         main  29  this  20    -9
250-300 ms  ┃                         main   3  this  10    +7
300-350 ms  ┃                         main   1  this   2    +1
350-400 ms  ┃                         main   3  this   3    +0

📈 CRTT drill-down vs main (RTT distributions & profiles)

variant  RTT 1ms→5s+              avg         p50            p90           p99     n
control  ······▁█▃·▁▂·  641.1 (+325%)  155 (+18%)  3639 (+1223%)  4020 (+866%)  3000
sweep    ······▁█▃▁···   189.9 (+15%)  157 (+16%)     475 (+33%)    902 (+26%)  3000
gw 1x    ·····▁▂█▁▁···   142.2 (-14%)   135 (-2%)     203 (-33%)    395 (-33%)  5295
eve 1x   ······▂█▂▁···      146 (+3%)  135 (+11%)     200 (-16%)     498 (-6%)  5186
eve 2x   ·····▁▁█▅▁···    206.4 (-7%)  194 (+14%)     401 (-30%)    750 (-20%)  7779

RTT over stream progress (avg per tenth of stream, bars scaled min→max):

control  █▇▇▆▅▄▃▂▂▁  380–905ms
sweep    █▇▅▂▁▁▅█▇▄  151–224ms
gw 1x    ▁▃▅▃▅█▄▆▅█  126–156ms
eve 1x   █▁▂▂▁▁▃▇▃▂  134–177ms
eve 2x   ▄▁▄▂▂▂▃█▂▃  160–324ms

RTT by chunk size (avg per log size bin, ~160B → ~12KB serialized, bars scaled min→max):

sweep  ▇█▆▁▆█▇  188–191ms

Delivery jitter over stream progress (avg positive CDV per tenth of stream, bars scaled min→max):

control  ▁▅▃▂▁▇▄▃█▁  48–68ms
sweep    ▄▁▃▂▁▃▄█▂▁  59–92ms
gw 1x    ▄▄▄▁▄█▄▄▃▆  40–56ms
eve 1x   █▂▂▂▁▇▅▅▃▃  26–33ms
eve 2x   █▄▆▁▄▄▃▂▃▄  22–40ms

ℹ️ Metric definitions & methodology

_{Streams: first-chunk RTT (the stream-open path, before any buffering/backpressure), CRTT percentiles, and worst delivery stall (CDV max). Cells are medians across iterations; per-run values in the artifacts. No 🔴/🟢 marks until targets attach.}

_{The collapsed STSO distribution section above buckets every step gap, split inline (same warm process — pure framework overhead) vs queue-hop (fresh process — dispatch, reinit, replay). █ = main, ┃ = this run, ░ = fill.}

_{The collapsed CRTT drill-down: per-variant RTT histograms (fixed log bins, · = empty) and mean RTT/positive-CDV profile lines over stream progress and chunk size. Histograms, avgs, and profiles merge exactly across runs; p50–p99 are percentile-of-percentiles. Per-index rows live in the artifacts.}

_{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) · Fan-out TTFS: fan-out time to first step (in-deployment start() → first of the parallel step bodies to complete) · Fan-out TTLS: fan-out time to last step (in-deployment start() → last of the parallel step bodies to complete, i.e. when the Promise.all resolves) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · CRTT: chunk round-trip time (per-chunk write → read latency, one clock domain: deployment → stream backend → same deployment) · CDV: chunk delay variation / delivery jitter (inter-arrival gap minus inter-write gap per seq-adjacent pair; skew-free; the row is each run's MAX positive value, so one stall moves it)}

_{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 · Promise.all(100 steps): 100 trivial no-op steps started together in a single Promise.all; Fan-out TTFS is the first of them to complete and Fan-out TTLS the last, both from the in-deployment clientStart, so their gap is the spread the runtime adds across the fan-out · paced control (100/s, 60B): the control: 300 tiny (~60B) deltas metronome-paced at 100/s — zero workload structure, so it reads the transport floor and flush cadence, and disambiguates transport-wide vs workload-specific when a replay row moves · size sweep (100/s, 160B-12KB): same pacing as the control with deltas padded in rotation across seven log-spaced sizes (~160B–12KB) — rotation decouples size from stream position, so it isolates whether chunk size causes latency · replay gateway-gpt-5.4-nano-2000t (1x): raw provider SSE cadence captured at the AI gateway boundary (gpt-5.4-nano, the most popular gateway model; per-token deltas p50 208B = the modal production chunk size), replayed exactly as measured — the typical customer's workload; its CDV is the typical customer's real delivery jitter · replay eve-gpt-5.6-sol-2000t (1x): a captured eve turn (gpt-5.6-sol, the most-used demanding eve model; ~2000 output tokens = production p50 turn length) replayed exactly as measured — eve's envelope protocol re-ships the cumulative message so sizes ramp 142B→13KB; the demanding outlier tenant's reality · replay eve-gpt-5.6-sol-2000t (2x): the same eve capture at 2x — the headroom/stress row; real fast-tier models emit the same chunk sizes at proportionally higher rate, so time compression is a faithful speed model · first chunk (pooled): every run's seq-0 RTT pooled across all stream scenarios — the first chunk precedes any workload differentiation, so pooling samples one shared stream-open path with exact percentiles}

_{Replay cadences (semantic sha256) — eve-gpt-5.6-sol-2000t eaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t 6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600}

_{All timestamps are deployment-side; runs are triggered in-deployment, so the CI runner and api.vercel.com sit outside every measured window. TTFS = start() → first step body (includes dispatch + any cold start); Fan-out TTFS/TTLS = first/last step completion of one Promise.all from the same anchor (the gap is the runtime’s fan-out spread); STSO/WO between step bodies; CRTT inside the workflow (excludes the api.vercel.com read path).}

_{Cold starts stay in the numbers (real bursty-workload latency, inflates P75+); Best is the warm floor.}

github-actions · 2026-09-15T18:42:10Z

🧪 E2E Test Results

✅ All tests passed

⚠️ Flaky E2E Tests (passed on retry)

These tests failed at least once and passed on a retry. A recurring entry here is a real race worth investigating.

sleepWinsRaceWorkflow (tanstack-start · local-dev / local / quickjs)
sleepWinsRaceWorkflow (vite · local-dev / local / quickjs / stable)

🛠 Infra Events (absorbed by the harness)

Platform anomalies the e2e harness detected and worked around (e.g. a run the queue never picked up, replaced by a fresh run). Clustered timestamps indicate a backend blip; a steady drip indicates a platform issue worth escalating.

cold-start-warmup · suite warmup (astro) · at 22:38:31Z · abandoned wrun_01M2KKH2GXQ50E13N6P7XH0478
cold-start-warmup · suite warmup (tanstack-start) · at 22:38:36Z · abandoned wrun_01M2KKGVSNR40B6DMCN2M22ABZ
run-pickup-stall · regular Error retries until success (vite) · at 22:40:38Z · abandoned wrun_01M2KKMZMRQP45W2BM7DYNF1GG

E2E Test Summary

Summary

	Passed	Skipped	Total
✅ ▲ Vercel Production	3662	685	4347
✅ 💻 Local Development	3998	510	4508
✅ 📦 Local Production	3998	510	4508
✅ 🐘 Local Postgres	3998	510	4508
✅ 🪟 Windows	320	2	322
✅ 🌐 Cross-language Conformance	68	74	142
✅ vercel-http-transport	823	143	966
✅ vercel-multi-region	27	0	27
✅ vercel-ws-transport	557	87	644
Total	17451	2521	19972

Details by Category

✅ ▲ Vercel Production

App	Passed	Skipped
✅ astro-node	133	28
✅ astro-quickjs	133	28
✅ example-node	133	28
✅ example-quickjs	133	28
✅ express-node	133	28
✅ express-quickjs	133	28
✅ fastify-node	133	28
✅ fastify-quickjs	133	28
✅ hono-node	133	28
✅ hono-quickjs	133	28
✅ nest-node	133	28
✅ nest-quickjs	133	28
✅ nextjs-turbopack-node	158	3
✅ nextjs-turbopack-quickjs	158	3
✅ nextjs-webpack-node	158	3
✅ nextjs-webpack-quickjs	158	3
✅ nitro-node	133	28
✅ nitro-quickjs	133	28
✅ nuxt-node	133	28
✅ nuxt-quickjs	133	28
✅ python-node	66	95
✅ sveltekit-node	152	9
✅ sveltekit-quickjs	152	9
✅ tanstack-start-node	133	28
✅ tanstack-start-quickjs	133	28
✅ vite-node	133	28
✅ vite-quickjs	133	28

✅ 💻 Local Development

App	Passed	Skipped
✅ astro-stable-node	134	27
✅ astro-stable-quickjs	134	27
✅ express-stable-node	134	27
✅ express-stable-quickjs	134	27
✅ fastify-stable-node	134	27
✅ fastify-stable-quickjs	134	27
✅ hono-stable-node	134	27
✅ hono-stable-quickjs	134	27
✅ nest-stable-node	134	27
✅ nest-stable-quickjs	134	27
✅ nextjs-turbopack-canary-node	160	1
✅ nextjs-turbopack-canary-quickjs	160	1
✅ nextjs-turbopack-stable-node	160	1
✅ nextjs-turbopack-stable-quickjs	160	1
✅ nextjs-webpack-canary-node	160	1
✅ nextjs-webpack-canary-quickjs	160	1
✅ nextjs-webpack-stable-node	160	1
✅ nextjs-webpack-stable-quickjs	160	1
✅ nitro-stable-node	134	27
✅ nitro-stable-quickjs	134	27
✅ nuxt-stable-node	134	27
✅ nuxt-stable-quickjs	134	27
✅ sveltekit-stable-node	153	8
✅ sveltekit-stable-quickjs	153	8
✅ tanstack-start-node	134	27
✅ tanstack-start-quickjs	134	27
✅ vite-stable-node	134	27
✅ vite-stable-quickjs	134	27

✅ 📦 Local Production

App	Passed	Skipped
✅ astro-stable-node	134	27
✅ astro-stable-quickjs	134	27
✅ express-stable-node	134	27
✅ express-stable-quickjs	134	27
✅ fastify-stable-node	134	27
✅ fastify-stable-quickjs	134	27
✅ hono-stable-node	134	27
✅ hono-stable-quickjs	134	27
✅ nest-stable-node	134	27
✅ nest-stable-quickjs	134	27
✅ nextjs-turbopack-canary-node	160	1
✅ nextjs-turbopack-canary-quickjs	160	1
✅ nextjs-turbopack-stable-node	160	1
✅ nextjs-turbopack-stable-quickjs	160	1
✅ nextjs-webpack-canary-node	160	1
✅ nextjs-webpack-canary-quickjs	160	1
✅ nextjs-webpack-stable-node	160	1
✅ nextjs-webpack-stable-quickjs	160	1
✅ nitro-stable-node	134	27
✅ nitro-stable-quickjs	134	27
✅ nuxt-stable-node	134	27
✅ nuxt-stable-quickjs	134	27
✅ sveltekit-stable-node	153	8
✅ sveltekit-stable-quickjs	153	8
✅ tanstack-start-node	134	27
✅ tanstack-start-quickjs	134	27
✅ vite-stable-node	134	27
✅ vite-stable-quickjs	134	27

✅ 🐘 Local Postgres

App	Passed	Skipped
✅ astro-stable-node	134	27
✅ astro-stable-quickjs	134	27
✅ express-stable-node	134	27
✅ express-stable-quickjs	134	27
✅ fastify-stable-node	134	27
✅ fastify-stable-quickjs	134	27
✅ hono-stable-node	134	27
✅ hono-stable-quickjs	134	27
✅ nest-stable-node	134	27
✅ nest-stable-quickjs	134	27
✅ nextjs-turbopack-canary-node	160	1
✅ nextjs-turbopack-canary-quickjs	160	1
✅ nextjs-turbopack-stable-node	160	1
✅ nextjs-turbopack-stable-quickjs	160	1
✅ nextjs-webpack-canary-node	160	1
✅ nextjs-webpack-canary-quickjs	160	1
✅ nextjs-webpack-stable-node	160	1
✅ nextjs-webpack-stable-quickjs	160	1
✅ nitro-stable-node	134	27
✅ nitro-stable-quickjs	134	27
✅ nuxt-stable-node	134	27
✅ nuxt-stable-quickjs	134	27
✅ sveltekit-stable-node	153	8
✅ sveltekit-stable-quickjs	153	8
✅ tanstack-start-node	134	27
✅ tanstack-start-quickjs	134	27
✅ vite-stable-node	134	27
✅ vite-stable-quickjs	134	27

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	160	0	1
✅ nextjs-turbopack-quickjs	160	0	1

✅ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
✅ python	68	0	74

✅ vercel-http-transport

App	Passed	Skipped
✅ example	133	28
✅ express	133	28
✅ hono	133	28
✅ nextjs-turbopack	158	3
✅ nitro	133	28
✅ vite	133	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Skipped
✅ example	133	28
✅ express	133	28
✅ nextjs-turbopack	158	3
✅ vite	133	28

📋 View full workflow run

github-actions · 2026-09-15T18:45:32Z

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 41 total

fence=per-spec

scenario	outcome	events	virt	replay
✅ `smoke-no-steps`	completed	3	0ms	ok
✅ `smoke-one-step`	completed	6	0ms	ok
✅ `hook-at-step-started`	completed	12	0ms	ok
✅ `hook-at-step-completed`	completed	12	0ms	ok
✅ `hook-at-hook-created`	completed	12	0ms	ok
✅ `deadline-hook-wins`	completed	7	1.0h	ok
✅ `deadline-expires`	completed	7	1.0h	ok
✅ `long-sleep`	completed	11	30.0d	ok
✅ `hook-never-arrives`	stalled	3	0ms	skipped
✅ `step-retries-twice`	completed	10	2.0s	ok
✅ `parallel-steps`	completed	9	0ms	ok
✅ `hook-on-execution-state`	completed	12	0ms	ok
✅ `peek-hook-before-branch`	completed	12	0ms	ok
✅ `peek-hook-after-branch`	completed	12	0ms	ok
✅ `peek-hook-at-registration`	completed	12	0ms	ok
✅ `race-hook-before-probe`	completed	12	0ms	ok
✅ `race-hook-after-probe`	completed	12	0ms	ok
✅ `race-duplicate-delivery`	completed	13	0ms	ok
✅ `attr-hook-before-step`	completed	11	0ms	ok
✅ `attr-hook-after-step`	completed	11	0ms	ok
✅ `attr-from-step-body`	completed	13	0ms	ok
✅ `fork-hook-after-timeout`	completed	14	1.0m	ok
✅ `fork-hook-before-timeout`	completed	14	1.0m	ok
✅ `count-hook-after-timeout`	completed	17	1.0m	ok
✅ `count-hook-before-timeout`	completed	20	1.0m	ok
✅ `stale-read-step-count-fork`	completed	20	1.0m	ok
✅ `stale-read-equal-step-counts`	completed	14	1.0m	ok
✅ `step-vs-step-fork`	completed	12	0ms	ok
✅ `step-vs-step-fork-fenced`	completed	12	0ms	ok
✅ `fence-catches-benign-direction`	completed	12	5ms	ok
✅ `in-flight-before-decision`	completed	17	1.0m	ok
❌ `in-flight-before-decision-counted`	completed	17	1.0m	ok
✅ `in-flight-after-decision`	completed	19	2.0m	ok
✅ `stale-read-step-count-fork-fenced`	completed	20	1.0m	ok
✅ `fork-hook-wins`	completed	13	1.0m	ok
✅ `fork-timeout-wins`	completed	13	1.0m	ok
✅ `unclaimed-payload-under-fork`	completed	17	1.0m	ok
✅ `claimed-payload-under-fork`	completed	17	1.0m	ok
✅ `writers-independent-step-bodies`	completed	12	0ms	ok
✅ `writers-scripted-tempo`	completed	12	0ms	ok
✅ `cancel-mid-step`	cancelled	7	0ms	skipped

Full trace: world-sim.txt

github-actions · 2026-09-15T18:46:39Z

Framework	Flow route	Step reg.	Framework output
hono	250.7 KiB (±0)	93.0 KiB (±0)	1.89 MiB (+2.4 KiB)
nextjs-turbopack	257.2 KiB (±0)	426 B (±0)	898.5 KiB (+678 B)

About these numbers

Sizes are gzip; parentheses show the change against main.
Flow route and Step reg. gate this job, on raw bytes rather than the gzip shown, at max(2%, 50.0 KiB). Framework output is informational.

39cb5e7 · run

VaguelySerious

AI review: blocking issues found

VaguelySerious · 2026-09-15T19:45:05Z

AI Review: Blocking

packages/world-vercel/src/events-v4.ts:167 still uses the old allowlist once response headers have arrived. An unrecognized socket or HTTP/2 failure while reading the event body is therefore propagated raw and can again be classified as a user error, even though it is the same backend connection failure this change is intended to retry. Please apply the transport classification to response-stream read failures as well and add coverage for a stream interrupted after headers.

VaguelySerious · 2026-09-15T19:45:06Z

AI Review: Note

packages/world-vercel/src/http-client.ts:648 retains a narrower recycler allowlist than the newly retryable failure set. In particular, an unknown HTTP/2 session error can now be retried while the warm process continues using the same unhealthy dispatcher. Please add coverage tying the new classification to recycler behavior, or document why the dispatcher always evicts these sessions itself.

The retry semantics and failed-run cause output are user-visible, but this PR only updates the changeset. Please document the behavior in the user-facing docs.

VaguelySerious

AI review: blocking issues found

VaguelySerious · 2026-09-15T20:02:24Z

AI Review: Blocking

Re-review at 32c8544 confirms that packages/world-vercel/src/events-v4.ts:167 is still blocking approval. I added a disposable regression where createWorkflowRunEventsBatchV4 receives response headers and then its body fails with ERR_HTTP2_GOAWAY_SESSION. The call rejects with the raw Error: The session has been destroyed rather than StreamError, so withEventPostRetry does not recognize the backend failure as retryable. The blocked-port finding is fixed, but the post-header V4 path still needs to use the open-ended transport classification and cover this batch consumer.

VaguelySerious · 2026-09-15T20:32:23Z

AI Review: Note

Addressed the post-header V4 transport blocker in 954bc61. Response-body read failures now use the same open-ended transport classification as pre-header failures, so an unrecognized HTTP/2 session failure is surfaced as StreamError and reaches the existing event retry policy. Added regression coverage through createWorkflowRunEventsBatchV4 for headers followed by ERR_HTTP2_GOAWAY_SESSION.

Validation: @workflow/world-vercel build, all 729 package tests, focused 60-test V4 suite, typecheck, formatting, and git diff --check pass.

VaguelySerious

AI review: blocking issues found

karthikscale3

Addressed the remaining connection-pool and documentation review notes in 2373ca4. Both package builds pass; 3,195 core/world-vercel tests pass (3 expected failures, 1 skipped).

karthikscale3 · 2026-09-15T22:19:22Z

+  'ERR_HTTP2_GOAWAY_SESSION',
+  'ERR_HTTP2_INVALID_SESSION',
+  'ERR_HTTP2_SESSION_ERROR',
+  'ERR_HTTP2_STREAM_ERROR',


Addressed the recycler review note in 2373ca4. Added GOAWAY, invalid-session, session-error, and stream-error codes to pool recycling. Pre- and post-header regressions now verify that GOAWAY failures remain StreamError, preserve their cause, and replace the shared pool after three failures. DNS/TLS/connect failures, request validation, and caller cancellation remain excluded from recycling.

karthikscale3 · 2026-09-15T22:19:23Z

+
+A connection failure does not prove that the backend rejected a write: it may have accepted it before the response was lost. Continue to make step side effects [idempotent](/docs/foundations/idempotency).
+
+Failed-run logs include the underlying error causes and their codes, exposing socket, DNS, or TLS errors behind messages such as `TypeError: fetch failed`. If a cause cannot be read, the log includes `[unavailable cause]` and the run can still be recorded as failed.


Addressed the documentation review note in 2373ca4. Added user-facing docs for backend retries, HTTP/2 pool recovery, invalid URLs, write-outcome uncertainty, and cause-chain logs. Updated both package READMEs and the existing single changeset; the PR description links to the docs preview.

karthikscale3

Fixed both follow-up P2 findings in 39cb5e7. Both package builds and 3,212 core/world-vercel tests pass (3 expected failures, 1 skipped).

karthikscale3 · 2026-09-15T22:30:31Z

+          'ABORT_ERR',
+          'UND_ERR_ABORTED',
+          'ERR_HTTP2_STREAM_CANCEL',
+        ].includes(marker)


Fixed the V4 event-write retry regression. The helper now explicitly recognizes StreamError (the WorkflowWorldError.is() guard excludes subclasses) and retries eligible stream failures while excluding caller cancellations. Regression tests exercise interrupted step_completed batch responses through the actual event-write wrapper: GOAWAY and uncoded failures retry and observe the original write’s 409; cancellation sends no second request.

karthikscale3 · 2026-09-15T22:30:31Z

+  // Undici validates request options and headers during dispatch, after
+  // Fetch has constructed the Request (e.g. unsupported Expect headers).
+  'UND_ERR_INVALID_ARG',
+  'UND_ERR_NOT_SUPPORTED',


Fixed permanent Undici request failures becoming retryable. UND_ERR_NOT_SUPPORTED and UND_ERR_INVALID_ARG now preserve the original rejection. Real Fetch regressions cover Expect: 100-continue and invalid Connection headers in both transport-error modes, plus the supported V4 backend-header configuration. Updated the existing changeset and docs.

github-actions · 2026-09-16T00:48:58Z

Backport PR opened against stable: #4190. Merge conflicts were resolved by AI — please review carefully. (backport job run)

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chore: combine transport and run failure changesets

9c17f60

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karthikscale3 changed the title ~~fix: classify response-less fetch failures as retryable transport errors, and surface the cause in the run-failure log~~ fix: retry backend connection failures and improve error logs Sep 15, 2026

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VaguelySerious reviewed Sep 15, 2026

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Comment thread packages/world-vercel/src/http-core.ts

fix: preserve Fetch blocked-port errors without retrying

32c8544

VaguelySerious reviewed Sep 15, 2026

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fix: classify v4 response stream failures

954bc61

VaguelySerious reviewed Sep 15, 2026

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Comment thread packages/world-vercel/src/http-core.ts

VaguelySerious and others added 2 commits September 15, 2026 14:05

fix: reject credential-bearing backend URLs

b6aeb23

fix: recycle failed HTTP/2 sessions and document recovery

2373ca4

karthikscale3 commented Sep 15, 2026

View reviewed changes

karthikscale3 and others added 2 commits September 15, 2026 15:21

Merge branch 'main' into fetch-failure-classification

13df42b

fix: preserve event-write retries and reject invalid request headers

39cb5e7

karthikscale3 commented Sep 15, 2026

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VaguelySerious approved these changes Sep 16, 2026

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github-actions Bot mentioned this pull request Sep 16, 2026

Version Packages (beta) #4170

Merged

This was referenced Sep 16, 2026

Backport #4179: fix: retry backend connection failures and improve error logs #4190

Merged

Version Packages #4182

Merged


		A connection failure does not prove that the backend rejected a write: it may have accepted it before the response was lost. Continue to make step side effects [idempotent](/docs/foundations/idempotency).

		Failed-run logs include the underlying error causes and their codes, exposing socket, DNS, or TLS errors behind messages such as `TypeError: fetch failed`. If a cause cannot be read, the log includes `[unavailable cause]` and the run can still be recorded as failed.

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