test(next): cover HMR rebuild convergence by NathanColosimo · Pull Request #3471 · vercel/workflow

NathanColosimo · 2026-08-11T20:18:46Z

Summary

make expected hot, full, and skipped rebuild counts explicit
verify body-only edits stay hot while import, add, and remove changes rediscover workflows
verify editing an imported dependency updates workflow execution on stable and canary Next.js
test Next.js 16.3.1 and 16.3.1-canary.21 across Turbopack, webpack, Node.js, and QuickJS

Testing

pnpm --filter @workflow/next build
pnpm --filter @workflow/next test
focused local Next.js 16.3.1-canary.21 HMR scenario with Turbopack and webpack
GitHub Actions Next.js local-development matrix

Stack

fix(next): converge workflow HMR rebuilds #3333: rebuild convergence and unit coverage
fix(next): watch before initial build #3470: close the startup observation gap
This PR: stable/canary end-to-end HMR coverage

_{Stack created with GitHub Stacks CLI • Give Feedback 💬}

changeset-bot · 2026-08-11T20:18:49Z

🦋 Changeset detected

Latest commit: da9995c

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

This PR includes changesets to release 0 packages

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

github-actions · 2026-08-11T20:19:02Z

🧪 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 / node)
stepWinsRaceWorkflow (vite · local-dev / local / node / 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 22:49:32Z · abandoned wrun_01M2H1RAC17ZNRJTTXYA927CP0
cold-start-warmup · suite warmup (tanstack-start) · at 22:49:38Z · abandoned wrun_01M2H1RGMB682N0MFR14H529ET
run-pickup-stall · hookWorkflow (nuxt) · at 22:50:05Z · abandoned wrun_01M2H1SJEZEVAGHWBYZ4FFKXR0

E2E Test Summary

Summary

	Passed	Skipped	Total
✅ ▲ Vercel Production	3662	685	4347
✅ 💻 Local Development	2718	502	3220
✅ 📦 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	16171	2513	18684

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
✅ 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

vercel · 2026-08-11T20:19:03Z

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

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
example-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workbench-astro-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workbench-express-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workbench-fastify-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workbench-hono-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workbench-nestjs-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workbench-nitro-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workbench-nuxt-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workbench-python-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workbench-vite-workflow	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workflow-docs	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workflow-swc-playground	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workflow-tarballs	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC
workflow-web	Ready	Preview, v0	Sep 14, 2026 10:49pm UTC

github-actions · 2026-08-11T20:19:07Z

📊 Workflow Benchmarks

commit da9995c · Mon, 14 Sep 2026 23:03:56 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1565 (+18%) 🔻	1657 🔴 (+15%)	1832 🔴 (+25%) 🔻	2114 🔴 (+31%) 🔻	30
TTFS	stream	1547 (+706%) 🔻	1645 🔴 (+15%) 🔻	1665 🔴 (+14%)	1681 🔴 (+12%)	30
TTFS	hook + stream	549 (-4.4%)	2044 🔴 (+11%)	2125 🔴 (+8.4%)	6287 🔴 (+173%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	468 (+3.3%)	684 (+1.2%)	704 (-62%) 💚	6658 (+259%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1583 (-5.7%)	3762 (+15%) 🔻	4922 (+13%)	10307 (+30%) 🔻	10
STSO	1020 steps (inline)	137 (+8.7%)	162 (+1.9%)	178 (-1.1%)	261 (+23%) 🔻	1019
WO	1020 steps	163058 (+2.6%)	163058 (+2.6%)	163058 (+2.6%)	163058 (+2.6%)	1
CRTT	first chunk (pooled)	60 (-34%) 💚	86 (-42%) 💚	96 (-53%) 💚	161 (-27%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	73 (-49%)	169 (-58%)	329 (-44%)	676 (-18%)	165 (-42%)	10
size sweep (100/s, 160B-12KB)	81 (-39%)	144 (-64%)	221 (-58%)	353 (-62%)	128 (-51%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	89 (-21%)	160 (-40%)	265 (-33%)	644 (+8%)	324 (-20%)	3
replay eve-gpt-5.6-sol-2000t (1x)	81.5 (-50%)	160 (-38%)	247 (-27%)	567 (-25%)	359 (-48%)	2
replay eve-gpt-5.6-sol-2000t (2x)	72 (-43%)	188 (-59%)	265 (-59%)	465 (-62%)	254 (-41%)	3

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

1020 steps (inline)

Cumulative STSO time: main 158739ms → this run 162934ms (Δ +4195ms, +3%)

100-150 ms  ███████┃█████████         main 512  this 243  -269
150-200 ms  ████████████████░░░░░░░┃  main 477  this 735  +258
200-250 ms  ┃                         main  26  this  29    +3
250-300 ms  ┃                         main   2  this   9    +7
300-350 ms  ┃                         main   0  this   3    +3
400-450 ms  ┃                         main   2  this   0    -2

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

variant  RTT 1ms→5s+             avg         p50         p90         p99     n
control  ······▃█▂▁···  142.8 (-47%)  126 (-43%)  329 (-44%)  676 (-18%)  3000
sweep    ······▃█▁····  125.8 (-56%)  120 (-48%)  221 (-58%)  353 (-62%)  3000
gw 1x    ·····▁▄█▂▁···  138.9 (-31%)  122 (-31%)  265 (-33%)   644 (+8%)  5295
eve 1x   ·····▁▄█▂▁···  132.9 (-37%)  114 (-36%)  247 (-27%)  567 (-25%)  5186
eve 2x   ·····▁▂█▃▁···  159.2 (-51%)  145 (-54%)  265 (-59%)  465 (-62%)  7779

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

control  ▃▇▄▄█▄▃▅▃▁  114–178ms
sweep    █▂▂▆▂▂▄▅▁▁  116–146ms
gw 1x    █▄▂█▄▁▄▂▃▁  117–173ms
eve 1x   ▂▁▂▄▂▂▅▅█▂  108–183ms
eve 2x   ▃▂█▅▁▃▅█▇▁  125–197ms

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

sweep  ▆▅▄▄▁▃█  124–128ms

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

control  ▄▇▃█▇▃▅▄▃▁  33–53ms
sweep    ▁▁▆█▄▆▆█▄▃  46–64ms
gw 1x    █▃▁▃▄▂▄▂▃▂  35–58ms
eve 1x   ▃▂▁▄▃▁█▇▄▅  21–32ms
eve 2x   ██▅▄▅▃▄▁▄▅  21–31ms

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 · 2026-08-11T20:22:41Z

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 · 2026-08-26T07:55:42Z

Framework	Flow route	Step reg.	Framework output
hono	250.7 KiB (±0)	93.0 KiB (±0)	1.89 MiB (±0)
nextjs-turbopack	257.2 KiB (±0)	426 B (±0)	897.9 KiB (±0)

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.

da9995c · run

# Conflicts: # .github/workflows/tests.yml # packages/next/package.json # pnpm-lock.yaml # workbench/nextjs-turbopack/package.json # workbench/nextjs-webpack/package.json

VaguelySerious · 2026-09-14T23:40:32Z

AI Review: Blocking

The Local Dev lanes are red for a specific, reproducible reason, and it is worth deciding what it means before this lands.

8 of 8 Next dev lanes fail identically (turbopack + webpack × stable + canary × node + quickjs), all on the same assertion, freshly as of 22:53 today:

FAIL packages/core/e2e/dev.test.ts > should follow Next flow-route HMR rebuild rules for body-only changes
Timed out after 90000ms waiting for step HMR update to affect workflow execution.
Last error: Workflow run "wrun_..." failed: Step "step//./workflows/hmr-fuzz-serde//hmrFuzzSerdeStep"
failed after 3 retries: Class "HmrFuzzBox" not found. Make sure the class is registered with
registerSerializationClass.

Identical failure across all eight is not flakiness.

What changed. The test name predates this PR, but the assertion does not. This PR adds hmrFuzzSerdeStep(value: HmrFuzzBox) to the hmr-fuzz-serde fixture and has the workflow call await hmrFuzzSerdeStep(new HmrFuzzBox(workflowValue)). That makes a custom-serde class cross the step boundary as an argument for the first time in this suite, so the step has to deserialize it, which requires the class in the step bundle's registry. It isn't there.

Why I think this is a product gap rather than a bad fixture, with the caveat that I did not reproduce it locally:

The fixture uses the declarative convention (static classId plus the workflow-serialize / workflow-deserialize symbols), which is the same convention workbench/example/workflows/serde-models.ts uses.
Hybrid modules that define both serializers and steps do work in static builds: workbench/example/workflows/99_e2e.ts has 94 'use step' occurrences alongside 3 serializer classes and passes the Vercel Prod lanes.
The fixture's distinguishing property is that the class and the step live in the same file and that file is being rewritten by HMR. So the delta against the known-working cases is the dev rebuild path, not the convention.

If that is right, the registration gap is a bug in the dev builder for hybrid serde+step modules, and fixing it is out of scope for a PR whose job is test coverage. The stack under this one (#3333, #3470) does not address it. This is the same family of problem as #3639, which exists because hybrid serializer sources need special handling at bundle boundaries.

Recommended: triage the failure first. If it is a product bug, split it out and let this PR land the coverage that passes; if the fixture simply needs an explicit registerSerializationClass, that is a two-line change here.

Not blocking, for the record: the Unit Tests (windows-latest) failure is unrelated and is the known world-local hook-convergence flake (src/storage.test.ts > converges same-hook creation across separate storage instances to one event, expected 25 got 26). Windows unit passed on the two most recent main runs, so a re-run should clear it.

DCO is red for the org-membership reason explained on #3333, not for anything in this diff.

VaguelySerious

AI review: blocking issues found

VaguelySerious · 2026-09-16T01:28:48Z

+                value: `serde-body-${iteration}`,
+              }) satisfies ExpectedWorkflowResult,
            source: (iteration: number) => `export class HmrFuzzBox {
  static classId = 'HmrFuzzBox';


AI Review: Blocking

All 8 E2E Local Dev Tests lanes on this PR fail deterministically (run 34905603125, head da9995c5):

Step "step//./workflows/hmr-fuzz-serde//hmrFuzzSerdeStep" failed after 3 retries: Class "HmrFuzzBox" not found. Make sure the class is registered with registerSerializationClass.

Cause is this static classId. The SWC plugin emits a registration IIFE next to every class carrying the serialize/deserialize symbols:

__wf_reg.set(__wf_id, __wf_cls); if (!Object.prototype.hasOwnProperty.call(__wf_cls, "classId")) Object.defineProperty(__wf_cls, "classId", { value: __wf_id, ... });

The .set() is unconditional under the path-derived id, but the defineProperty is guarded by hasOwnProperty. A class that declares its own static classId keeps it. So the registry holds only class//./workflows/hmr-fuzz-serde//HmrFuzzBox while HmrFuzzBox.classId stays 'HmrFuzzBox'. The serialize reducer stamps constructor.classId into the payload, and deserialize looks that exact string up, finds nothing, and throws the message above.

I drove the real prebuilt plugin over this fixture and ran the runtime's reducer pair against the output, with and without the static, in both plugin modes:

fixture mode result

with static classId step throws Class "HmrFuzzBox" not found

with static classId workflow throws Class "HmrFuzzBox" not found

without static classId step round-trips

without static classId workflow round-trips

Attribution, since it is not obvious from the diff: this line is inherited from #3470, where it is inert. On the base branch HmrFuzzBox is constructed and compared but never crosses a step boundary, so the reducer never runs and #3470 is E2E-green. This PR adds hmrFuzzSerdeStep (here and at line 1108) plus five await hmrFuzzSerdeStep(new HmrFuzzBox(workflowValue)) call sites, which is the first code to serialize the class. The latent poisoned id becomes fatal here.

Fix: drop static classId from both fixture copies (this one and the one at line 1095). That matches the working precedent in workbench/example/workflows/serde-models.ts, where Vector declares only the two symbol statics and lets the plugin assign the id.

VaguelySerious · 2026-09-16T01:28:48Z

+                kind: 'workflow',
+                value: `serde-body-${iteration}`,
+              }) satisfies ExpectedWorkflowResult,
            source: (iteration: number) => `export class HmrFuzzBox {


AI Review: Note

The HmrFuzzBox fixture source is written out verbatim at two sites in this file (here and around line 1094), and the hmrFuzzSerdeStep call appears at five places. When the blocking fix above lands, all copies have to change together or half the matrix keeps failing. A single shared template string for the serde fixture would make that a one-line edit and remove the class of bug where the two copies drift.

VaguelySerious · 2026-09-16T01:32:10Z

AI Review: Note

Separate from the review above, on the other red check: Unit Tests (windows-latest) (job 104181466190) fails one test out of 19 files, and it is in a package this stack does not touch.

FAIL  src/storage.test.ts > Storage > concurrent entity-creation races > converges same-hook creation across separate storage instances to one event
AssertionError: expected [ { …(7) }, { …(7) }, { …(7) }, …(23) ] to have a length of 25 but got 26
 ❯ src/storage.test.ts:4444:27

Why I read this as pre-existing rather than caused by the stack:

The three-PR stack's diff against main is 23 files, none under packages/world-local.
git diff --stat origin/main <head> -- packages/world-local packages/world/src is empty, so the package is byte-identical to main at this head.
No world-local commits landed on main since the merge-base, so the branch is not missing a fix.
Unit Tests (windows-latest) was green on the last eight main runs of tests.yml, and has never failed on any prior run of the three stack branches.
The test itself dates to fix(world-local,world-postgres): make duplicate hook_created idempotent #2295 (2026-06-11).

The symptom is worth recording for whoever owns the flake: every one of the 25 iterations passed its per-iteration assertions (exactly one fulfilled, exactly one rejected with EntityConflictError), yet 26 hook_created events were persisted. A loser rejected and still published its event. That is the duplicate-publication case the test was written to catch, so it looks like a underlying race in the cross-instance convergence path rather than a bad assertion.

Caveat on the evidence: eight green main runs bounds nothing about the rate, and I did not scan all of history for this test name. The load-bearing part is non-causality (identical code, zero touched files), not the green sample.

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NathanColosimo and others added 12 commits August 28, 2026 14:27

test(next): cover HMR rebuild convergence

98095e4

test(next): cover latest stable and canary

d45b0ab

test(next): await lazy route userland

44ba779

test(next): narrow HMR expectations

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test(next): update canary coverage

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test(next): require non-source rediscovery

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test(next): assert minimal HMR rebuilds

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test(next): exercise serde HMR across a step

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ci: centralize Next canary setup

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Merge commit '43bf5b3b87' into peter/wt-3471

da9995c

# Conflicts: # .github/workflows/tests.yml # packages/next/package.json # pnpm-lock.yaml # workbench/nextjs-turbopack/package.json # workbench/nextjs-webpack/package.json

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[next] Cover hybrid serializer + step modules across dev HMR #4612

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fixture	mode	result
with `static classId`	step	throws `Class "HmrFuzzBox" not found`
with `static classId`	workflow	throws `Class "HmrFuzzBox" not found`
without `static classId`	step	round-trips
without `static classId`	workflow	round-trips

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Summary

Testing

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🧪 E2E Test Results

⚠️ Flaky E2E Tests (passed on retry)

🛠 Infra Events (absorbed by the harness)

E2E Test Summary

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📊 Workflow Benchmarks

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