feat(streams): add bounded WebSocket write pipelining by alangenfeld · Pull Request #3890 · vercel/workflow

alangenfeld · 2026-08-28T21:38:32Z

Summary & Motivation

Bounded write pipelining: a session may advertise up to 4 active groups, which overlaps small durable groups without adding dwell and keeps every active group counted against the existing chunk and byte bounds.

Test Plan

Tests added.

changeset-bot · 2026-08-28T21:38:36Z

🦋 Changeset detected

Latest commit: dcdabcd

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

This PR includes changesets to release 20 packages

Name	Type
@workflow/core	Minor
@workflow/world	Minor
@workflow/world-vercel	Minor
@workflow/builders	Patch
@workflow/cli	Patch
@workflow/next	Patch
@workflow/nitro	Patch
@workflow/vitest	Patch
@workflow/web-shared	Patch
@workflow/web	Patch
workflow	Minor
@workflow/world-testing	Patch
@workflow/world-local	Patch
@workflow/world-postgres	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

vercel · 2026-08-28T21:38:49Z

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

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, v0	Aug 28, 2026 10:47pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 28, 2026 10:47pm
example-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-astro-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-express-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-hono-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-python-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-vite-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workflow-docs	Ready	Preview, v0	Aug 28, 2026 10:47pm
workflow-swc-playground	Ready	Preview, v0	Aug 28, 2026 10:47pm
workflow-tarballs	Ready	Preview, v0	Aug 28, 2026 10:47pm
workflow-web	Ready	Preview, v0	Aug 28, 2026 10:47pm

github-actions · 2026-08-28T21:38:55Z

📊 Workflow Benchmarks

commit dcdabcd · Fri, 28 Aug 2026 23:01:55 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1211 (+78%) 🔻	1288 🔴 (+14%)	1301 🔴 (+14%)	1589 🔴 (+38%) 🔻	30
TTFS	stream	172 (-25%) 💚	1264 🔴 (+17%) 🔻	1282 🔴 (+16%) 🔻	1419 🔴 (+21%) 🔻	30
TTFS	hook + stream	443 (-9.6%)	1555 🔴 (+15%) 🔻	1600 🔴 (+16%) 🔻	1730 🔴 (+19%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	622 (+10%)	1671 (-2.2%)	1786 (-1.7%)	1846 (-6.1%)	10
Fan-out TTLS	Promise.all(100 steps)	1881 (-14%)	2911 (-22%) 💚	3229 (-14%)	6821 (-13%)	10
STSO	1020 steps (inline)	103 (-8.8%)	128 (-8.6%)	147 (-8.7%)	410 (+108%) 🔻	1019
WO	1020 steps	135609 (-3.7%)	135609 (-3.7%)	135609 (-3.7%)	135609 (-3.7%)	1
CRTT	first chunk (pooled)	77 (-33%) 💚	118 (-50%) 💚	139 (-73%) 💚	954 (+44%) 🔻	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	107 (-25%)	147 (-71%)	213 (-70%)	524 (-47%)	162 (-64%)	10
size sweep (100/s, 160B-12KB)	92.5 (-48%)	116 (-50%)	173 (-69%)	365 (-59%)	98.5 (-58%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	97 (-51%)	119 (-49%)	187 (-58%)	691 (-29%)	202 (-72%)	3
replay eve-gpt-5.6-sol-2000t (1x)	521 (+34%)	114 (-80%)	149 (-92%)	291 (-93%)	287 (-87%)	2
replay eve-gpt-5.6-sol-2000t (2x)	129 (-18%)	160 (-78%)	225 (-79%)	422 (-68%)	200 (-65%)	3

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

1020 steps (inline)

Cumulative STSO time: main 139837ms → this run 135457ms (Δ -4380ms, -3%)

  100-150 ms  ██████████████████████░┃  main 857  this 934   +77
  150-200 ms  █┃██                      main 152  this  63   -89
  200-250 ms  ┃                         main   8  this   4    -4
  250-300 ms  ┃                         main   0  this   4    +4
  300-350 ms  ┃                         main   2  this   0    -2
  350-400 ms  ┃                         main   0  this   2    +2
  400-450 ms  ┃                         main   0  this   2    +2
  500-550 ms  ┃                         main   0  this   2    +2
  650-700 ms  ┃                         main   0  this   1    +1
  700-750 ms  ┃                         main   0  this   2    +2
  750-800 ms  ┃                         main   0  this   1    +1
  850-900 ms  ┃                         main   0  this   1    +1
  900-950 ms  ┃                         main   0  this   1    +1
1100-1150 ms  ┃                         main   0  this   1    +1
1150-1200 ms  ┃                         main   0  this   1    +1

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

variant  RTT 1ms→5s+             avg         p50         p90         p99     n
control  ······██▂▁···  117.5 (-58%)  103 (-46%)  213 (-70%)  524 (-47%)  3000
sweep    ·····▁█▆▁····  101.2 (-51%)   95 (-45%)  173 (-69%)  365 (-59%)  3000
gw 1x    ·····▁█▄▁▁···  105.6 (-48%)   94 (-42%)  187 (-58%)  691 (-29%)  5295
eve 1x   ·····▁█▅▁▁···   97.3 (-77%)   85 (-53%)  149 (-92%)  291 (-93%)  5186
eve 2x   ·····▁▅█▂▁···  126.1 (-67%)  110 (-55%)  225 (-79%)  422 (-68%)  7779

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

control  ▅▆▇▅▂▅▂▁█▇  97–135ms
sweep    ▂▅▁█▄▃▃▂▁▄  94–117ms
gw 1x    ▄▃▃▂▁▄█▃▃▄  86–142ms
eve 1x   ▂▂▂▃▂▂█▇▆▁  90–110ms
eve 2x   ▁▂▂▆▁▅▄█▃▅  103–161ms

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

sweep  ▇█▅▃▂▁▁  99–105ms

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

control  ▂▅▅▄▃▇▁▃█▄  30–40ms
sweep    ▁▁▅█▆▅▅▇▄▆  31–45ms
gw 1x    ▆▆▄▁▂▅█▅▃▄  24–34ms
eve 1x   ▁▆▃▂▅▃█▇▄▇  19–24ms
eve 2x   ▃▃▂▅▃▃▅▁▄█  18–25ms

📜 Previous results (1)

`5f008f3`

Fri, 28 Aug 2026 22:03:00 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	179 (-74%) 💚	1283 🔴 (+13%)	1384 🔴 (+21%) 🔻	1491 🔴 (+30%) 🔻	30
TTFS	stream	159 (-31%) 💚	1412 🔴 (+31%) 🔻	1431 🔴 (+30%) 🔻	1489 🔴 (+27%) 🔻	30
TTFS	hook + stream	1560 (+218%) 🔻	1668 🔴 (+24%) 🔻	1705 🔴 (+23%) 🔻	1855 🔴 (+27%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	620 (+10%)	2126 (+24%) 🔻	2191 (+21%) 🔻	2228 (+13%)	10
Fan-out TTLS	Promise.all(100 steps)	1897 (-14%)	3992 (+7.6%)	4140 (+10.0%)	6811 (-13%)	10
STSO	1020 steps (inline)	115 (+1.8%)	143 (+2.1%)	161 (±0%)	252 (+28%) 🔻	1019
WO	1020 steps	141846 (+0.7%)	141846 (+0.7%)	141846 (+0.7%)	141846 (+0.7%)	1
CRTT	first chunk (pooled)	89 (-23%) 💚	154 (-34%) 💚	206 (-59%) 💚	376 (-43%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	125 (-13%)	148 (-70%)	207 (-71%)	344 (-65%)	134 (-70%)	10
size sweep (100/s, 160B-12KB)	139 (-22%)	157 (-33%)	216 (-62%)	745 (-17%)	153 (-35%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	152 (-22%)	130 (-44%)	164 (-63%)	269 (-72%)	213 (-71%)	3
replay eve-gpt-5.6-sol-2000t (1x)	270 (-31%)	137 (-76%)	177 (-90%)	428 (-89%)	460 (-79%)	2
replay eve-gpt-5.6-sol-2000t (2x)	125 (-20%)	197 (-73%)	281 (-73%)	773 (-42%)	219 (-61%)	3

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 · 2026-08-28T21:38:55Z

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

promiseAllWorkflow | wrun_41M158XHDZ0GSPBXQZT2FRCFAC | 🔍 observability
sleepingWorkflow | wrun_41M158Y58Y0GZGG9YBTFNK2CGE | 🔍 observability
parallelSleepWorkflow | wrun_41M158Y7GW0GV4P2EF0AYTRMJ5 | 🔍 observability
nullByteWorkflow | wrun_41M158YE730GMKH1NX5NVGCJQ8 | 🔍 observability
cancelRun - cancelling a running workflow | wrun_41M1592RD80GT2DXFKPXEQMCPN | 🔍 observability
cancelRun via CLI - cancelling a running workflow | wrun_41M1592YXB0GM4VB3D0H3CBS91 | 🔍 observability
sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M159332C0GKQDYVH9JMZ10R9 | 🔍 observability
resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M1593KBE0GWX6W610XW3TZ0V | 🔍 observability

💻 Local Development (1 failed)

vite-stable-node (1 failed):

hookWorkflow | wrun_41M158XTBC0GW4BP9DSF6JSXJ2

🪟 Windows (1 failed)

nextjs-turbopack-node (1 failed):

hookWithSleepFinalStepWorkflow - step only on final payload | wrun_41M159316N0GSHHTHQD5ZH9PM0

🌐 Cross-language Conformance (9 failed)

python (9 failed):

deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M15964CXNHK82XZJQ6KV6FQD
promiseAllWorkflow | wrun_41M158XHDZ0GSPBXQZT2FRCFAC
sleepingWorkflow | wrun_41M158Y58Y0GZGG9YBTFNK2CGE
parallelSleepWorkflow | wrun_41M158Y7GW0GV4P2EF0AYTRMJ5
nullByteWorkflow | wrun_41M158YE730GMKH1NX5NVGCJQ8
cancelRun - cancelling a running workflow | wrun_41M1592RD80GT2DXFKPXEQMCPN
cancelRun via CLI - cancelling a running workflow | wrun_41M1592YXB0GM4VB3D0H3CBS91
sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M159332C0GKQDYVH9JMZ10R9
resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M1593KBE0GWX6W610XW3TZ0V

⚠️ 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.

addTenWorkflow (hono)
addTenWorkflow (sveltekit)
addTenWorkflow (vite)
cancelRun via CLI - cancelling a running workflow (fastify)
deploymentId: 'latest' is a no-op in non-Vercel worlds (sveltekit)
hookWorkflow (tanstack-start)
RetryableError respects custom retryAfter delay (nextjs-turbopack)
should work with react rendering in step (nextjs-webpack)

🛠 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.

34 infra events

cold-start-warmup · suite warmup (python) · at 22:48:01Z · abandoned wrun_41M158TBJ40GHCB2Z5EFMY3KSV · (+7 more)
run-pickup-stall · nullByteWorkflow (python) · at 22:48:17Z · abandoned wrun_41M158Y0HR0GQWZYNR2KAP06SV
run-pickup-stall · promiseAllWorkflow (python) · at 22:48:17Z · abandoned wrun_41M158Y0HE0GZP33T0S3Q9JRJW
run-pickup-stall · parallelSleepWorkflow (python) · at 22:48:18Z · abandoned wrun_41M158Y0HM0GYAATQ1Q9VA00J5
run-pickup-stall · sleepingWorkflow (python) · at 22:48:18Z · abandoned wrun_41M158Y0HM0GYAATQ1Q9VA00J4
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:48:18Z · abandoned wrun_41M158Y0ZY0GJ3AR3BXAND7H2K
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:48:51Z · abandoned wrun_41M158Z15F0GVW8NS3QPXWSJ5W
run-pickup-stall · parallelSleepWorkflow (python) · at 22:49:18Z · abandoned wrun_41M158ZWAZ0GHWAQVPGVXD3N0Y
run-pickup-stall · sleepingWorkflow (python) · at 22:49:19Z · abandoned wrun_41M158ZW8C0GQBQPZKT4X28FHY
run-pickup-stall · nullByteWorkflow (python) · at 22:49:19Z · abandoned wrun_41M158ZWDV0GVTN0YRX84JWW1S
run-pickup-stall · promiseAllWorkflow (python) · at 22:49:19Z · abandoned wrun_41M158ZWBH0GRRRH6EMEM5A8T9
cold-start-warmup · suite warmup (tanstack-start) · at 22:50:07Z · abandoned wrun_01M159113KA0MHSCD3FCEWSK2P
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:50:10Z · abandoned wrun_41M159015W0GP25NW18JG8M12W
cold-start-warmup · suite warmup (python) · at 22:51:12Z · abandoned wrun_01M15905Z2QFGAQS7YSB8VHHQ9 · (+7 more)
run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:51:27Z · abandoned wrun_01M1593V3RCBW9VRM06WZE9DHA
run-pickup-stall · promiseAllWorkflow (python) · at 22:51:27Z · abandoned wrun_01M1593V3SJWK2T008ETW5AHF1
run-pickup-stall · parallelSleepWorkflow (python) · at 22:51:27Z · abandoned wrun_01M1593V40C2QSQ5EYNNBFV5EP
run-pickup-stall · sleepingWorkflow (python) · at 22:51:27Z · abandoned wrun_01M1593V3Y5NQ32YFJ6WATY4K5
run-pickup-stall · nullByteWorkflow (python) · at 22:51:27Z · abandoned wrun_01M1593V42TM7Q4GHW8KQ0SMR1
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:51:51Z · abandoned wrun_41M1592M4X0GW1Z1E00TJAC4NC
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:51:51Z · abandoned wrun_41M1592S2C0GZ34REV6V401FJB
run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:52:27Z · abandoned wrun_01M1595NQJ1J0H2YH7RGJ4JBBY
run-pickup-stall · promiseAllWorkflow (python) · at 22:52:27Z · abandoned wrun_01M1595NQMD3W1THBJM9EG28Z6
run-pickup-stall · sleepingWorkflow (python) · at 22:52:27Z · abandoned wrun_01M1595NQR8WTTNKJ7C23477PH
run-pickup-stall · parallelSleepWorkflow (python) · at 22:52:27Z · abandoned wrun_01M1595NQTM9R6QW1W8BD2B0WY
run-pickup-stall · nullByteWorkflow (python) · at 22:52:27Z · abandoned wrun_01M1595NR2HBC6QB0F826FAZYG
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:52:42Z · abandoned wrun_41M1594QEP0GRV0MS3C0EAW97E
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:53:27Z · abandoned wrun_01M1597GBCM01ES6E8T5H3P19Z
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:53:27Z · abandoned wrun_01M1597GBFR319QKXXKQNR7WBT
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:53:27Z · abandoned wrun_01M1597GBS1CEPB8PVVX6HQWPK
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:53:57Z · abandoned wrun_01M1598DQ7Z8N713YNBSNHVFKH
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:53:57Z · abandoned wrun_01M1598DQAA1Q52G1QDMPMHXNW
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:54:27Z · abandoned wrun_01M1599AYXFXRST3ED2WWFKKTB
run-pickup-stall · hookWithSleepFinalStepWorkflow - step only on final payload (nextjs-webpack) · at 22:57:42Z · abandoned wrun_01M159F9D8TXKSR9TNX2H8770T

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	3570	8	742	4320
❌ 💻 Local Development	3921	1	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
❌ 🪟 Windows	319	1	0	320
❌ 🌐 Cross-language Conformance	0	9	132	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17051	19	2778	19848

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
❌ python-node	0	8	152
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

❌ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
❌ vite-stable-node	133	1	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Skipped
✅ astro-stable-node	134	26
✅ astro-stable-quickjs	134	26
✅ express-stable-node	134	26
✅ express-stable-quickjs	134	26
✅ fastify-stable-node	134	26
✅ fastify-stable-quickjs	134	26
✅ hono-stable-node	134	26
✅ hono-stable-quickjs	134	26
✅ nest-stable-node	134	26
✅ nest-stable-quickjs	134	26
✅ nextjs-turbopack-canary-node	141	19
✅ nextjs-turbopack-canary-quickjs	141	19
✅ nextjs-turbopack-stable-node	160	0
✅ nextjs-turbopack-stable-quickjs	160	0
✅ nextjs-webpack-canary-node	141	19
✅ nextjs-webpack-canary-quickjs	141	19
✅ nextjs-webpack-stable-node	160	0
✅ nextjs-webpack-stable-quickjs	160	0
✅ nitro-stable-node	134	26
✅ nitro-stable-quickjs	134	26
✅ nuxt-stable-node	134	26
✅ nuxt-stable-quickjs	134	26
✅ sveltekit-stable-node	153	7
✅ sveltekit-stable-quickjs	153	7
✅ tanstack-start-node	134	26
✅ tanstack-start-quickjs	134	26
✅ vite-stable-node	134	26
✅ vite-stable-quickjs	134	26

✅ 🐘 Local Postgres

App	Passed	Skipped
✅ astro-stable-node	134	26
✅ astro-stable-quickjs	134	26
✅ express-stable-node	134	26
✅ express-stable-quickjs	134	26
✅ fastify-stable-node	134	26
✅ fastify-stable-quickjs	134	26
✅ hono-stable-node	134	26
✅ hono-stable-quickjs	134	26
✅ nest-stable-node	134	26
✅ nest-stable-quickjs	134	26
✅ nextjs-turbopack-canary-node	141	19
✅ nextjs-turbopack-canary-quickjs	141	19
✅ nextjs-turbopack-stable-node	160	0
✅ nextjs-turbopack-stable-quickjs	160	0
✅ nextjs-webpack-canary-node	141	19
✅ nextjs-webpack-canary-quickjs	141	19
✅ nextjs-webpack-stable-node	160	0
✅ nextjs-webpack-stable-quickjs	160	0
✅ nitro-stable-node	134	26
✅ nitro-stable-quickjs	134	26
✅ nuxt-stable-node	134	26
✅ nuxt-stable-quickjs	134	26
✅ sveltekit-stable-node	153	7
✅ sveltekit-stable-quickjs	153	7
✅ tanstack-start-node	134	26
✅ tanstack-start-quickjs	134	26
✅ vite-stable-node	134	26
✅ vite-stable-quickjs	134	26

❌ 🪟 Windows

App	Passed	Failed	Skipped
❌ nextjs-turbopack-node	159	1	0
✅ nextjs-turbopack-quickjs	160	0	0

❌ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
❌ python	0	9	132

✅ vercel-http-transport

App	Passed	Skipped
✅ example	132	28
✅ express	132	28
✅ hono	132	28
✅ nextjs-turbopack	157	3
✅ nitro	132	28
✅ vite	132	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Skipped
✅ example	132	28
✅ express	132	28
✅ nextjs-turbopack	157	3
✅ vite	132	28

📋 View full workflow run

github-actions · 2026-08-28T21:42:11Z

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 · 2026-08-28T21:42:57Z

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.3 KiB (-99 B)	1.77 MiB (+6.3 KiB)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	768.8 KiB (+4.9 KiB)

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.

dcdabcd · run

vercel

Additional Suggestion:

The WS read session's reconnects counter is never reset on forward progress, so its MAX_WS_RECONNECTS = 3 budget bounds lifetime reconnects (including graceful server recycles) instead of consecutive failures, permanently forcing long-lived streams onto the HTTP fallback.

Signed-off-by: Alex Langenfeld <alex.langenfeld@vercel.com>

vercel Bot deployed to Preview – workbench-python-workflow August 28, 2026 21:39 View deployment

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alangenfeld force-pushed the alangenfeld/ws-stream-write-pipelining branch from 5f008f3 to bdb0a6f Compare August 28, 2026 22:26

vercel Bot deployed to Preview – workbench-python-workflow August 28, 2026 22:26 View deployment

vercel Bot deployed to Preview – workflow-web August 28, 2026 22:27 View deployment

vercel Bot deployed to Preview – workbench-hono-workflow August 28, 2026 22:27 View deployment

vercel Bot deployed to Preview – workbench-fastify-workflow August 28, 2026 22:27 View deployment

vercel Bot deployed to Preview – workbench-express-workflow August 28, 2026 22:27 View deployment

vercel Bot deployed to Preview – workbench-nestjs-workflow August 28, 2026 22:34 View deployment

vercel Bot deployed to Preview – workbench-express-workflow August 28, 2026 22:34 View deployment

vercel Bot deployed to Preview – workbench-fastify-workflow August 28, 2026 22:34 View deployment

vercel Bot deployed to Preview – workbench-hono-workflow August 28, 2026 22:34 View deployment

vercel Bot deployed to Preview – workbench-astro-workflow August 28, 2026 22:34 View deployment

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vercel Bot deployed to Preview – workbench-nitro-workflow August 28, 2026 22:34 View deployment

vercel Bot deployed to Preview – workbench-nuxt-workflow August 28, 2026 22:35 View deployment

vercel Bot deployed to Preview – example-nextjs-workflow-webpack August 28, 2026 22:35 View deployment

vercel Bot deployed to Preview – workbench-vite-workflow August 28, 2026 22:35 View deployment

vercel Bot deployed to Preview – example-nextjs-workflow-turbopack August 28, 2026 22:35 View deployment

vercel Bot deployed to Preview – example-workflow August 28, 2026 22:35 View deployment

vercel Bot deployed to Preview – workbench-tanstack-start-workflow August 28, 2026 22:35 View deployment

vercel Bot deployed to Preview – workflow-docs August 28, 2026 22:35 View deployment

vercel Bot deployed to Preview – workflow-swc-playground August 28, 2026 22:36 View deployment

vercel Bot reviewed Aug 28, 2026

View reviewed changes

feat(streams): add bounded WebSocket write pipelining

dcdabcd

Signed-off-by: Alex Langenfeld <alex.langenfeld@vercel.com>

alangenfeld force-pushed the alangenfeld/ws-stream-write-pipelining branch from e576272 to dcdabcd Compare August 28, 2026 22:44

vercel Bot deployed to Preview – workbench-python-workflow August 28, 2026 22:44 View deployment

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vercel Bot deployed to Preview – workbench-hono-workflow August 28, 2026 22:45 View deployment

vercel Bot deployed to Preview – workbench-nitro-workflow August 28, 2026 22:45 View deployment

vercel Bot deployed to Preview – workbench-express-workflow August 28, 2026 22:45 View deployment

vercel Bot deployed to Preview – workbench-vite-workflow August 28, 2026 22:46 View deployment

vercel Bot deployed to Preview – workbench-nestjs-workflow August 28, 2026 22:46 View deployment

vercel Bot deployed to Preview – workbench-tanstack-start-workflow August 28, 2026 22:46 View deployment

vercel Bot deployed to Preview – example-workflow August 28, 2026 22:46 View deployment

vercel Bot deployed to Preview – workbench-fastify-workflow August 28, 2026 22:46 View deployment

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feat(streams): add bounded WebSocket write pipelining - #3890

feat(streams): add bounded WebSocket write pipelining#3890
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Summary & Motivation

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🦋 Changeset detected

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📊 Workflow Benchmarks

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🧪 E2E Test Results

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

💻 Local Development (1 failed)

🪟 Windows (1 failed)

🌐 Cross-language Conformance (9 failed)

⚠️ Flaky E2E Tests (passed on retry)

🛠 Infra Events (absorbed by the harness)

E2E Test Summary

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Sim World

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