[core] Trace fresh workflow replay phases

[NathanColosimo]

Summary

Added spans:

• workflow.vm.create_context — Node VM context creation plus sandbox globals and runtime shims.
• workflow.bundle.compile — obtains or creates cached vm.Script objects. Attribute: workflow.bundle.compile.cache_hit.
• workflow.bundle.evaluate — evaluates the compiled bundle inside the new context and retrieves the selected workflow function. This is bundle initialization, not yet the workflow invocation.
• workflow.input.hydrate — residual payload preparation plus deserializing workflow arguments into VM-local values.
• workflow.replay.execute — invokes the workflow function and runs it until completion or suspension.

Consolidate event-loading telemetry into:

• workflow.replay.load, replacing workflow.loadEvents and workflow.loadNewEvents.
• workflow.replay.load.source identifies run_started, hook_preload, events_list, or events_list_incremental.
• It includes event count, page count, and run ID.

Example trace:
https://app.datadoghq.com/apm/trace/62f35f6770aaca587c38cedc1701b837?graphType=waterfall&shouldShowLegend=true&spanID=3288444199644122217&traceQuery=

[changeset-bot]

🦋 Changeset detected

Latest commit: 2f331e9

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

This PR includes changesets to release 16 packages

Name	Type
@workflow/core	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

[vercel]

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 31, 2026 6:48pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 31, 2026 6:48pm
example-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workbench-astro-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workbench-express-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workbench-hono-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workbench-python-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workbench-vite-workflow	Ready	Preview, v0	Aug 31, 2026 6:48pm
workflow-docs	Ready	Preview, v0	Aug 31, 2026 6:48pm
workflow-swc-playground	Ready	Preview, v0	Aug 31, 2026 6:48pm
workflow-tarballs	Ready	Preview, v0	Aug 31, 2026 6:48pm
workflow-web	Ready	Preview, v0	Aug 31, 2026 6:48pm

[github-actions]

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

• promiseAllWorkflow | wrun_41M1CJANMV0GY4KDRE1M0WCAQ8 | 🔍 observability
• sleepingWorkflow | wrun_41M1CJBBQE0GTWCZMZZCK371E7 | 🔍 observability
• parallelSleepWorkflow | wrun_41M1CJBC5K0GXVZ7QH7SAZCZCY | 🔍 observability
• nullByteWorkflow | wrun_41M1CJBN7M0GTPETSQZY63R7Z5 | 🔍 observability
• cancelRun - cancelling a running workflow | wrun_41M1CJKNEQ0GP084V9F3P90P9T | 🔍 observability
• cancelRun via CLI - cancelling a running workflow | wrun_41M1CJKS4F0GK7Y68RZ0ZB79JR | 🔍 observability
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M1CJKZFB0GPRFV49EDRAM5SH | 🔍 observability
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M1CJMJ0F0GPGTQXM10J1MN92 | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

• deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M1CJMSX2F3FYMB3EAX08N6Z7
• promiseAllWorkflow | wrun_41M1CJANMV0GY4KDRE1M0WCAQ8
• sleepingWorkflow | wrun_41M1CJBBQE0GTWCZMZZCK371E7
• parallelSleepWorkflow | wrun_41M1CJBC5K0GXVZ7QH7SAZCZCY
• nullByteWorkflow | wrun_41M1CJBN7M0GTPETSQZY63R7Z5
• cancelRun - cancelling a running workflow | wrun_41M1CJKNEQ0GP084V9F3P90P9T
• cancelRun via CLI - cancelling a running workflow | wrun_41M1CJKS4F0GK7Y68RZ0ZB79JR
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M1CJKZFB0GPRFV49EDRAM5SH
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M1CJMJ0F0GPGTQXM10J1MN92

⚠️ 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 (express)
• addTenWorkflow (fastify)
• cancelRun via CLI - cancelling a running workflow (nextjs-turbopack)
• cancelRun via CLI - cancelling a running workflow (nextjs-webpack)
• hookWithSleepFinalStepWorkflow - step only on final payload (nextjs-turbopack)
• hookWorkflow (tanstack-start)
• hookWorkflow (vite)

🛠 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.

36 infra events

• cold-start-warmup · suite warmup (python) · at 18:48:37Z · abandoned wrun_41M1CJA5PA0GMYFQ40F5SBDPGA · (+7 more)
• run-pickup-stall · parallelSleepWorkflow (python) · at 18:48:54Z · abandoned wrun_41M1CJDTRH0GVFT0F2ZJAJ6JVW
• run-pickup-stall · sleepingWorkflow (python) · at 18:48:54Z · abandoned wrun_41M1CJDTRH0GVFT0F2ZJAJ6JVV
• run-pickup-stall · promiseAllWorkflow (python) · at 18:48:54Z · abandoned wrun_41M1CJDTRA0GHCEP8T90GZMJ89
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 18:48:55Z · abandoned wrun_41M1CJDV8K0GH9QQFJXVBYZKKA
• run-pickup-stall · nullByteWorkflow (python) · at 18:48:55Z · abandoned wrun_41M1CJDTRN0GT2WBPM146V4N17
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 18:49:28Z · abandoned wrun_41M1CJEVNV0GVA6WTKJHGYXXH7
• run-pickup-stall · sleepingWorkflow (python) · at 18:49:55Z · abandoned wrun_41M1CJFPEF0GTXPECMRV6D6D46
• run-pickup-stall · promiseAllWorkflow (python) · at 18:49:55Z · abandoned wrun_41M1CJFPMX0GY4W9F7YV56PHFM
• run-pickup-stall · parallelSleepWorkflow (python) · at 18:49:55Z · abandoned wrun_41M1CJFPSV0GG7597NZSJC3E76
• run-pickup-stall · nullByteWorkflow (python) · at 18:49:55Z · abandoned wrun_41M1CJFPHQ0GMSW4DEDBV5XKFC
• cold-start-warmup · suite warmup (tanstack-start) · at 18:50:37Z · abandoned wrun_01M1CJGMC81TX09D48WA1ENMTF
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 18:50:46Z · abandoned wrun_41M1CJFVVS0GWRHNQVR8PANNCP
• cold-start-warmup · suite warmup (python) · at 18:51:11Z · abandoned wrun_01M1CJEVFE4P9YRK09XGN9JVZ9 · (+7 more)
• run-pickup-stall · promiseAllWorkflow (python) · at 18:51:26Z · abandoned wrun_01M1CJJGKZ3RS4B0Q9ZXF35G92
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 18:51:26Z · abandoned wrun_01M1CJJGKY064CT9ABZEDRTV8D
• run-pickup-stall · parallelSleepWorkflow (python) · at 18:51:26Z · abandoned wrun_01M1CJJGM6DA1GDVSY4CTPRBAK
• run-pickup-stall · nullByteWorkflow (python) · at 18:51:26Z · abandoned wrun_01M1CJJGM85AHQZN56SSEMS10G
• run-pickup-stall · sleepingWorkflow (python) · at 18:51:26Z · abandoned wrun_01M1CJJGM4505CSRHXVP0JA7VQ
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 18:52:26Z · abandoned wrun_01M1CJMB7NR952BNJJ9Y36Y5MV
• run-pickup-stall · promiseAllWorkflow (python) · at 18:52:26Z · abandoned wrun_01M1CJMB7RQNN5CEJH4WEH47E0
• run-pickup-stall · sleepingWorkflow (python) · at 18:52:26Z · abandoned wrun_01M1CJMB7TGW2N2758ACA57K7G
• run-pickup-stall · parallelSleepWorkflow (python) · at 18:52:26Z · abandoned wrun_01M1CJMB7YA8Q1K68XZ6ZFEVXA
• run-pickup-stall · nullByteWorkflow (python) · at 18:52:26Z · abandoned wrun_01M1CJMB84PRWBWN0GS7XQJCNB
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 18:52:28Z · abandoned wrun_41M1CJJEB10GTRDWR7V9QMHRW9
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 18:52:29Z · abandoned wrun_41M1CJJKRB0GJT73JEA574CN8S
• run-pickup-stall · AllInOneService.processNumber - static workflow method using sibling static step methods (nuxt) · at 18:52:45Z · abandoned wrun_01M1CJMXWGWSBF7TNZ1B081D0X
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 18:53:26Z · abandoned wrun_01M1CJP5VAYZEM6JG8DCT2PEFS
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 18:53:26Z · abandoned wrun_01M1CJP5VM97NA91NQHNSX4M7P
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 18:53:26Z · abandoned wrun_01M1CJP5VP2GCEM7MAMP66K502
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 18:53:56Z · abandoned wrun_01M1CJQ36R46QRKSCR3KZNAME7
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 18:53:56Z · abandoned wrun_01M1CJQ36YVHMQGE9AA336EW7Y
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 18:54:26Z · abandoned wrun_01M1CJR0EVWJD8GF2CCN6YH8FX
• run-pickup-stall · hookWithSleepWorkflow - hook payloads delivered correctly with concurrent sleep (nextjs-webpack) · at 18:57:44Z · abandoned wrun_01M1CJY2BMF5X1Y6X7SPFXV67E
• run-pickup-stall · hookWithSleepFinalStepWorkflow - step only on final payload (nextjs-webpack) · at 18:57:50Z · abandoned wrun_01M1CJY7J9B0FXKM0ETSQ9Z8MG
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (nextjs-webpack) · at 18:57:50Z · abandoned wrun_01M1CJY7VMT336KMJCJCXRY8K9

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	3570	8	742	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	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	17053	17	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	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

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	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

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	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

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

❌ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
❌ python	0	9	132

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

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

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit 2f331e9 · Mon, 31 Aug 2026 19:11:43 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1255 (+46%) 🔻	1359 🔴 (+9.8%)	1393 🔴 (+7.8%)	1599 🔴 (+2.6%)	30
TTFS	stream	254 (±0%)	1396 🔴 (+9.9%)	1416 🔴 (+5.9%)	1688 🔴 (+20%) 🔻	30
TTFS	hook + stream	1247 (+121%) 🔻	1648 🔴 (+16%) 🔻	1726 🔴 (+6.6%)	1866 🔴 (-11%)	30
Fan-out TTFS	Promise.all(100 steps)	564 (+9.7%)	1968 (+9.3%)	2060 (+9.2%)	2409 (+8.0%)	10
Fan-out TTLS	Promise.all(100 steps)	1955 (-1.8%)	4417 (+4.3%)	4543 (-3.7%)	10108 (+25%) 🔻	10
STSO	1020 steps (inline)	87 (+13%)	149 (+4.2%)	166 (+1.2%)	221 (-1.3%)	1019
WO	1020 steps	143457 (±0%)	143457 (±0%)	143457 (±0%)	143457 (±0%)	1
CRTT	first chunk (pooled)	94 (-15%)	153 (-8.9%)	406 (+101%) 🔻	472 (+54%) 🔻	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	126 (-17%)	176 (-2%)	306 (+8%)	4308 (+641%)	174 (+18%)	10
size sweep (100/s, 160B-12KB)	148 (+6%)	161 (-18%)	233 (-48%)	443 (-51%)	107 (-40%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	141 (-2%)	138 (-33%)	169 (-95%)	282 (-94%)	143 (-70%)	3
replay eve-gpt-5.6-sol-2000t (1x)	173 (-32%)	5703 (+3086%)	11628 (+4827%)	15356 (+1975%)	7537 (+1096%)	2
replay eve-gpt-5.6-sol-2000t (2x)	105 (-37%)	190 (-19%)	274 (-23%)	635 (+5%)	250 (-24%)	3

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

1020 steps (inline)

Cumulative STSO time: main 143115ms → this run 142895ms (Δ -220ms, 0%)

 50-100 ms  ┃                         main   1  this   1    +0
100-150 ms  █████████████████████┃██  main 838  this 769   -69
150-200 ms  █████░┃                   main 163  this 227   +64
200-250 ms  ┃                         main   8  this  20   +12
250-300 ms  ┃                         main   4  this   1    -3
300-350 ms  ┃                         main   3  this   1    -2
350-400 ms  ┃                         main   2  this   0    -2

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

variant  RTT 1ms→5s+               avg         p50             p90             p99     n
control  ······▃█▂··▁·    302.3 (+97%)  123 (-11%)       306 (+8%)    4308 (+641%)  3000
sweep    ······▃█▁····    136.2 (-20%)  124 (-11%)      233 (-48%)      443 (-51%)  3000
gw 1x    ·····▁▄█▁····    119.6 (-66%)  114 (-23%)      169 (-95%)      282 (-94%)  5295
eve 1x   ·····▁▇█▂▁▁▁▃  1644.5 (+913%)  105 (-26%)  11628 (+4827%)  15356 (+1975%)  5186
eve 2x   ·····▁▃█▂▁···    147.8 (-23%)  131 (-22%)      274 (-23%)       635 (+5%)  7779

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

control  ▁▁▁▂▂▅█▇▇▆  120–542ms
sweep    █▃▄▂▁▂▁▁▂▁  121–189ms
gw 1x    ▅▃▅██▄▃▅▁▁  109–130ms
eve 1x   ▁▁█▇▄▂▁▁▁▁  103–6325ms
eve 2x   ▂▂█▁▃▁▃▅▁▁  130–200ms

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

sweep  █▅▃▃▂▁▅  134–140ms

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

control  ▁▁▂▂▂█▂▁▁▁  33–119ms
sweep    ▁▅▇▆▆▇▆██▇  35–57ms
gw 1x    ▄▅▇▃█▆▆█▂▁  31–42ms
eve 1x   ▁▁█▁▁▁▁▁▁▁  21–169ms
eve 2x   ▅█▇▅█▄▃▂▁▇  20–27ms

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]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.4 KiB (±0)	1.76 MiB (+886 B)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	764.9 KiB (+594 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.

2f331e9 · run

[alangenfeld]

do you have an example of what this ends up looking like?

preserve the active workflow trace across retained VM resumptions

in particular sounds like it could create hard to parse traces but theres a good chance im not interpreting it correctly

[alangenfeld]

noice

[github-actions]

No backport to stable for 1c28eec (AI decision).

This commit adds new observability surface — five new spans (workflow.vm.create_context, workflow.bundle.compile, workflow.bundle.evaluate, workflow.input.hydrate, workflow.replay.execute), new semantic-convention attributes, and a renamed/consolidated workflow.replay.load span — which is feature work rather than a fix to broken behavior on stable. It also reshapes internal APIs (getCachedWorkflowScript now returns { script, cacheHit }, runCachedWorkflowScript removed) and renames existing spans (workflow.loadEvents/workflow.loadNewEvents), a behavior change for anyone querying those span names. The only fix-like part is describeThrownValue, which keeps span status handling safe when a non-Error value is thrown; a human could split that out and force it through via workflow_dispatch if desired.

To override, re-run the Backport to stable workflow manually via workflow_dispatch and paste this commit SHA into the ref input:

1c28eeca159f022c73912326baf78d69152db876