[ai] Drop orphan UI chunks after negative-index reconnect by VaguelySerious · Pull Request #2082 · vercel/workflow

VaguelySerious · 2026-05-22T10:34:44Z

Addressed part of #1835 by ensuring WorkflowChatTransport never fails when using startIndex between chunk boundaries, and adds an example code snippet for how to do server-side rewinds.

Issue: When WorkflowChatTransport resumes with a negative initialStartIndex, the resolved chunk index can land in the middle of an open text-* / reasoning-* / tool-input-* part. AI SDK's client enforces the *-start → *-delta → *-end grammar and throws on the orphan delta — breaking the chat.

This PR adds a one-pass filter on the resumed stream that drops chunks referencing a part whose start chunk wasn't in the resumed window, and emits a one-time warning pointing at docs on server-side rewinding. The filter only activates for negative startIndex — for non-negative values the caller is explicit and we trust them.

When `WorkflowChatTransport` resumes with a negative `initialStartIndex`, the resolved chunk can land in the middle of an open `text-*` / `reasoning-*` / `tool-input-*` part. AI SDK's client enforces the start→delta→end grammar and throws on the orphan delta, breaking the chat. Add a one-pass filter on the resumed stream that drops chunks referencing a part whose start chunk wasn't in the resumed window, and warn once with a pointer to docs on server-side rewinding. Filter only activates for negative startIndex — non-negative is the caller's explicit choice. Refs: #1835 Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

vercel · 2026-05-22T10:34:47Z

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changeset-bot · 2026-05-22T10:34:54Z

🦋 Changeset detected

Latest commit: 3bdac11

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

This PR includes changesets to release 1 package

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@workflow/ai	Patch

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github-actions · 2026-05-22T10:34:58Z

🧪 E2E Test Results

✅ All tests passed

Summary

	Passed	Skipped	Total
✅ ▲ Vercel Production	1222	219	1441
✅ 💻 Local Development	1615	219	1834
✅ 📦 Local Production	1615	219	1834
✅ 🐘 Local Postgres	1615	219	1834
✅ 🪟 Windows	131	0	131
✅ 📋 Other	741	176	917
Total	6939	1052	7991

Details by Category

✅ ▲ Vercel Production

App	Passed	Skipped
✅ astro	105	26
✅ example	105	26
✅ express	105	26
✅ fastify	105	26
✅ hono	105	26
✅ nextjs-turbopack	129	2
✅ nextjs-webpack	129	2
✅ nitro	105	26
✅ nuxt	105	26
✅ sveltekit	124	7
✅ vite	105	26

✅ 💻 Local Development

App	Passed	Skipped
✅ astro-stable	106	25
✅ express-stable	106	25
✅ fastify-stable	106	25
✅ hono-stable	106	25
✅ nextjs-turbopack-canary	112	19
✅ nextjs-turbopack-stable-lazy-discovery-disabled	131	0
✅ nextjs-turbopack-stable-lazy-discovery-enabled	131	0
✅ nextjs-webpack-canary	112	19
✅ nextjs-webpack-stable-lazy-discovery-disabled	131	0
✅ nextjs-webpack-stable-lazy-discovery-enabled	131	0
✅ nitro-stable	106	25
✅ nuxt-stable	106	25
✅ sveltekit-stable	125	6
✅ vite-stable	106	25

✅ 📦 Local Production

App	Passed	Skipped
✅ astro-stable	106	25
✅ express-stable	106	25
✅ fastify-stable	106	25
✅ hono-stable	106	25
✅ nextjs-turbopack-canary	112	19
✅ nextjs-turbopack-stable-lazy-discovery-disabled	131	0
✅ nextjs-turbopack-stable-lazy-discovery-enabled	131	0
✅ nextjs-webpack-canary	112	19
✅ nextjs-webpack-stable-lazy-discovery-disabled	131	0
✅ nextjs-webpack-stable-lazy-discovery-enabled	131	0
✅ nitro-stable	106	25
✅ nuxt-stable	106	25
✅ sveltekit-stable	125	6
✅ vite-stable	106	25

✅ 🐘 Local Postgres

App	Passed	Skipped
✅ astro-stable	106	25
✅ express-stable	106	25
✅ fastify-stable	106	25
✅ hono-stable	106	25
✅ nextjs-turbopack-canary	112	19
✅ nextjs-turbopack-stable-lazy-discovery-disabled	131	0
✅ nextjs-turbopack-stable-lazy-discovery-enabled	131	0
✅ nextjs-webpack-canary	112	19
✅ nextjs-webpack-stable-lazy-discovery-disabled	131	0
✅ nextjs-webpack-stable-lazy-discovery-enabled	131	0
✅ nitro-stable	106	25
✅ nuxt-stable	106	25
✅ sveltekit-stable	125	6
✅ vite-stable	106	25

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack	131	0	0

✅ 📋 Other

App	Passed	Skipped
✅ e2e-local-dev-nest-stable	106	25
✅ e2e-local-dev-tanstack-start-	106	25
✅ e2e-local-postgres-nest-stable	106	25
✅ e2e-local-postgres-tanstack-start-	106	25
✅ e2e-local-prod-nest-stable	106	25
✅ e2e-local-prod-tanstack-start-	106	25
✅ e2e-vercel-prod-tanstack-start	105	26

📋 View full workflow run

github-actions · 2026-05-22T10:35:02Z

📊 Benchmark Results

📈 Comparing against baseline from main branch. Green 🟢 = faster, Red 🔺 = slower.

workflow with no steps

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
💻 Local	🥇 Express	0.030s (-31.8% 🟢)	1.006s (~)	0.976s	10	1.00x
💻 Local	Nitro	0.031s (-29.0% 🟢)	1.005s (~)	0.975s	10	1.01x
💻 Local	Next.js (Turbopack)	0.046s	1.005s	0.959s	10	1.54x
🐘 Postgres	Nitro	0.048s (-49.2% 🟢)	1.013s (-2.9%)	0.964s	10	1.60x
🐘 Postgres	Express	0.051s (-11.6% 🟢)	1.013s (~)	0.962s	10	1.70x
🐘 Postgres	Next.js (Turbopack)	0.055s	1.012s	0.956s	10	1.83x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	0.233s (-7.6% 🟢)	1.809s (-22.5% 🟢)	1.577s	10	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

workflow with 1 step

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
💻 Local	🥇 Nitro	1.071s (-5.3% 🟢)	2.006s (~)	0.935s	10	1.00x
💻 Local	Express	1.075s (-4.5%)	2.006s (~)	0.932s	10	1.00x
🐘 Postgres	Express	1.081s (-5.7% 🟢)	2.008s (~)	0.927s	10	1.01x
🐘 Postgres	Nitro	1.087s (-4.6%)	2.009s (~)	0.922s	10	1.02x
💻 Local	Next.js (Turbopack)	1.112s	2.006s	0.894s	10	1.04x
🐘 Postgres	Next.js (Turbopack)	1.119s	2.008s	0.889s	10	1.05x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	1.704s (-16.3% 🟢)	6.835s (+78.4% 🔺)	5.131s	10	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

workflow with 10 sequential steps

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	10.403s (-5.1% 🟢)	11.018s (~)	0.615s	3	1.00x
💻 Local	Nitro	10.407s (-4.9%)	11.022s (~)	0.616s	3	1.00x
🐘 Postgres	Nitro	10.417s (-4.2%)	11.010s (~)	0.593s	3	1.00x
💻 Local	Express	10.423s (-4.6%)	11.022s (~)	0.599s	3	1.00x
🐘 Postgres	Next.js (Turbopack)	10.710s	11.017s	0.306s	3	1.03x
💻 Local	Next.js (Turbopack)	10.718s	11.021s	0.304s	3	1.03x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	14.105s (-18.6% 🟢)	16.246s (-16.3% 🟢)	2.141s	2	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

workflow with 25 sequential steps

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	13.454s (-7.7% 🟢)	14.019s (-6.7% 🟢)	0.564s	5	1.00x
🐘 Postgres	Nitro	13.482s (-7.6% 🟢)	14.015s (-6.7% 🟢)	0.532s	5	1.00x
💻 Local	Express	13.488s (-9.9% 🟢)	14.026s (-6.7% 🟢)	0.538s	5	1.00x
💻 Local	Nitro	13.490s (-10.4% 🟢)	14.027s (-12.5% 🟢)	0.537s	5	1.00x
💻 Local	Next.js (Turbopack)	14.057s	15.030s	0.973s	4	1.04x
🐘 Postgres	Next.js (Turbopack)	14.156s	15.016s	0.860s	4	1.05x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	23.299s (-55.7% 🟢)	25.425s (-53.4% 🟢)	2.125s	3	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

workflow with 50 sequential steps

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	11.907s (-15.0% 🟢)	12.140s (-16.8% 🟢)	0.233s	8	1.00x
💻 Local	Express	11.920s (-28.2% 🟢)	12.022s (-29.4% 🟢)	0.102s	8	1.00x
💻 Local	Nitro	11.950s (-28.8% 🟢)	12.396s (-27.2% 🟢)	0.447s	8	1.00x
🐘 Postgres	Nitro	11.950s (-14.4% 🟢)	12.142s (-15.1% 🟢)	0.193s	8	1.00x
🐘 Postgres	Next.js (Turbopack)	13.050s	13.872s	0.822s	7	1.10x
💻 Local	Next.js (Turbopack)	13.129s	14.027s	0.898s	7	1.10x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	34.010s (-91.4% 🟢)	36.364s (-90.8% 🟢)	2.354s	3	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

Promise.all with 10 concurrent steps

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	1.143s (-9.3% 🟢)	2.008s (~)	0.865s	15	1.00x
🐘 Postgres	Nitro	1.164s (-8.7% 🟢)	2.007s (~)	0.843s	15	1.02x
💻 Local	Nitro	1.169s (-28.4% 🟢)	2.007s (-3.3%)	0.838s	15	1.02x
💻 Local	Express	1.175s (-21.1% 🟢)	2.006s (~)	0.831s	15	1.03x
🐘 Postgres	Next.js (Turbopack)	1.211s	2.008s	0.796s	15	1.06x
💻 Local	Next.js (Turbopack)	1.283s	2.006s	0.723s	15	1.12x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	2.611s (-23.2% 🟢)	4.030s (-18.3% 🟢)	1.420s	8	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

Promise.all with 25 concurrent steps

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	1.201s (-49.1% 🟢)	2.007s (-33.3% 🟢)	0.806s	15	1.00x
🐘 Postgres	Nitro	1.221s (-48.0% 🟢)	2.007s (-33.3% 🟢)	0.786s	15	1.02x
🐘 Postgres	Next.js (Turbopack)	1.341s	2.007s	0.666s	15	1.12x
💻 Local	Nitro	1.752s (-44.3% 🟢)	2.007s (-48.3% 🟢)	0.254s	15	1.46x
💻 Local	Express	1.781s (-39.7% 🟢)	2.006s (-41.9% 🟢)	0.225s	15	1.48x
💻 Local	Next.js (Turbopack)	1.826s	2.007s	0.180s	15	1.52x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	4.093s (-42.4% 🟢)	5.800s (-34.9% 🟢)	1.707s	6	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

Promise.all with 50 concurrent steps

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	1.314s (-62.3% 🟢)	2.009s (-49.9% 🟢)	0.695s	15	1.00x
🐘 Postgres	Nitro	1.324s (-61.9% 🟢)	2.007s (-49.9% 🟢)	0.683s	15	1.01x
🐘 Postgres	Next.js (Turbopack)	1.600s	2.006s	0.406s	15	1.22x
💻 Local	Nitro	4.947s (-40.8% 🟢)	5.512s (-38.9% 🟢)	0.565s	6	3.77x
💻 Local	Express	5.118s (-38.6% 🟢)	5.679s (-37.1% 🟢)	0.561s	6	3.90x
💻 Local	Next.js (Turbopack)	5.723s	6.213s	0.490s	5	4.36x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	6.337s (-28.9% 🟢)	8.191s (-25.3% 🟢)	1.854s	4	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

Promise.race with 10 concurrent steps

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Nitro	1.149s (-8.6% 🟢)	2.008s (~)	0.860s	15	1.00x
🐘 Postgres	Express	1.151s (-8.4% 🟢)	2.008s (~)	0.857s	15	1.00x
🐘 Postgres	Next.js (Turbopack)	1.202s	2.009s	0.808s	15	1.05x
💻 Local	Next.js (Turbopack)	1.321s	2.006s	0.685s	15	1.15x
💻 Local	Nitro	1.368s (-26.7% 🟢)	2.006s (-14.3% 🟢)	0.637s	15	1.19x
💻 Local	Express	1.374s (-27.4% 🟢)	2.006s (-15.1% 🟢)	0.632s	15	1.20x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	2.785s (-5.0%)	4.318s (-7.0% 🟢)	1.533s	7	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

Promise.race with 25 concurrent steps

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	1.194s (-49.0% 🟢)	2.008s (-33.3% 🟢)	0.813s	15	1.00x
🐘 Postgres	Nitro	1.206s (-48.4% 🟢)	2.008s (-33.3% 🟢)	0.801s	15	1.01x
🐘 Postgres	Next.js (Turbopack)	1.377s	2.006s	0.629s	15	1.15x
💻 Local	Nitro	1.998s (-34.8% 🟢)	2.392s (-38.4% 🟢)	0.394s	13	1.67x
💻 Local	Express	2.053s (-34.4% 🟢)	2.508s (-33.3% 🟢)	0.455s	12	1.72x
💻 Local	Next.js (Turbopack)	2.122s	3.008s	0.887s	10	1.78x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	3.568s (+13.5% 🔺)	5.498s (+21.6% 🔺)	1.930s	6	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

Promise.race with 50 concurrent steps

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	1.315s (-62.4% 🟢)	2.007s (-50.0% 🟢)	0.691s	15	1.00x
🐘 Postgres	Nitro	1.318s (-62.1% 🟢)	2.007s (-49.9% 🟢)	0.690s	15	1.00x
🐘 Postgres	Next.js (Turbopack)	1.661s	2.073s	0.412s	15	1.26x
💻 Local	Nitro	5.818s (-36.4% 🟢)	6.415s (-36.0% 🟢)	0.596s	5	4.42x
💻 Local	Express	5.884s (-33.1% 🟢)	6.416s (-30.8% 🟢)	0.531s	5	4.47x
💻 Local	Next.js (Turbopack)	5.988s	6.416s	0.428s	5	4.55x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	5.965s (-11.7% 🟢)	7.607s (-11.0% 🟢)	1.642s	4	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

workflow with 10 sequential data payload steps (10KB)

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Nitro	0.454s (-44.7% 🟢)	1.007s (~)	0.553s	60	1.00x
💻 Local	Express	0.473s (-51.9% 🟢)	1.004s (-6.7% 🟢)	0.531s	60	1.04x
🐘 Postgres	Express	0.478s (-43.0% 🟢)	1.023s (~)	0.545s	59	1.05x
💻 Local	Nitro	0.483s (-50.7% 🟢)	1.004s (-8.2% 🟢)	0.521s	60	1.06x
🐘 Postgres	Next.js (Turbopack)	0.673s	1.006s	0.333s	60	1.48x
💻 Local	Next.js (Turbopack)	0.714s	1.005s	0.290s	60	1.57x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	5.898s (-59.3% 🟢)	7.645s (-52.5% 🟢)	1.747s	8	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

workflow with 25 sequential data payload steps (10KB)

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	1.094s (-44.7% 🟢)	1.705s (-24.5% 🟢)	0.611s	53	1.00x
🐘 Postgres	Nitro	1.136s (-41.1% 🟢)	1.986s (-5.5% 🟢)	0.850s	46	1.04x
💻 Local	Express	1.189s (-60.6% 🟢)	2.006s (-44.0% 🟢)	0.817s	45	1.09x
💻 Local	Nitro	1.219s (-59.8% 🟢)	2.006s (-46.6% 🟢)	0.787s	45	1.11x
🐘 Postgres	Next.js (Turbopack)	1.579s	2.007s	0.428s	45	1.44x
💻 Local	Next.js (Turbopack)	1.770s	2.006s	0.236s	45	1.62x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	14.683s (-70.5% 🟢)	16.947s (-67.2% 🟢)	2.264s	6	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

workflow with 50 sequential data payload steps (10KB)

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	2.015s (-49.5% 🟢)	2.360s (-46.0% 🟢)	0.345s	51	1.00x
🐘 Postgres	Nitro	2.203s (-46.3% 🟢)	2.845s (-38.2% 🟢)	0.643s	43	1.09x
💻 Local	Express	2.726s (-70.4% 🟢)	3.058s (-69.5% 🟢)	0.332s	40	1.35x
💻 Local	Nitro	2.741s (-70.5% 🟢)	3.032s (-69.7% 🟢)	0.291s	40	1.36x
🐘 Postgres	Next.js (Turbopack)	3.101s	4.008s	0.907s	30	1.54x
💻 Local	Next.js (Turbopack)	3.877s	4.108s	0.231s	30	1.92x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	27.632s (-74.2% 🟢)	29.576s (-72.8% 🟢)	1.944s	5	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

workflow with 10 concurrent data payload steps (10KB)

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Nitro	0.184s (-34.9% 🟢)	1.006s (~)	0.822s	60	1.00x
🐘 Postgres	Express	0.214s (-24.3% 🟢)	1.006s (~)	0.792s	60	1.16x
🐘 Postgres	Next.js (Turbopack)	0.225s	1.006s	0.781s	60	1.22x
💻 Local	Express	0.395s (-29.5% 🟢)	1.004s (~)	0.609s	60	2.14x
💻 Local	Nitro	0.419s (-30.7% 🟢)	1.004s (-1.7%)	0.585s	60	2.27x
💻 Local	Next.js (Turbopack)	0.547s	1.005s	0.457s	60	2.97x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	3.098s (+53.2% 🔺)	5.233s (+38.0% 🔺)	2.136s	12	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

workflow with 25 concurrent data payload steps (10KB)

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	0.292s (-42.8% 🟢)	1.006s (~)	0.714s	90	1.00x
🐘 Postgres	Nitro	0.304s (-38.8% 🟢)	1.006s (~)	0.703s	90	1.04x
🐘 Postgres	Next.js (Turbopack)	0.434s	1.006s	0.573s	90	1.49x
💻 Local	Nitro	2.141s (-15.7% 🟢)	2.714s (-9.8% 🟢)	0.573s	34	7.34x
💻 Local	Express	2.176s (-13.4% 🟢)	2.796s (-7.1% 🟢)	0.621s	33	7.46x
💻 Local	Next.js (Turbopack)	2.334s	3.010s	0.676s	30	8.00x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	6.565s (+85.7% 🔺)	8.571s (+65.0% 🔺)	2.006s	11	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

workflow with 50 concurrent data payload steps (10KB)

💻 Local Development

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	0.604s (-26.2% 🟢)	1.006s (-1.1%)	0.401s	120	1.00x
🐘 Postgres	Nitro	0.650s (-17.8% 🟢)	1.006s (~)	0.356s	120	1.07x
🐘 Postgres	Next.js (Turbopack)	0.891s	1.069s	0.178s	113	1.47x
💻 Local	Nitro	10.189s (-8.9% 🟢)	10.695s (-8.3% 🟢)	0.506s	12	16.86x
💻 Local	Express	10.262s (-8.3% 🟢)	10.777s (-9.7% 🟢)	0.514s	12	16.98x
💻 Local	Next.js (Turbopack)	10.775s	11.390s	0.615s	11	17.83x

▲ Production (Vercel)

World	Framework	Workflow Time	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	15.945s (+54.4% 🔺)	18.310s (+49.0% 🔺)	2.365s	7	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-

🔍 Observability: Next.js (Turbopack)

Stream Benchmarks (includes TTFB metrics)

workflow with stream

💻 Local Development

World	Framework	Workflow Time	TTFB	Slurp	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	1.129s (+450.7% 🔺)	2.001s (+100.3% 🔺)	0.001s (-12.5% 🟢)	2.010s (+98.7% 🔺)	0.880s	10	1.00x
💻 Local	Nitro	1.132s (+429.7% 🔺)	2.005s (+99.6% 🔺)	0.012s (-3.2%)	2.020s (+98.2% 🔺)	0.888s	10	1.00x
💻 Local	Express	1.136s (+470.5% 🔺)	2.005s (+99.6% 🔺)	0.012s (+2.5%)	2.020s (+98.4% 🔺)	0.884s	10	1.01x
🐘 Postgres	Nitro	1.147s (+459.4% 🔺)	2.000s (+100.1% 🔺)	0.001s (-20.0% 🟢)	2.010s (+98.7% 🔺)	0.863s	10	1.02x
💻 Local	Next.js (Turbopack)	1.175s	2.003s	0.013s	2.020s	0.845s	10	1.04x
🐘 Postgres	Next.js (Turbopack)	1.192s	2.001s	0.001s	2.011s	0.819s	10	1.06x

▲ Production (Vercel)

World	Framework	Workflow Time	TTFB	Slurp	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	2.357s (-65.6% 🟢)	3.697s (-57.3% 🟢)	2.371s (+275.2% 🔺)	6.508s (-33.5% 🟢)	4.151s	10	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-	-

🔍 Observability: Next.js (Turbopack)

stream pipeline with 5 transform steps (1MB)

💻 Local Development

World	Framework	Workflow Time	TTFB	Slurp	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	1.504s (+138.7% 🔺)	2.005s (+99.2% 🔺)	0.004s (+2.7%)	2.025s (+98.0% 🔺)	0.521s	30	1.00x
💻 Local	Nitro	1.551s (+84.9% 🔺)	2.012s (+98.8% 🔺)	0.011s (+15.3% 🔺)	2.025s (+81.4% 🔺)	0.474s	30	1.03x
🐘 Postgres	Nitro	1.552s (+148.6% 🔺)	2.005s (+99.2% 🔺)	0.004s (-6.5% 🟢)	2.026s (+98.2% 🔺)	0.474s	30	1.03x
🐘 Postgres	Next.js (Turbopack)	1.654s	2.011s	0.004s	2.026s	0.372s	30	1.10x
💻 Local	Next.js (Turbopack)	1.857s	2.009s	0.011s	2.202s	0.345s	28	1.24x
💻 Local	Express	1.937s (+155.9% 🔺)	2.011s (+95.4% 🔺)	0.009s (-4.0%)	2.423s (+133.0% 🔺)	0.486s	25	1.29x

▲ Production (Vercel)

World	Framework	Workflow Time	TTFB	Slurp	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	6.208s (-63.3% 🟢)	7.333s (-59.8% 🟢)	0.361s (+70.7% 🔺)	8.186s (-56.8% 🟢)	1.978s	8	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-	-

🔍 Observability: Next.js (Turbopack)

10 parallel streams (1MB each)

💻 Local Development

World	Framework	Workflow Time	TTFB	Slurp	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Express	0.627s (-34.8% 🟢)	1.012s (-20.8% 🟢)	0.000s (-20.7% 🟢)	1.040s (-20.4% 🟢)	0.413s	58	1.00x
🐘 Postgres	Nitro	0.662s (-31.7% 🟢)	1.014s (-18.8% 🟢)	0.000s (-100.0% 🟢)	1.023s (-18.6% 🟢)	0.361s	59	1.06x
🐘 Postgres	Next.js (Turbopack)	0.757s	1.053s	0.000s	1.060s	0.304s	57	1.21x
💻 Local	Express	1.350s (+10.2% 🔺)	2.015s (~)	0.000s (~)	2.018s (~)	0.668s	30	2.15x
💻 Local	Nitro	1.372s (+12.2% 🔺)	2.015s (~)	0.000s (+100.0% 🔺)	2.017s (~)	0.644s	30	2.19x
💻 Local	Next.js (Turbopack)	1.427s	2.014s	0.000s	2.017s	0.590s	30	2.28x

▲ Production (Vercel)

World	Framework	Workflow Time	TTFB	Slurp	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	3.573s (-64.9% 🟢)	5.382s (-53.3% 🟢)	0.000s (+Infinity% 🔺)	5.845s (-51.5% 🟢)	2.272s	11	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-	-

🔍 Observability: Next.js (Turbopack)

fan-out fan-in 10 streams (1MB each)

💻 Local Development

World	Framework	Workflow Time	TTFB	Slurp	Wall Time	Overhead	Samples	vs Fastest
🐘 Postgres	🥇 Nitro	1.316s (-26.6% 🟢)	2.066s (-3.5%)	0.000s (-3.4%)	2.086s (-4.1%)	0.770s	29	1.00x
🐘 Postgres	Express	1.324s (-25.3% 🟢)	1.996s (-8.4% 🟢)	0.000s (+Infinity% 🔺)	2.037s (-7.4% 🟢)	0.713s	30	1.01x
🐘 Postgres	Next.js (Turbopack)	1.543s	2.070s	0.000s	2.092s	0.548s	29	1.17x
💻 Local	Next.js (Turbopack)	2.775s	3.284s	0.001s	3.296s	0.521s	19	2.11x
💻 Local	Express	3.131s (-9.7% 🟢)	4.024s (~)	0.001s (-8.3% 🟢)	4.030s (~)	0.899s	15	2.38x
💻 Local	Nitro	3.140s (-7.3% 🟢)	3.907s (-3.1%)	0.001s (+110.9% 🔺)	3.910s (-3.1%)	0.771s	16	2.39x

▲ Production (Vercel)

World	Framework	Workflow Time	TTFB	Slurp	Wall Time	Overhead	Samples	vs Fastest
▲ Vercel	🥇 Next.js (Turbopack)	5.723s (+1.9%)	7.845s (+12.4% 🔺)	0.000s (-100.0% 🟢)	8.348s (+10.7% 🔺)	2.626s	8	1.00x
▲ Vercel	Express	⚠️ missing	-	-	-	-	-
▲ Vercel	Nitro	⚠️ missing	-	-	-	-	-

🔍 Observability: Next.js (Turbopack)

Summary

Fastest Framework by World

Winner determined by most benchmark wins

World	🥇 Fastest Framework	Wins
💻 Local	Nitro	11/21
🐘 Postgres	Express	16/21
▲ Vercel	Next.js (Turbopack)	21/21

Fastest World by Framework

Winner determined by most benchmark wins

Framework	🥇 Fastest World	Wins
Express	🐘 Postgres	18/21
Next.js (Turbopack)	🐘 Postgres	17/21
Nitro	🐘 Postgres	15/21

Column Definitions

Workflow Time: Runtime reported by workflow (completedAt - createdAt) - primary metric
TTFB: Time to First Byte - time from workflow start until first stream byte received (stream benchmarks only)
Slurp: Time from first byte to complete stream consumption (stream benchmarks only)
Wall Time: Total testbench time (trigger workflow + poll for result)
Overhead: Testbench overhead (Wall Time - Workflow Time)
Samples: Number of benchmark iterations run
vs Fastest: How much slower compared to the fastest configuration for this benchmark

Worlds:

💻 Local: In-memory filesystem world (local development)
🐘 Postgres: PostgreSQL database world (local development)
▲ Vercel: Vercel production/preview deployment
🌐 Turso: Community world (local development)
🌐 MongoDB: Community world (local development)
🌐 Redis: Community world (local development)
🌐 Jazz: Community world (local development)
🌐 Redis: Community world (local development)
🌐 Redis + BullMQ: Community world (local development)
🌐 Cloudflare: Community world (local development)
🌐 MySQL: Community world (local development)
🌐 Azure: Community world (local development)
🌐 NATS JetStream: Community world (local development)
🌐 Upstash: Community world (local development)

📋 View full workflow run

❌ Some benchmark jobs failed:

Local: success
Postgres: success
Vercel: failure

Check the workflow run for details.

resumable-streams.mdx (both v4 and v5) now only flags the gotcha briefly and links to the WorkflowChatTransport API reference, which carries the full explanation and a server-rewind example. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Signed-off-by: Peter Wielander <mittgfu@gmail.com>

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VaguelySerious commented May 22, 2026

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Comment thread .changeset/orphan-ui-chunks-on-resume.md Outdated

Apply suggestion from @VaguelySerious

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Signed-off-by: Peter Wielander <mittgfu@gmail.com>

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Merge branch 'main' into peter/issue-1835-client-orphan-filter

3bdac11

This was referenced May 22, 2026

Delay when resuming a chat. #1820

Open

Negative initialStartIndex can resume in the middle of a UI chunk sequence and break AI SDK chat state #1835

Open

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VaguelySerious marked this pull request as ready for review May 22, 2026 12:21

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VaguelySerious mentioned this pull request May 22, 2026

fix(workflow): drop orphan UI chunks after non-zero startIndex reconnect vercel/ai#15543

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🧪 E2E Test Results

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📊 Benchmark Results

💻 Local Development

▲ Production (Vercel)

💻 Local Development

▲ Production (Vercel)

💻 Local Development

▲ Production (Vercel)

💻 Local Development

▲ Production (Vercel)

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▲ Production (Vercel)

💻 Local Development

▲ Production (Vercel)

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▲ Production (Vercel)

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▲ Production (Vercel)

💻 Local Development

▲ Production (Vercel)

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▲ Production (Vercel)

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▲ Production (Vercel)

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▲ Production (Vercel)

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▲ Production (Vercel)

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▲ Production (Vercel)

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▲ Production (Vercel)

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▲ Production (Vercel)

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▲ Production (Vercel)

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▲ Production (Vercel)

💻 Local Development

▲ Production (Vercel)

💻 Local Development

▲ Production (Vercel)

💻 Local Development

▲ Production (Vercel)

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