Git Integration fails after build, looking for routes manifest in repo root

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I’m seeing a reproducible Git Integration finalization failure across 4 Vercel projects and a fresh sandbox project. The app builds successfully and prebuilt deployment works, but Git Integration fails after Build Completed in /vercel/output with:
ENOENT: no such file or directory, lstat ‘/vercel/path0/.next/routes-manifest-deterministic.json’ and understand the problem!

Current behavior:

Git Integration clones/builds the repo.
Vercel detects Next.js 16.2.3.
Install succeeds.
npm run build succeeds.
Logs show Build Completed in /vercel/output.
Deployment then fails during finalization/onBuildComplete.
The final error looks for the manifest at:
/vercel/path0/.next/routes-manifest-deterministic.json
Expected behavior:
Since the Vercel project Root Directory is configured as rtlab_dashboard, Git Integration should either:
use the configured Root Directory output, or
use the completed Build Output at /vercel/output.
It should not finalize by looking for .next in the repository root.

Repository:
cabaniasriocuarto/Bot-Trading-IA
Project/app:
RTLAB Strategy Console / Next.js dashboard
Root Directory configured in Vercel:
rtlab_dashboard
Commit:
322aa8b7f5f683181e572c441c47b4129d3bcc88
Detected Next.js version in Vercel logs:
16.2.3
The dashboard build script is:
next build --webpack
Validation on main:
npm ci: PASS, 0 vulnerabilities
npm audit --audit-level=moderate: PASS, 0 vulnerabilities
npm run lint: PASS
npm run typecheck: PASS
npm run build: PASS
npm run test:smoke:live-console: PASS
Failing Git Integration deployments:
bot-trading-ia: dpl_9e1EGV5Wk8JJYihL8HjYc7Y947Wf
bot-trading-ia-2: dpl_Fv1XsruTVUSixVtDnBjBgFjbrSFr
bot-trading-ia-csud: dpl_9T3hEyP26yo2P3zPhk5VNqC2P74V
bot-trading-ia-staging-2: dpl_Evydroq6zJH26XakvjuHios8Y4QQ
Fresh sandbox project created to rule out stale project metadata/cache:
Project: bot-trading-ia-rtlops106-sandbox
Repo: github:cabaniasriocuarto/Bot-Trading-IA
Root Directory: rtlab_dashboard
Framework: Next.js
Output Directory: default/null
Node: 24.x initially
Sandbox deployment also failed with the same error:
dpl_2BZGzgSKLmpTXVTfudBAS6Lj71Uu
Sandbox redeploy without build cache also failed with the same error:
dpl_HnDqhRVd5Pm6nCfqSCJJBsS2fJms
Logs showed:
Skipping build cache, deployment was triggered without cache
Detected Next.js version: 16.2.3
Build Completed in /vercel/output
ENOENT: no such file or directory, lstat ‘/vercel/path0/.next/routes-manifest-deterministic.json’
Sandbox with Node 22.x also failed with the same error:
dpl_FtNmyHTEC7rmarVnESBZhmiMJZ3L

Checklist already reviewedWe reviewed the common routes-manifest causes:Build Command: OK. It calls next build --webpack.Output Directory: OK. No override; default/null with framework nextjs.Build failure / OOM: Not seen. Logs show compilation, TypeScript, page generation, traces, and Build Completed in /vercel/output.Turborepo/NX: Not applicable. No turbo.json or nx.json.Custom distDir: Not applicable. next.config.ts does not define distDir.next export: Not used.Sentry/source maps: Not used.Errors before manifest: none found, only a non-fatal .env warning.Important comparison: prebuilt deployment worksThe same app/code path deploys successfully using Vercel prebuilt deployment:vercel build
vercel deploy --prebuilt --archive=tgz --target=previewReady prebuilt deployment:dpl_CQC5fTLEcd8965NpoE7xi9Y5ABRM
https://bot-trading-dx9ujndv1-ranquel-tech-lab.vercel.appThat workflow passed:npm ci
npm audit
npm run lint
npm run typecheck
npm run build
npm run test:smoke:live-console
vercel build
vercel deploy --prebuilt
vercel inspectQuestionWhy is Vercel Git Integration finalization looking for:/vercel/path0/.next/routes-manifest-deterministic.jsoninstead of using the configured Root Directory:rtlab_dashboardor the completed Build Output:/vercel/outputIs there a known issue with Next.js 16.2.3 + monorepo Root Directory + Git Integration finalization?Is there a recommended workaround other than using prebuilt deployments?