fix(frontend): preserve generated app entrypoint

[mira-2026]

Summary

• resolve the single generated JavaScript output that owns src/main.tsx
• repair Bun's generated module-script target when HTML-entry builds with splitting and metafile output point at an unrelated shared chunk
• fail closed on ambiguous app outputs or module scripts, and measure the initial bundle from the real application graph

Production incident

The deployment of PR #344 (195e665d) passed service health checks but served an empty #root. Its generated index.html loaded a 1.7 kB shared Switch chunk instead of the application bootstrap. Production was rolled back successfully to 96f613d2 before this hotfix.

Verification

• bun run lint:frontend
• bun test src/test/frontendBuildArtifacts.test.ts — 6 passed
• bun test — 499 passed
• bun run build:frontend
• bun run build:backend
• bun run release:manifest — 236 artifacts, both component identities on 2347976e
• clean-build browser smoke rendered the login page with no console errors

Docs: not needed — this is an internal build-output correctness fix with no configuration, API, or operator-contract change.

[coderabbitai]

📝 Walkthrough

Walkthrough

The frontend build now resolves the JavaScript output for src/main.tsx, rewrites generated index.html to reference that output, and seeds initial bundle measurement from the application output. Tests update build metadata fixtures and cover HTML repair.

Changes

Frontend app entrypoint

Layer / File(s)	Summary
Application output resolution and HTML repair scripts/frontendBuildArtifacts.ts, src/test/frontendBuildArtifacts.test.ts	Adds application-output discovery, module-script validation, HTML rewriting, and coverage for repairing an unrelated script target.
Build pipeline entrypoint emission scripts/frontendBuild.ts	Invokes writeFrontendHtmlAppEntrypoint after the build metafile is available.
Initial bundle graph seeding scripts/frontendBuildArtifacts.ts, src/test/frontendBuildArtifacts.test.ts	Seeds initial output traversal from the src/main.tsx output and updates related metadata fixtures and expectations.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant FrontendBuild
  participant Bun
  participant FrontendBuildArtifacts
  participant IndexHtml
  FrontendBuild->>Bun: build frontend and produce metafile
  Bun-->>FrontendBuild: return metafile
  FrontendBuild->>FrontendBuildArtifacts: writeFrontendHtmlAppEntrypoint(metafile, outdir)
  FrontendBuildArtifacts->>FrontendBuildArtifacts: resolve src/main.tsx output
  FrontendBuildArtifacts->>IndexHtml: rewrite module script src
  IndexHtml-->>FrontendBuildArtifacts: persist application bundle path

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Possibly related PRs

• rajohan/Mira-Dashboard#344: Extends the frontend bundle measurement and budget tooling in the same module.

Suggested labels: type: tests

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title is concise and accurately summarizes the frontend entrypoint fix.
Description check	✅ Passed	It covers the summary, incident context, and verification, but omits several template sections like risk checklist and deployment notes.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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