test: reuse serial Vitest worker

[mohanagy]

Summary

• keep serial test files inside one isolated Vitest fork instead of cold-forking once per file
• preserve real MCP subprocess coverage and every existing startup/shutdown budget
• add retained fixture-entry, MCP-initialized, sanitized health, and original-cause diagnostics to the exact recurring restart boundary
• lock the runner behavior with a focused repository contract

Root cause

fileParallelism: false serialized 108 files but Vitest still replaced the fork worker between files. Process-backed tests therefore cold-started their real MCP Node child while the suite was also repeatedly cold-starting its outer worker. Under aggregate load this intermittently delayed an inner fixture past the existing 1s/5s integration budgets; the failure migrated between files and every exact case passed immediately in isolation.

A control run with only poolOptions.forks.singleFork kept one worker PID for the full suite and passed. The committed configuration also keeps isolate: true, so module isolation remains enabled.

TDD evidence

• reproduced unchanged on supported Node 22.22.3: 1 failure after 1,248 passes in the failed-restart replacement startup case
• exact failing case passed focused in 297 ms
• added the runner contract and observed it fail because singleFork was absent
• implemented the smallest config change and observed the focused contract pass

Security impact

• test-runner configuration only; no production runtime, public API, package, secret-store, or network behavior changes
• per-file module isolation remains explicitly enabled
• real MCP subprocesses, shutdown/startup budgets, process containment, assertions, and coverage thresholds remain unchanged
• failure diagnostics contain only allowlisted lifecycle state and preserve the original test error as cause; they do not include environment values, tokens, credentials, or raw provider output

Validation

• npm test: 1,250 passed, 24 platform-skipped
• npm run test:core: 404 passed, 24 platform-skipped
• npm run test:coverage: 1,250 passed, 24 platform-skipped; 95.39% statements, 91.85% branches
• npm run lint
• npm run typecheck
• npm run build
• npm run smoke:cli
• npm run check:pack: 45 files verified
• npm run test:package: 20 passed

No timeout, skip, assertion, coverage threshold, production lifecycle behavior, or process containment was changed.

Closes #122

[coderabbitai]

📝 Walkthrough

Walkthrough

Vitest now reuses a single isolated fork for serial process-backed tests. The upstream restart teardown test adds startup markers, waits for initialization state, reports structured restart diagnostics, and removes its temporary directory during cleanup.

Changes

Test reliability

Layer / File(s)	Summary
Vitest fork isolation contract vitest.config.ts, tests/release-config.test.ts	Serial tests reuse one isolated fork, and a contract test verifies the required concurrency and isolation settings.
Restart teardown diagnostics tests/upstream-manager.test.ts	The restart test tracks startup and initialization markers, reports structured error and health data on failure, and cleans up its temporary directory.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• mohanagy/miftah#51: Related upstream manager restart lifecycle testing.
• mohanagy/miftah#152: Adds filesystem markers and diagnostics for upstream restart behavior.
• mohanagy/miftah#175: Adds restart sentinel tracking and health diagnostics.

Poem

A bunny watched one fork stay near,
While restart markers made things clear.
Health states hopped into a chart,
Temp files vanished—clean and smart.
Tests now thump their paws: “Success!”

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes address #122 by reusing one serial Vitest fork and preserving process coverage, budgets, and lifecycle assertions.
Out of Scope Changes check	✅ Passed	No clear out-of-scope changes were introduced; the edits stay within the test and configuration contract.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title clearly and concisely describes the main change: reusing the serial Vitest worker.
Description check	✅ Passed	The description covers the required Summary, Security impact, and Validation sections with relevant details and results.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/122-lifecycle-root-cause

---

_{Comment @coderabbitai help to get the list of available commands.}