test(doctor): pin the half-built-index diagnostic, which nothing asserted

[kevintseng]

Summary

vector-generation.open — the memesh doctor row that tells a user an interrupted rebuild is holding a second, full-size copy of their vectors on disk — shipped with the generation-swap work and had no test asserting it. The three test files that mention vector_generation seed that metadata key as a fixture for other behaviour, and cli-reindex-vectors-guard.test.ts covers reindex --discard-generation: the action, not the diagnostic that names it. This adds the missing read-side pin. No production code changes.

Type of change

• Feature (feat)
• Bug fix (fix)
• Refactor (refactor)
• Docs only (docs)
• Test only (test)
• Build / CI / chore
• Release (release)

Docs synced (project doc-sync rule — CLAUDE.md)

• CHANGELOG.md updated — deliberately not: no user-visible behaviour changes. CONTRIBUTING.md ties doc updates to behaviour / API / architecture changes; this is none of them.
• docs/ARCHITECTURE.md — no module structure change
• docs/api/API_REFERENCE.md — no MCP / HTTP / CLI surface change
• README.md — no user-facing change
• README locales — README.md unchanged
• Version files — no version bump
• dist/skills-manifest.json — nothing under .claude-plugin/, scripts/hooks/, skills/ or version files was touched
• memesh doctor Overall — not run; nothing in this PR can move it, and reporting a check I did not run is what this repository's rules forbid

Verification

Run in this checkout, this session:

npm run typecheck                     exit=0
node scripts/run-tests-isolated.mjs   158 files, 2314 tests passed, exit=0
npm run verify:release                exit=0
npx vitest run tests/cli/doctor-half-built-index.test.ts   5 passed, exit=0

• npx tsc --noEmit clean (via npm run typecheck, which covers src/, tests/ and the root configs)
• npm run build — not run; no source file changed, so dist/ is unchanged
• npm test -- --run passing — run as scripts/run-tests-isolated.mjs (throwaway HOME): 158 files, 2314 tests, 0 failed. The five new cases are this file's; I did not re-run the suite on main to state a delta, so none is claimed.
• Hooks untouched
• LLM flows untouched

Break-test. A green suite is not evidence a guard is protected, so the check was mutated in a copy of the tree, rebuilding dist each time — the tests spawn the built CLI, so a mutation left in src alone grades a binary that never changed:

mutant	result
readVectorGeneration() short-circuited to { state: 'none' }	KILLED (4 cases red)
const staged = generationRowIds().size → = 0	KILLED (1 case red)
severity 'warn' → 'pass'	KILLED (2 cases red)
state === 'open' inverted	INVALID, not counted — stops type-checking, so it was never executed

Restored copy green again (exit=0). Restoration is by writing the original file back, never git checkout.

Test plan

• npx vitest run tests/cli/doctor-half-built-index.test.ts — 5 passed
• Delete the vector_generation branch in src/core/doctor.ts (or set staged to a constant), npx tsc, re-run the file — it must go red
• npm run verify:release — exit=0, C1: new=0

Known limitations / follow-ups

• The fixture writes the staging table directly instead of killing a real rebuild mid-flight. A real rebuild needs an embedding provider, and what doctor reads is the state, not the route to it.
• This closes the last of the four items the PR feat: reindex builds the new vector index beside the old one (generation swap) #185 review deferred. The other three were already implemented and pinned — already_staged / stale-hash resume (reindex-reports-what-happened.test.ts:403,438), the reindex circuit breaker (:464), and the body-phase timeout (embedder-provider-fetch.test.ts:152). Verified by reading the assertions, not by the presence of a file name.