fix(test): isolate server unit tests from thread-pool env bleed

[garvitkaushik-123]

Summary

Fix the flaky server-unit precommit path by ensuring individual changed test files run with the same isolated server Vitest configuration as the full suite.

Root cause: the precommit script's individual-file path (planServerUnitRun → kind: 'files') invoked Vitest without --config, so it did not load the server setup and isolation settings. Full-suite runs were unaffected because npm run test:server-unit already passes the server config.

Changes

1. scripts/precommit-server-unit.cjs — pass --config server/vitest.config.ts on the individual-file path.
2. server/vitest.config.ts — explicitly declare pool: 'forks' instead of relying on the default.

Verification

• npx vitest run tests/precommit-server-unit.test.ts — 14 passed
• npm exec -- vitest run --config server/vitest.config.ts server/tests/unit/auth-api-key-format.test.ts — 5 passed

Refs #6740

[bokelley]

I pushed a maintainer follow-up that narrows this to the effective fix:

• pass --config server/vitest.config.ts for changed-file precommit runs;
• keep the server pool explicitly set to forks;
• remove the protocol changeset (this is operational test infrastructure);
• remove the root env defaults and poolMatchGlobs changes. poolMatchGlobs is not supported by the pinned Vitest 4.1.10, and global env defaults could mask test isolation bugs.

Verified with:

• npx vitest run tests/precommit-server-unit.test.ts — 14 passed
• npm exec -- vitest run --config server/vitest.config.ts server/tests/unit/auth-api-key-format.test.ts — 5 passed

[aao-secretariat]

Ladon verdict: Approve

Approve — two-file test-infra fix with no blocking findings.

What I checked:

• scripts/precommit-server-unit.cjs now passes --config server/vitest.config.ts on the individual-file path, so partial-commit server unit runs use the server config instead of falling through to the root threads pool. Correct and consistent with the full path (package.json:122 test:server-unit already used the server config).
• server/vitest.config.ts makes pool: 'forks' explicit — sound.
• No protocol surface touched (static/schemas/source/**, docs/reference/**, dist/**, task defs), so no changeset is required. Schema↔docs coherence, oneOf discriminator, artifact immutability, and 3.1.x eligibility gates are all N/A.

Medium findings: none.

Note (low, non-blocking): The PR description overclaims — items 3-4 (a root vitest.config.ts poolMatchGlobs edit, a new tests/setup/env-defaults.ts, and 1052 root tests) are referenced but not present in the diff (only 2 files changed). The actual change on disk is sound; the mismatch is a description accuracy issue, not a code defect.

No critical/high/medium findings. gated_paths is false, high_risk is false, no author-team gate. Falls through to row 9 → approve. (review_decision: REVIEW_REQUIRED only blocks approval when gated_paths is true, which it is not here.)