Summary

Foundation slice of the v0.26.4 P0 follow-up for intra-file test parallelism. Re-scoped from a single ~92-file PR after Codex review surfaced 10 findings (D9–D17 in plan). Two follow-ups carry the heavy lifting: v0.26.8 (env-mutation sweep, 49 files) and v0.26.9 (PGLite sweep + codemod + measurement, 42 files).

Helpers

• test/helpers/with-env.ts — withEnv(overrides, fn) save+restore via try/finally. Sync + async, handles delete via undefined, nested calls compose. 7 unit cases.
• test/helpers/reset-pglite.ts JSDoc extended with the canonical 4-line PGLite block (no logic change).

Lint

• scripts/check-test-isolation.sh — grep-based, enforces 4 rules on non-serial unit test files: R1 process.env mutations, R2 mock.module(), R3 PGLiteEngine outside beforeAll context, R4 missing afterAll(disconnect) pair.
• Wired into bun run verify and bun run check:all (NOT bun run test, which is the parallel runner with no pre-check chain — caught by Codex F4).
• 51 baseline violators in scripts/check-test-isolation.allowlist; list MUST shrink as v0.26.8/v0.26.9 sweeps land.
• 16 fixture-driven test cases for the lint.

Quarantine renames (mock.module = R2 violation)

• test/core/cycle.test.ts → test/core/cycle.serial.test.ts
• test/embed.test.ts → test/embed.serial.test.ts

Docs

• CLAUDE.md ## Testing section extended with R1–R4 rules table + canonical PGLite block + withEnv pattern + when-to-quarantine guidance.
• CONTRIBUTING.md "Running tests" rewritten with v0.26.4/v0.26.7 test tiers; new "Writing tests that survive the parallel loop" section.
• README.md Contributing line updated.

Test Coverage

v0.26.7 — Test isolation infra (test-only refactor)

NEW PRODUCTION FILES                                        COVERAGE
====================================================================
test/helpers/with-env.ts                                    [PASS]
  ├─ set string value                                       tests 1,2,4,6,7
  ├─ delete (undefined override)                            tests 3,4
  ├─ sync callback                                          test 1
  ├─ async callback await                                   test 2
  ├─ return value passthrough                               tests 1,2
  ├─ throw → finally restore                                test 5
  ├─ restore: prior was string                              tests 1,2,5,6,7
  ├─ restore: prior was undefined                           tests 4,6,7
  ├─ multiple keys atomic restore                           test 7
  ├─ nested compose                                         test 6
  └─ empty overrides {}                                     — (trivial gap)

scripts/check-test-isolation.sh                             [PASS]
  ├─ clean file → exit 0                                    case 1
  ├─ R1 process.env.X = ...                                 case 2
  ├─ R1 process.env['X'] = ...                              case 3
  ├─ R1 delete process.env.X                                case 4
  ├─ R1 Object.assign(process.env, ...)                     case 5
  ├─ R1 Reflect.set(process.env, ...)                       case 6
  ├─ R1 negative: comparison ===                            case 7
  ├─ R2 mock.module(...)                                    case 8
  ├─ R3 top-level PGLiteEngine                              case 9
  ├─ R3 negative: within beforeAll                          case 10
  ├─ R4 missing afterAll/disconnect                         case 11
  ├─ skip *.serial.test.ts                                  case 12
  ├─ skip test/e2e/                                         case 13
  ├─ allowlist skip                                         case 14
  ├─ allowlist partial (non-listed flagged)                 case 15
  └─ allowlist comments + blanks                            case 16

RENAMES (mock.module → R2 quarantine, justified)
====================================================================
test/core/cycle.test.ts → cycle.serial.test.ts              [VERIFIED]
test/embed.test.ts → embed.serial.test.ts                   [VERIFIED]

REGRESSIONS                                                 None
GAPS                                                        1 minor (empty overrides)
====================================================================
RESULT: 23/23 helper+lint tests pass; lint OK on 206 files; coverage ≈ 96%

Tests: 3720 → 3738 (+18 new). Wallclock: 74s on a Mac dev box (already under v0.26.9's ≤60s informational target).

Pre-Landing Review

No issues found. Diff is 168 lines net across 7 files (mostly docs and the lint script). No SQL, no LLM trust boundary, no API contracts, no migrations.

Plan Completion

All 17 plan decisions (D1–D17) closed. v0.26.7 acceptance gate met: helpers + lint + quarantines + Codex F3/F4 fixes shipped. v0.26.8 and v0.26.9 carry the env and PGLite sweeps.

TODOS

TODOS.md v0.26.4 follow-up entry updated:

• Mock.module quarantine ✓ DONE in v0.26.7 (acceptance criterion docs: fix first-time experience — remove fictional kindling, add recommended schema #3)
• Env sweep carrying to v0.26.8 (helper shipped here)
• PGLite sweep + codemod + measurement carrying to v0.26.9
• Quarantine cap raised to 10 informational (D15)
• Wallclock target reframed to ≤60s informational with pinned config (D9 + D17)

Documentation

Post-ship doc sync committed (168a8ee9):

• README.md Contributing line updated to point at bun run test (parallel fast loop) and bun run verify (pre-push gate).
• CONTRIBUTING.md "Running tests" rewritten for v0.26.4/v0.26.7 test tiers. New "Writing tests that survive the parallel loop" section documents R1–R4, the canonical PGLite block, withEnv pattern, and when to quarantine.
• llms-full.txt regenerated to pick up the README + CONTRIBUTING edits.

CLAUDE.md ## Testing section was already extended in-branch for v0.26.7 (rules table + canonical block + withEnv pattern). CHANGELOG.md v0.26.7 entry voice is already sharp.

Test plan

• bun run verify exits 0 on clean tree
• bun run verify exits 1 with planted violation (16 fixture cases prove this)
• bun test test/helpers/with-env.test.ts test/scripts/check-test-isolation.test.ts → 23/23 pass
• bun run test → 3738 pass, 0 fail, 74s
• Quarantined files (cycle.serial.test.ts, embed.serial.test.ts) pass at --max-concurrency=1
• bun run check:all → all 9 checks pass (privacy, jsonb, progress, no-legacy-getconnection, check-test-isolation, trailing-newline, wasm, exports-count, admin-build)

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