refactor(simplify): one source per rule, shared test helpers, a faster isolation test [skip-docs]

/simplify over a97efb6..HEAD (the plan_version 1.9 / trial-4 delivery).

- coordinator-contract: engine names come from engine-findings ENGINES;
  one markedMajorCodeReview predicate under both lowering checks;
  isEngineFinding everywhere; the unreachable branch (c) of
  illegalBriefLowering folded into (e).
- armB workflow: RULE_KEYS = Object.keys(RULE_TIERS); the engine map is a
  literal pinned equal to ENGINES by the workflow test.
- plan-schema: usesFilesGrammar() is the one 1.9 check (validator, sweep,
  testFirstFiles, stepTestsOnlyFromFields); opensEntry built on opensChunk.
- plan-validator: one issue builder for the Files and Test first grammar.
- plan-scope-sweep: the 1.9 and the 6.2.0 reader are one if/else.
- artifact-commit: TRAILER_RE/trailerProblem no longer exported (no
  importer); the order comment says the CLI finds the repo root first.
- tests: the lock drivers in session-id-isolation (d) run side by side per
  mode (~100 s -> ~30 s); a shared artifact-repo helper; severityRank and
  extractFindingsBlock reused; childEnv(env) without a spread; one copy of
  the PLAN_VERSION_CURRENT check.

Plan readers: validator errors/warnings, plannedPaths, fieldPaths,
testFirstFiles and stepTestsOnlyFromFields compared byte for byte against
HEAD over 510 plans / 1692 steps plus 210 synthetic 1.7-1.9 cases: same.
Suite 2384 (2382/0/2).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/lib/artifact-commit-trailer.test.mjs

@@ -10,46 +10,18 @@
 import { test } from 'node:test';
 import { strict as assert } from 'node:assert';
 import { spawnSync } from 'node:child_process';
-import { mkdirSync, mkdtempSync, readFileSync, readdirSync, realpathSync, rmSync, writeFileSync } from 'node:fs';
-import { tmpdir } from 'node:os';
+import { readFileSync, readdirSync, realpathSync, rmSync } from 'node:fs';
 import { dirname, join } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { childEnv } from '../helpers/child-env.mjs';
+import { artifactRepo, git } from '../helpers/artifact-repo.mjs';
 import { commitArtifacts } from '../../lib/util/artifact-commit.mjs';
 
 const HERE = dirname(fileURLToPath(import.meta.url));
 const ROOT = join(HERE, '..', '..');
 const CLI = join(ROOT, 'lib', 'util', 'artifact-commit.mjs');
-const LOG = join(ROOT, 'lib', 'util', 'approval-log.mjs');
-const H1 = 'c'.repeat(64);
 const TRAILER = 'Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>';
 
-function git(cwd, ...args) {
-  return spawnSync('git', args, { cwd, encoding: 'utf8', env: childEnv() });
-}
-
-// Same shape as the repo() factory in tests/lib/artifact-commit.test.mjs.
-function repo({ withLog = true } = {}) {
-  const d = mkdtempSync(join(tmpdir(), 'artifact-trailer-'));
-  git(d, 'init', '-q');
-  git(d, 'config', 'user.name', 'Test');
-  git(d, 'config', 'user.email', 'test@example.invalid');
-  git(d, 'config', 'commit.gpgsign', 'false');
-  mkdirSync(join(d, '.hooks-none'));
-  git(d, 'config', 'core.hooksPath', '.hooks-none');
-  writeFileSync(join(d, 'README.md'), 'x\n');
-  git(d, 'add', 'README.md');
-  git(d, 'commit', '-q', '-m', 'init');
-  const proj = join(d, '.claude', 'projects', '2026-10-12-trailer');
-  mkdirSync(proj, { recursive: true });
-  writeFileSync(join(proj, 'brief.md'), '# brief\n');
-  if (withLog) {
-    spawnSync(process.execPath, [LOG, 'append', '--kind', 'intent', '--subject', join(proj, 'brief.md'), '--sha256', H1],
-      { cwd: d, env: childEnv() });
-  }
-  return { d, brief: join(proj, 'brief.md') };
-}
-
 function run(args, cwd) {
   return spawnSync(process.execPath, [CLI, ...args], { cwd, encoding: 'utf8', env: childEnv() });
 }
@@ -57,7 +29,7 @@ function run(args, cwd) {
 const head = (d) => git(d, 'rev-parse', 'HEAD').stdout.trim();
 
 test('a passed trailer ends the commit message and git parses it as a trailer', () => {
-  const { d, brief } = repo();
+  const { d, brief } = artifactRepo({ prefix: 'artifact-trailer-', project: '2026-10-12-trailer' });
   try {
     const r = run(['--store', 'local', '--artifact', brief, '--message', 'docs(voyage): approve intent trailer',
       '--trailer', TRAILER], d);
@@ -81,7 +53,7 @@ const REFUSED = [
 
 for (const [name, value] of REFUSED) {
   test(`refused with exit 1, nothing committed: ${name}`, () => {
-    const { d, brief } = repo();
+    const { d, brief } = artifactRepo({ prefix: 'artifact-trailer-', project: '2026-10-12-trailer' });
     try {
       const before = head(d);
       const r = run(['--store', 'local', '--artifact', brief, '--message', 'x', '--trailer', value], d);
@@ -95,7 +67,7 @@ for (const [name, value] of REFUSED) {
 }
 
 test('a call without a trailer exits 1 with HEAD unchanged', () => {
-  const { d, brief } = repo();
+  const { d, brief } = artifactRepo({ prefix: 'artifact-trailer-', project: '2026-10-12-trailer' });
   try {
     const before = head(d);
     const r = run(['--store', 'local', '--artifact', brief, '--message', 'x'], d);
@@ -107,7 +79,7 @@ test('a call without a trailer exits 1 with HEAD unchanged', () => {
 });
 
 test('the trailer check comes before any git call: "nothing to commit" does not mask a missing trailer', () => {
-  const { d, brief } = repo({ withLog: false });
+  const { d, brief } = artifactRepo({ prefix: 'artifact-trailer-', project: '2026-10-12-trailer', withLog: false });
   try {
     const r = run(['--store', 'local', '--artifact', brief, '--message', 'x'], d);
     assert.equal(r.status, 1, r.stdout + r.stderr);
@@ -116,7 +88,7 @@ test('the trailer check comes before any git call: "nothing to commit" does not
 });
 
 test('commitArtifacts takes the trailer too, and refuses without it', () => {
-  const { d, brief } = repo();
+  const { d, brief } = artifactRepo({ prefix: 'artifact-trailer-', project: '2026-10-12-trailer' });
   try {
     const repoDir = realpathSync(d);
     const before = head(d);
@@ -132,7 +104,7 @@ test('commitArtifacts takes the trailer too, and refuses without it', () => {
 });
 
 test('usage before trailer: a missing --store is still exit 2, with or without a trailer', () => {
-  const { d, brief } = repo();
+  const { d, brief } = artifactRepo({ prefix: 'artifact-trailer-', project: '2026-10-12-trailer' });
   try {
     assert.equal(run(['--artifact', brief, '--message', 'x'], d).status, 2);
     assert.equal(run(['--artifact', brief, '--message', 'x', '--trailer', TRAILER], d).status, 2);