fix(state): scope phase counting to current milestone

Extract getMilestonePhaseFilter() from milestone.cjs closure into core.cjs
as a shared helper. Apply it in buildStateFrontmatter and cmdPhaseComplete
so multi-milestone projects count only current milestone's phases instead
of all directories on disk.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/core.test.cjs

@@ -22,6 +22,7 @@ const {
   safeReadFile,
   pathExistsInternal,
   getMilestoneInfo,
+  getMilestonePhaseFilter,
   getRoadmapPhaseInternal,
   searchPhaseInDir,
   findPhaseInternal,
@@ -665,3 +666,113 @@ describe('getRoadmapPhaseInternal', () => {
     assert.ok(!result.section.includes('Phase 2: API'));
   });
 });
+
+// ─── getMilestonePhaseFilter ────────────────────────────────────────────────────
+
+describe('getMilestonePhaseFilter', () => {
+  let tmpDir;
+
+  beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'gsd-core-test-'));
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases'), { recursive: true });
+  });
+
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  test('filters directories to only current milestone phases', () => {
+    // ROADMAP lists only phases 5-7
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'ROADMAP.md'),
+      [
+        '## Roadmap v2.0: Next Release',
+        '',
+        '### Phase 5: Auth',
+        '**Goal:** Add authentication',
+        '',
+        '### Phase 6: Dashboard',
+        '**Goal:** Build dashboard',
+        '',
+        '### Phase 7: Polish',
+        '**Goal:** Final polish',
+      ].join('\n')
+    );
+
+    // Create phase dirs 1-7 on disk (leftover from previous milestones)
+    for (let i = 1; i <= 7; i++) {
+      const padded = String(i).padStart(2, '0');
+      fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', `${padded}-phase-${i}`));
+    }
+
+    const filter = getMilestonePhaseFilter(tmpDir);
+
+    // Only phases 5, 6, 7 should match
+    assert.strictEqual(filter('05-auth'), true);
+    assert.strictEqual(filter('06-dashboard'), true);
+    assert.strictEqual(filter('07-polish'), true);
+
+    // Phases 1-4 should NOT match
+    assert.strictEqual(filter('01-phase-1'), false);
+    assert.strictEqual(filter('02-phase-2'), false);
+    assert.strictEqual(filter('03-phase-3'), false);
+    assert.strictEqual(filter('04-phase-4'), false);
+  });
+
+  test('returns pass-all filter when ROADMAP.md is missing', () => {
+    const filter = getMilestonePhaseFilter(tmpDir);
+
+    assert.strictEqual(filter('01-foundation'), true);
+    assert.strictEqual(filter('99-anything'), true);
+  });
+
+  test('returns pass-all filter when ROADMAP has no phase headings', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'ROADMAP.md'),
+      '# Roadmap\n\nSome content without phases.\n'
+    );
+
+    const filter = getMilestonePhaseFilter(tmpDir);
+
+    assert.strictEqual(filter('01-foundation'), true);
+    assert.strictEqual(filter('05-api'), true);
+  });
+
+  test('handles letter-suffix phases (e.g. 3A)', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'ROADMAP.md'),
+      '### Phase 3A: Sub-feature\n**Goal:** Sub work\n'
+    );
+
+    const filter = getMilestonePhaseFilter(tmpDir);
+
+    assert.strictEqual(filter('03A-sub-feature'), true);
+    assert.strictEqual(filter('03-main'), false);
+    assert.strictEqual(filter('04-other'), false);
+  });
+
+  test('handles decimal phases (e.g. 5.1)', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'ROADMAP.md'),
+      '### Phase 5: Main\n**Goal:** Main work\n\n### Phase 5.1: Patch\n**Goal:** Patch work\n'
+    );
+
+    const filter = getMilestonePhaseFilter(tmpDir);
+
+    assert.strictEqual(filter('05-main'), true);
+    assert.strictEqual(filter('05.1-patch'), true);
+    assert.strictEqual(filter('04-other'), false);
+  });
+
+  test('returns false for non-phase directory names', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'ROADMAP.md'),
+      '### Phase 1: Init\n**Goal:** Start\n'
+    );
+
+    const filter = getMilestonePhaseFilter(tmpDir);
+
+    assert.strictEqual(filter('not-a-phase'), false);
+    assert.strictEqual(filter('.gitkeep'), false);
+  });
+});