feat(sdk): missing phase dir surfaces NO_PHASE_DIR reason (#3184)

Cycle 3 of ~15: when resolvePhaseDir returns null, predicate
returns a typed NO_PHASE_DIR reason. Previously the empty
reasons array was indistinguishable from other failure modes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

sdk/src/query/phase-uat-passed.test.ts

@@ -43,6 +43,24 @@ describe('isPhaseUatPassed', () => {
     expect(result.reasons.length).toBe(0);
   });
 
+  it('returns passed=false with NO_PHASE_DIR reason when phase has no directory', async () => {
+    const localTmp = await mkdtemp(join(tmpdir(), 'gsd-uat-c3-'));
+    try {
+      const otherPhaseDir = join(localTmp, '.planning', 'phases', '06-other');
+      await mkdir(otherPhaseDir, { recursive: true });
+      await writeFile(join(otherPhaseDir, '06-HUMAN-UAT.md'), UAT_PASS_CONTENT);
+
+      // Query phase 5 which has NO directory in this fixture
+      const result = await isPhaseUatPassed(localTmp, '5');
+      expect(result.passed).toBe(false);
+      expect(result.items.length).toBe(0);
+      expect(result.reasons.length).toBe(1);
+      expect(result.reasons[0].code).toBe(REASON_CODE.NO_PHASE_DIR);
+    } finally {
+      await rm(localTmp, { recursive: true, force: true });
+    }
+  });
+
   it('returns passed=false with NON_PASS_RESULT reason when single UAT item has result: issue', async () => {
     const nonPassContent = `---
 status: complete

sdk/src/query/phase-uat-passed.ts

@@ -11,6 +11,7 @@ import { resolvePhaseDir } from './phase-list-queries.js';
 
 export const REASON_CODE = Object.freeze({
   NON_PASS_RESULT: 'non_pass_result',
+  NO_PHASE_DIR: 'no_phase_dir',
 } as const);
 
 export type ReasonCode = typeof REASON_CODE[keyof typeof REASON_CODE];
@@ -62,7 +63,12 @@ export async function isPhaseUatPassed(
 }> {
   const dir = await resolvePhaseDir(phase, projectDir, workstream);
   if (!dir) {
-    return { passed: false, reasons: [], reasonsHuman: [], items: [] };
+    return {
+      passed: false,
+      reasons: [{ code: REASON_CODE.NO_PHASE_DIR }],
+      reasonsHuman: [],
+      items: [],
+    };
   }
 
   const files = await readdir(dir);