test: add concurrent resolveSnapshot race test (API-AI-R01)

- Simulates two concurrent getSnapshot calls with no valid snapshot
- Documents the known race: both trigger buildSnapshot, second update overwrites first
- Verifies both calls complete without error (accepted-risk behavior)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/modules/ai-runtime/internal/runtime-internal.service.spec.ts

@@ -329,6 +329,38 @@ describe('RuntimeInternalService', () => {
     });
   });
 
+  // ═══════════════════════════════════════════════════════════════════
+  // resolveSnapshot: concurrent race (API-AI-R01)
+  // ═══════════════════════════════════════════════════════════════════
+
+  describe('resolveSnapshot concurrent race', () => {
+    it('handles concurrent getSnapshot without error (known race, accepted risk)', async () => {
+      // Simulate: two calls with no valid snapshot → both trigger buildSnapshot
+      const job = { id: 'j1', userId: 'u1', targetType: 'material', targetId: 'm1', snapshotId: null };
+      mockAiRuntimeJob.findUnique.mockResolvedValue(job);
+
+      // Each buildSnapshot call returns a new id (simulating two builds)
+      mockSnapshotBuilder.buildSnapshot
+        .mockResolvedValueOnce({ ...mockSnapshot, id: 'snap-A' })
+        .mockResolvedValueOnce({ ...mockSnapshot, id: 'snap-B' });
+      // First update writes snap-A, second overwrites with snap-B (the race)
+      mockAiRuntimeJob.update.mockResolvedValue({});
+
+      const [r1, r2] = await Promise.all([
+        service.getSnapshot('j1'),
+        service.getSnapshot('j1'),
+      ]);
+
+      // Both calls succeed; one snapshot may be orphaned (documented risk)
+      expect(r1.snapshotId).toBeDefined();
+      expect(r2.snapshotId).toBeDefined();
+      // Two buildSnapshot calls issued (the race)
+      expect(mockSnapshotBuilder.buildSnapshot).toHaveBeenCalledTimes(2);
+      // Job updated twice (second overwrites first — orphan snap-A)
+      expect(mockAiRuntimeJob.update).toHaveBeenCalledTimes(2);
+    });
+  });
+
   // ═══════════════════════════════════════════════════════════════════
   // resolveCredential
   // ═══════════════════════════════════════════════════════════════════