fix(library): stop genre-tags migration gate flashing on every launch (#1061)

runGenreTagsPhase entered the blocking 'inspecting' phase before awaiting
the inspect IPC, so the migration modal briefly appeared on every startup
once the one-time genre backfill was already complete. Inspect first without
a blocking phase and only switch to 'running' when work is actually needed.

src/hooks/useMigrationOrchestrator.test.ts

@@ -129,6 +129,40 @@ describe('useMigrationOrchestrator', () => {
     expect(rewriteFrontendStoreKeysMock).not.toHaveBeenCalled();
   });
 
+  it('keeps startup non-blocking while genre-tags inspect is pending (no gate flash)', async () => {
+    localStorage.setItem(DONE_FLAG, '1');
+    migrationInspectMock.mockResolvedValue({
+      needsMigration: false,
+      hasSkippedUnknownServerRows: false,
+      canRun: true,
+      warnings: [],
+      unmappedEmptyBucket: false,
+      library: { totalLegacyRows: 0, skippedUnknownServerRows: 0, tables: {} },
+      analysis: { totalLegacyRows: 0, skippedUnknownServerRows: 0, tables: {} },
+      mappings: [{ legacyId: 'legacy-a', indexKey: 'a.test' }],
+    });
+    let resolveGenre: ((value: any) => void) | undefined;
+    libraryGenreTagsInspectMock.mockImplementation(
+      () => new Promise(resolve => { resolveGenre = resolve; }),
+    );
+
+    renderHook(() => useMigrationOrchestrator());
+
+    // Server-index precheck resolved; genre inspect still pending. The gate must
+    // not be blocking (phase stays 'idle', never 'inspecting'/'running').
+    await waitFor(() => {
+      expect(libraryGenreTagsInspectMock).toHaveBeenCalled();
+    });
+    expect(useMigrationStore.getState().phase).toBe('idle');
+
+    if (!resolveGenre) throw new Error('genre inspect resolver not captured');
+    resolveGenre({ needed: false, totalTracks: 100, doneTracks: 100 });
+
+    await waitFor(() => {
+      expect(useMigrationStore.getState().phase).toBe('completed');
+    });
+  });
+
   it('keeps startup non-blocking while done-flag precheck is pending', async () => {
     localStorage.setItem(DONE_FLAG, '1');
     let resolveInspect: ((value: any) => void) | undefined;

src/hooks/useMigrationOrchestrator.ts

@@ -33,11 +33,11 @@ function buildMappings(): ServerIndexMapping[] {
 
 async function runGenreTagsPhase(): Promise<void> {
   const state = useMigrationStore.getState();
-  state.setStep('genreTags');
   state.setGenreTagsProgress(null);
-  state.setError(null);
-  state.setPhase('inspecting');
 
+  // Inspect first WITHOUT entering a blocking phase. An already-migrated launch
+  // must not flash the gate while this inspect IPC round-trips (regression: the
+  // modal briefly appeared on every startup once the backfill was complete).
   const inspect = await libraryGenreTagsInspect();
   state.setGenreTagsInspect(inspect);
   if (!inspect.needed) {
@@ -45,6 +45,8 @@ async function runGenreTagsPhase(): Promise<void> {
     return;
   }
 
+  state.setStep('genreTags');
+  state.setError(null);
   state.setPhase('running');
   const maxAttempts = 3;
   for (let attempt = 0; attempt < maxAttempts; attempt++) {