diff --git a/src/app/features/tag/store/tag.effects.spec.ts b/src/app/features/tag/store/tag.effects.spec.ts
index 4546f1f743..43791e4d5e 100644
--- a/src/app/features/tag/store/tag.effects.spec.ts
+++ b/src/app/features/tag/store/tag.effects.spec.ts
@@ -11,6 +11,7 @@ import {
 } from '../../work-context/store/work-context.selectors';
 import { selectAllTasksDueToday } from '../../planner/store/planner.selectors';
 import { HydrationStateService } from '../../../op-log/apply/hydration-state.service';
+import { SyncTriggerService } from '../../../imex/sync/sync-trigger.service';
 import { SnackService } from '../../../core/snack/snack.service';
 import { TagService } from '../tag.service';
 import { WorkContextService } from '../../work-context/work-context.service';
@@ -32,6 +33,7 @@ describe('TagEffects', () => {
   let actions$: Observable<any>;
   let store: MockStore;
   let hydrationStateServiceSpy: jasmine.SpyObj<HydrationStateService>;
+  let syncTriggerServiceSpy: jasmine.SpyObj<SyncTriggerService>;
 
   beforeEach(() => {
     actions$ = EMPTY;
@@ -44,6 +46,12 @@ describe('TagEffects', () => {
     hydrationStateServiceSpy.isApplyingRemoteOps.and.returnValue(false);
     hydrationStateServiceSpy.isInSyncWindow.and.returnValue(false);
 
+    syncTriggerServiceSpy = jasmine.createSpyObj('SyncTriggerService', [
+      'isInitialSyncDoneSync',
+    ]);
+    // Default: initial sync is done (so effect should fire)
+    syncTriggerServiceSpy.isInitialSyncDoneSync.and.returnValue(true);
+
     const snackServiceSpy = jasmine.createSpyObj('SnackService', ['open']);
     const tagServiceSpy = jasmine.createSpyObj('TagService', ['updateTag']);
     const workContextServiceSpy = jasmine.createSpyObj('WorkContextService', [], {
@@ -83,6 +91,7 @@ describe('TagEffects', () => {
           ],
         }),
         { provide: HydrationStateService, useValue: hydrationStateServiceSpy },
+        { provide: SyncTriggerService, useValue: syncTriggerServiceSpy },
         { provide: SnackService, useValue: snackServiceSpy },
         { provide: TagService, useValue: tagServiceSpy },
         { provide: WorkContextService, useValue: workContextServiceSpy },
@@ -179,6 +188,27 @@ describe('TagEffects', () => {
       }, 50);
     });
 
+    it('should not dispatch when initial sync is not done', (done) => {
+      // Simulate app startup before first sync
+      syncTriggerServiceSpy.isInitialSyncDoneSync.and.returnValue(false);
+
+      store.overrideSelector(selectTodayTagRepair, {
+        needsRepair: true,
+        repairedTaskIds: ['task1'],
+      });
+      store.refreshState();
+
+      let emitted = false;
+      effects.repairTodayTagConsistency$.subscribe(() => {
+        emitted = true;
+      });
+
+      setTimeout(() => {
+        expect(emitted).toBe(false);
+        done();
+      }, 50);
+    });
+
     it('should handle empty repairedTaskIds', (done) => {
       store.overrideSelector(selectTodayTagRepair, {
         needsRepair: true,
@@ -298,6 +328,27 @@ describe('TagEffects', () => {
       }, 50);
     });
 
+    it('should not dispatch when initial sync is not done', (done) => {
+      syncTriggerServiceSpy.isInitialSyncDoneSync.and.returnValue(false);
+
+      const parent = createTask('parent-1');
+      const child = createTask('child-1', 'parent-1');
+
+      store.overrideSelector(selectTodayTaskIds, ['parent-1', 'child-1']);
+      store.overrideSelector(selectAllTasksDueToday, [parent, child]);
+      store.refreshState();
+
+      let emitted = false;
+      effects.preventParentAndSubTaskInTodayList$.subscribe(() => {
+        emitted = true;
+      });
+
+      setTimeout(() => {
+        expect(emitted).toBe(false);
+        done();
+      }, 50);
+    });
+
     it('should not dispatch when todayTaskIds is empty', (done) => {
       // Empty today list should not trigger the effect
       store.overrideSelector(selectTodayTaskIds, []);
diff --git a/src/app/imex/sync/sync-trigger.service.spec.ts b/src/app/imex/sync/sync-trigger.service.spec.ts
new file mode 100644
index 0000000000..4256d440b5
--- /dev/null
+++ b/src/app/imex/sync/sync-trigger.service.spec.ts
@@ -0,0 +1,115 @@
+import { TestBed } from '@angular/core/testing';
+import { SyncTriggerService } from './sync-trigger.service';
+import { GlobalConfigService } from '../../features/config/global-config.service';
+import { DataInitStateService } from '../../core/data-init/data-init-state.service';
+import { IdleService } from '../../features/idle/idle.service';
+import { PfapiService } from '../../pfapi/pfapi.service';
+import { SyncWrapperService } from './sync-wrapper.service';
+import { Store } from '@ngrx/store';
+import { EMPTY, of, ReplaySubject } from 'rxjs';
+
+describe('SyncTriggerService', () => {
+  let service: SyncTriggerService;
+  let globalConfigService: jasmine.SpyObj<GlobalConfigService>;
+  let dataInitStateService: jasmine.SpyObj<DataInitStateService>;
+  let idleService: jasmine.SpyObj<IdleService>;
+  let pfapiService: jasmine.SpyObj<PfapiService>;
+  let syncWrapperService: jasmine.SpyObj<SyncWrapperService>;
+  let store: jasmine.SpyObj<Store>;
+
+  beforeEach(() => {
+    const isAllDataLoadedSubject = new ReplaySubject<boolean>(1);
+    isAllDataLoadedSubject.next(true);
+
+    globalConfigService = jasmine.createSpyObj('GlobalConfigService', [], {
+      cfg$: of({ sync: { isEnabled: false } }),
+      idle$: of({ isEnableIdleTimeTracking: false }),
+    });
+
+    dataInitStateService = jasmine.createSpyObj('DataInitStateService', [], {
+      isAllDataLoadedInitially$: isAllDataLoadedSubject.asObservable(),
+    });
+
+    idleService = jasmine.createSpyObj('IdleService', [], {
+      isIdle$: of(false),
+    });
+
+    pfapiService = jasmine.createSpyObj('PfapiService', [], {
+      onLocalMetaUpdate$: EMPTY,
+    });
+
+    syncWrapperService = jasmine.createSpyObj('SyncWrapperService', [], {
+      syncProviderId$: of(null),
+      isWaitingForUserInput$: of(false),
+    });
+
+    store = jasmine.createSpyObj('Store', ['select']);
+    store.select.and.returnValue(of(null));
+
+    TestBed.configureTestingModule({
+      providers: [
+        SyncTriggerService,
+        { provide: GlobalConfigService, useValue: globalConfigService },
+        { provide: DataInitStateService, useValue: dataInitStateService },
+        { provide: IdleService, useValue: idleService },
+        { provide: PfapiService, useValue: pfapiService },
+        { provide: SyncWrapperService, useValue: syncWrapperService },
+        { provide: Store, useValue: store },
+      ],
+    });
+
+    service = TestBed.inject(SyncTriggerService);
+  });
+
+  describe('isInitialSyncDoneSync', () => {
+    it('should return false initially', () => {
+      expect(service.isInitialSyncDoneSync()).toBe(false);
+    });
+
+    it('should return true after setInitialSyncDone(true)', () => {
+      service.setInitialSyncDone(true);
+      expect(service.isInitialSyncDoneSync()).toBe(true);
+    });
+
+    it('should return false after setInitialSyncDone(false)', () => {
+      service.setInitialSyncDone(true);
+      expect(service.isInitialSyncDoneSync()).toBe(true);
+
+      service.setInitialSyncDone(false);
+      expect(service.isInitialSyncDoneSync()).toBe(false);
+    });
+
+    it('should track multiple state changes', () => {
+      expect(service.isInitialSyncDoneSync()).toBe(false);
+
+      service.setInitialSyncDone(true);
+      expect(service.isInitialSyncDoneSync()).toBe(true);
+
+      service.setInitialSyncDone(false);
+      expect(service.isInitialSyncDoneSync()).toBe(false);
+
+      service.setInitialSyncDone(true);
+      expect(service.isInitialSyncDoneSync()).toBe(true);
+    });
+  });
+
+  describe('setInitialSyncDone', () => {
+    it('should update both sync flag and observable', (done) => {
+      let observedValue: boolean | undefined;
+
+      // Subscribe to the observable (it's a ReplaySubject internally)
+      service['_isInitialSyncDoneManual$'].subscribe((val) => {
+        observedValue = val;
+      });
+
+      service.setInitialSyncDone(true);
+
+      // Check sync getter
+      expect(service.isInitialSyncDoneSync()).toBe(true);
+
+      // Check observable received the value
+      expect(observedValue).toBe(true);
+      done();
+    });
+  });
+});
diff --git a/src/app/imex/sync/sync-trigger.service.ts b/src/app/imex/sync/sync-trigger.service.ts
index 3bab4aaa7a..eb8e2493c3 100644
--- a/src/app/imex/sync/sync-trigger.service.ts
+++ b/src/app/imex/sync/sync-trigger.service.ts
@@ -150,6 +150,7 @@ export class SyncTriggerService {
   private _isInitialSyncDoneManual$: ReplaySubject<boolean> = new ReplaySubject<boolean>(
     1,
   );
+  private _isInitialSyncDoneSync = false;
   private _isInitialSyncDone$: Observable<boolean> = this._isInitialSyncEnabled$.pipe(
     switchMap((isActive) => {
       if (!isActive) {
@@ -240,6 +241,16 @@ export class SyncTriggerService {
   }
 
   setInitialSyncDone(val: boolean): void {
+    this._isInitialSyncDoneSync = val;
     this._isInitialSyncDoneManual$.next(val);
   }
+
+  /**
+   * Synchronous getter for initial sync done state.
+   * Used by operators like skipDuringSyncWindow() that need
+   * to check state synchronously in filter callbacks.
+   */
+  isInitialSyncDoneSync(): boolean {
+    return this._isInitialSyncDoneSync;
+  }
 }
diff --git a/src/app/util/debounce-during-startup.operator.spec.ts b/src/app/util/debounce-during-startup.operator.spec.ts
new file mode 100644
index 0000000000..af6c7f7370
--- /dev/null
+++ b/src/app/util/debounce-during-startup.operator.spec.ts
@@ -0,0 +1,348 @@
+import { TestBed, fakeAsync, tick } from '@angular/core/testing';
+import { Subject } from 'rxjs';
+import { debounceDuringStartup } from './debounce-during-startup.operator';
+import { SyncTriggerService } from '../imex/sync/sync-trigger.service';
+
+describe('debounceDuringStartup', () => {
+  let syncTriggerService: jasmine.SpyObj<SyncTriggerService>;
+  let source$: Subject<number>;
+
+  beforeEach(() => {
+    syncTriggerService = jasmine.createSpyObj('SyncTriggerService', [
+      'isInitialSyncDoneSync',
+    ]);
+    syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+
+    TestBed.configureTestingModule({
+      providers: [{ provide: SyncTriggerService, useValue: syncTriggerService }],
+    });
+
+    source$ = new Subject<number>();
+  });
+
+  describe('when initial sync is done', () => {
+    beforeEach(() => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+    });
+
+    it('should pass emissions immediately (0ms debounce)', fakeAsync(() => {
+      let result: number | undefined;
+
+      TestBed.runInInjectionContext(() => {
+        source$.pipe(debounceDuringStartup()).subscribe((val) => {
+          result = val;
+        });
+      });
+
+      source$.next(1);
+      tick(0); // Minimal tick for the of(0) debounce
+      expect(result).toBe(1);
+
+      source$.next(2);
+      tick(0);
+      expect(result).toBe(2);
+    }));
+
+    it('should pass through all emissions when sync is done (0ms debounce)', fakeAsync(() => {
+      const results: number[] = [];
+
+      TestBed.runInInjectionContext(() => {
+        source$.pipe(debounceDuringStartup()).subscribe((val) => {
+          results.push(val);
+        });
+      });
+
+      source$.next(1);
+      tick(0);
+      source$.next(2);
+      tick(0);
+      source$.next(3);
+      tick(0);
+
+      // All values pass through immediately when sync is done
+      expect(results).toEqual([1, 2, 3]);
+    }));
+  });
+
+  describe('when initial sync is not done', () => {
+    beforeEach(() => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+    });
+
+    it('should debounce emissions by default 500ms', fakeAsync(() => {
+      let result: number | undefined;
+
+      TestBed.runInInjectionContext(() => {
+        source$.pipe(debounceDuringStartup()).subscribe((val) => {
+          result = val;
+        });
+      });
+
+      source$.next(1);
+      tick(100);
+      expect(result).toBeUndefined();
+
+      tick(400); // Total 500ms
+      expect(result).toBe(1);
+    }));
+
+    it('should debounce emissions by custom time', fakeAsync(() => {
+      let result: number | undefined;
+
+      TestBed.runInInjectionContext(() => {
+        source$.pipe(debounceDuringStartup(200)).subscribe((val) => {
+          result = val;
+        });
+      });
+
+      source$.next(1);
+      tick(100);
+      expect(result).toBeUndefined();
+
+      tick(100); // Total 200ms
+      expect(result).toBe(1);
+    }));
+
+    it('should reset debounce timer on new emissions', fakeAsync(() => {
+      let result: number | undefined;
+
+      TestBed.runInInjectionContext(() => {
+        source$.pipe(debounceDuringStartup(200)).subscribe((val) => {
+          result = val;
+        });
+      });
+
+      source$.next(1);
+      tick(100);
+      expect(result).toBeUndefined();
+
+      // New emission resets the timer
+      source$.next(2);
+      tick(100);
+      expect(result).toBeUndefined();
+
+      tick(100); // 200ms after last emission
+      expect(result).toBe(2);
+    }));
+
+    it('should emit only the latest value after debounce', fakeAsync(() => {
+      const results: number[] = [];
+
+      TestBed.runInInjectionContext(() => {
+        source$.pipe(debounceDuringStartup(200)).subscribe((val) => {
+          results.push(val);
+        });
+      });
+
+      source$.next(1);
+      tick(50);
+      source$.next(2);
+      tick(50);
+      source$.next(3);
+      tick(200);
+
+      expect(results).toEqual([3]);
+    }));
+  });
+
+  describe('state transitions', () => {
+    it('should switch from debounced to immediate when sync completes', fakeAsync(() => {
+      const results: number[] = [];
+
+      TestBed.runInInjectionContext(() => {
+        source$.pipe(debounceDuringStartup(200)).subscribe((val) => {
+          results.push(val);
+        });
+      });
+
+      // Initial sync not done - debounce
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+      source$.next(1);
+      tick(200);
+      expect(results).toEqual([1]);
+
+      // Sync completes - immediate
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+      source$.next(2);
+      tick(0);
+      expect(results).toEqual([1, 2]);
+    }));
+  });
+
+  describe('type preservation', () => {
+    it('should work with different value types', fakeAsync(() => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+      const stringSource$ = new Subject<string>();
+      const results: string[] = [];
+
+      TestBed.runInInjectionContext(() => {
+        stringSource$.pipe(debounceDuringStartup()).subscribe((val) => {
+          results.push(val);
+        });
+      });
+
+      stringSource$.next('a');
+      tick(0);
+      stringSource$.next('b');
+      tick(0);
+
+      expect(results).toEqual(['a', 'b']);
+    }));
+
+    it('should work with object types', fakeAsync(() => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+      const objectSource$ = new Subject<{ id: number }>();
+      const results: { id: number }[] = [];
+
+      TestBed.runInInjectionContext(() => {
+        objectSource$.pipe(debounceDuringStartup()).subscribe((val) => {
+          results.push(val);
+        });
+      });
+
+      objectSource$.next({ id: 1 });
+      tick(0);
+      objectSource$.next({ id: 2 });
+      tick(0);
+
+      expect(results).toEqual([{ id: 1 }, { id: 2 }]);
+    }));
+  });
+
+  describe('edge cases', () => {
+    it('should handle zero debounce time parameter', fakeAsync(() => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+      let result: number | undefined;
+
+      TestBed.runInInjectionContext(() => {
+        source$.pipe(debounceDuringStartup(0)).subscribe((val) => {
+          result = val;
+        });
+      });
+
+      source$.next(1);
+      tick(0);
+
+      expect(result).toBe(1);
+    }));
+
+    it('should handle very long debounce time', fakeAsync(() => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+      let result: number | undefined;
+
+      TestBed.runInInjectionContext(() => {
+        source$.pipe(debounceDuringStartup(5000)).subscribe((val) => {
+          result = val;
+        });
+      });
+
+      source$.next(1);
+      tick(2500);
+      expect(result).toBeUndefined();
+
+      tick(2500); // Total 5000ms
+      expect(result).toBe(1);
+    }));
+
+    it('should emit last value when source completes during debounce', fakeAsync(() => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+      const results: number[] = [];
+      let completed = false;
+
+      TestBed.runInInjectionContext(() => {
+        source$.pipe(debounceDuringStartup(500)).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            completed = true;
+          },
+        });
+      });
+
+      source$.next(1);
+      tick(100);
+      source$.complete();
+      tick(500);
+
+      // RxJS debounce emits the last value on source completion
+      expect(results).toEqual([1]);
+      expect(completed).toBe(true);
+    }));
+  });
+
+  describe('realistic scenarios', () => {
+    it('should debounce rapid state changes during startup', fakeAsync(() => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+      const results: string[] = [];
+
+      TestBed.runInInjectionContext(() => {
+        const events$ = new Subject<string>();
+        events$.pipe(debounceDuringStartup(200)).subscribe((val) => {
+          results.push(val);
+        });
+
+        // Rapid selector emissions during data load
+        events$.next('state-1');
+        tick(50);
+        events$.next('state-2');
+        tick(50);
+        events$.next('state-3');
+        tick(200);
+
+        // Only the final settled state should emit
+        expect(results).toEqual(['state-3']);
+      });
+    }));
+
+    it('should allow immediate emissions after sync completes', fakeAsync(() => {
+      const results: string[] = [];
+
+      TestBed.runInInjectionContext(() => {
+        const events$ = new Subject<string>();
+        events$.pipe(debounceDuringStartup(200)).subscribe((val) => {
+          results.push(val);
+        });
+
+        // During startup - debounced
+        syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+        events$.next('startup-event');
+        tick(200);
+        expect(results).toEqual(['startup-event']);
+
+        // After sync - immediate
+        syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+        events$.next('user-action-1');
+        tick(0);
+        events$.next('user-action-2');
+        tick(0);
+
+        expect(results).toEqual(['startup-event', 'user-action-1', 'user-action-2']);
+      });
+    }));
+
+    it('should handle sync state toggle during debounce period', fakeAsync(() => {
+      const results: number[] = [];
+
+      TestBed.runInInjectionContext(() => {
+        source$.pipe(debounceDuringStartup(300)).subscribe((val) => {
+          results.push(val);
+        });
+      });
+
+      // Start with sync not done - start debouncing
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+      source$.next(1);
+      tick(100);
+
+      // Sync completes mid-debounce
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+      tick(200); // Complete the original debounce
+
+      expect(results).toEqual([1]);
+
+      // Now emissions should be immediate
+      source$.next(2);
+      tick(0);
+      expect(results).toEqual([1, 2]);
+    }));
+  });
+});
diff --git a/src/app/util/debounce-during-startup.operator.ts b/src/app/util/debounce-during-startup.operator.ts
new file mode 100644
index 0000000000..60f50ee030
--- /dev/null
+++ b/src/app/util/debounce-during-startup.operator.ts
@@ -0,0 +1,60 @@
+import { inject } from '@angular/core';
+import { MonoTypeOperatorFunction, of, timer } from 'rxjs';
+import { debounce } from 'rxjs/operators';
+import { SyncTriggerService } from '../imex/sync/sync-trigger.service';
+
+/**
+ * RxJS operator that debounces emissions during startup, then passes through immediately.
+ *
+ * ## Why This Exists
+ *
+ * Unlike `skipDuringSyncWindow()` which completely skips emissions during startup,
+ * this operator allows emissions through after a debounce period. Use this for
+ * effects that:
+ * - Should eventually run during startup (not be skipped entirely)
+ * - But should wait for state to settle before firing
+ *
+ * ## How It Works
+ *
+ * - Before `setInitialSyncDone(true)`: Emissions are debounced by `debounceMs`
+ * - After `setInitialSyncDone(true)`: Emissions pass through immediately (0ms debounce)
+ *
+ * ## When to Use
+ *
+ * Use `debounceDuringStartup()` for effects that:
+ * - Need to run during startup but can wait
+ * - Should let state settle before reacting
+ * - Are not sync-sensitive (won't conflict with remote operations)
+ *
+ * Use `skipDuringSyncWindow()` instead for effects that:
+ * - Modify shared entities (TODAY_TAG, etc.)
+ * - Could create operations that conflict with sync
+ * - Should never run before sync completes
+ *
+ * ## Usage
+ *
+ * ```typescript
+ * import { debounceDuringStartup } from '../../../util/debounce-during-startup.operator';
+ *
+ * @Injectable()
+ * export class MyEffects {
+ *   startupEffect$ = createEffect(() =>
+ *     this.store.select(mySelector).pipe(
+ *       debounceDuringStartup(500),  // Debounce 500ms during startup
+ *       // ... effect logic
+ *     )
+ *   );
+ * }
+ * ```
+ *
+ * @param debounceMs Debounce time in milliseconds during startup (default: 500ms)
+ */
+export const debounceDuringStartup = <T>(
+  debounceMs = 500,
+): MonoTypeOperatorFunction<T> => {
+  const syncTrigger = inject(SyncTriggerService);
+
+  return debounce(() =>
+    syncTrigger.isInitialSyncDoneSync() ? of(0) : timer(debounceMs),
+  );
+};
diff --git a/src/app/util/skip-during-sync-window.operator.spec.ts b/src/app/util/skip-during-sync-window.operator.spec.ts
new file mode 100644
index 0000000000..520e915f22
--- /dev/null
+++ b/src/app/util/skip-during-sync-window.operator.spec.ts
@@ -0,0 +1,339 @@
+import { TestBed } from '@angular/core/testing';
+import { Subject } from 'rxjs';
+import { skipDuringSyncWindow } from './skip-during-sync-window.operator';
+import { HydrationStateService } from '../op-log/apply/hydration-state.service';
+import { SyncTriggerService } from '../imex/sync/sync-trigger.service';
+
+describe('skipDuringSyncWindow', () => {
+  let hydrationStateService: jasmine.SpyObj<HydrationStateService>;
+  let syncTriggerService: jasmine.SpyObj<SyncTriggerService>;
+  let source$: Subject<number>;
+
+  beforeEach(() => {
+    hydrationStateService = jasmine.createSpyObj('HydrationStateService', [
+      'isInSyncWindow',
+    ]);
+    syncTriggerService = jasmine.createSpyObj('SyncTriggerService', [
+      'isInitialSyncDoneSync',
+    ]);
+
+    // Default: initial sync done and not in sync window
+    syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+    hydrationStateService.isInSyncWindow.and.returnValue(false);
+
+    TestBed.configureTestingModule({
+      providers: [
+        { provide: HydrationStateService, useValue: hydrationStateService },
+        { provide: SyncTriggerService, useValue: syncTriggerService },
+      ],
+    });
+
+    source$ = new Subject<number>();
+  });
+
+  describe('initial sync check', () => {
+    it('should skip emissions when initial sync is not done', (done) => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+      hydrationStateService.isInSyncWindow.and.returnValue(false);
+
+      TestBed.runInInjectionContext(() => {
+        const results: number[] = [];
+        source$.pipe(skipDuringSyncWindow()).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            expect(results).toEqual([]);
+            done();
+          },
+        });
+      });
+
+      source$.next(1);
+      source$.next(2);
+      source$.next(3);
+      source$.complete();
+    });
+
+    it('should pass emissions when initial sync is done and not in sync window', (done) => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+      hydrationStateService.isInSyncWindow.and.returnValue(false);
+
+      TestBed.runInInjectionContext(() => {
+        const results: number[] = [];
+        source$.pipe(skipDuringSyncWindow()).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            expect(results).toEqual([1, 2, 3]);
+            done();
+          },
+        });
+      });
+
+      source$.next(1);
+      source$.next(2);
+      source$.next(3);
+      source$.complete();
+    });
+  });
+
+  describe('sync window check', () => {
+    it('should skip emissions when in sync window', (done) => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+      hydrationStateService.isInSyncWindow.and.returnValue(true);
+
+      TestBed.runInInjectionContext(() => {
+        const results: number[] = [];
+        source$.pipe(skipDuringSyncWindow()).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            expect(results).toEqual([]);
+            done();
+          },
+        });
+      });
+
+      source$.next(1);
+      source$.next(2);
+      source$.next(3);
+      source$.complete();
+    });
+
+    it('should skip emissions when both initial sync not done AND in sync window', (done) => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+      hydrationStateService.isInSyncWindow.and.returnValue(true);
+
+      TestBed.runInInjectionContext(() => {
+        const results: number[] = [];
+        source$.pipe(skipDuringSyncWindow()).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            expect(results).toEqual([]);
+            done();
+          },
+        });
+      });
+
+      source$.next(1);
+      source$.next(2);
+      source$.next(3);
+      source$.complete();
+    });
+  });
+
+  describe('dynamic state changes', () => {
+    it('should dynamically filter based on initial sync state', (done) => {
+      TestBed.runInInjectionContext(() => {
+        const results: number[] = [];
+        source$.pipe(skipDuringSyncWindow()).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            expect(results).toEqual([2, 3]);
+            done();
+          },
+        });
+      });
+
+      // Initial sync not done - should skip
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+      source$.next(1);
+
+      // Initial sync done - should pass
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+      source$.next(2);
+      source$.next(3);
+
+      source$.complete();
+    });
+
+    it('should dynamically filter based on sync window state', (done) => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+
+      TestBed.runInInjectionContext(() => {
+        const results: number[] = [];
+        source$.pipe(skipDuringSyncWindow()).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            expect(results).toEqual([1, 3, 5]);
+            done();
+          },
+        });
+      });
+
+      // Not in sync window - should pass
+      hydrationStateService.isInSyncWindow.and.returnValue(false);
+      source$.next(1);
+
+      // Enter sync window - should skip
+      hydrationStateService.isInSyncWindow.and.returnValue(true);
+      source$.next(2);
+
+      // Exit sync window - should pass
+      hydrationStateService.isInSyncWindow.and.returnValue(false);
+      source$.next(3);
+
+      // Enter sync window again - should skip
+      hydrationStateService.isInSyncWindow.and.returnValue(true);
+      source$.next(4);
+
+      // Exit sync window - should pass
+      hydrationStateService.isInSyncWindow.and.returnValue(false);
+      source$.next(5);
+
+      source$.complete();
+    });
+  });
+
+  describe('type preservation', () => {
+    it('should work with different value types', (done) => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+      hydrationStateService.isInSyncWindow.and.returnValue(false);
+
+      TestBed.runInInjectionContext(() => {
+        const stringSource$ = new Subject<string>();
+        const results: string[] = [];
+
+        stringSource$.pipe(skipDuringSyncWindow()).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            expect(results).toEqual(['a', 'b', 'c']);
+            done();
+          },
+        });
+
+        stringSource$.next('a');
+        stringSource$.next('b');
+        stringSource$.next('c');
+        stringSource$.complete();
+      });
+    });
+
+    it('should work with object types', (done) => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+      hydrationStateService.isInSyncWindow.and.returnValue(false);
+
+      TestBed.runInInjectionContext(() => {
+        const objectSource$ = new Subject<{ id: number }>();
+        const results: { id: number }[] = [];
+
+        objectSource$.pipe(skipDuringSyncWindow()).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            expect(results).toEqual([{ id: 1 }, { id: 2 }]);
+            done();
+          },
+        });
+
+        objectSource$.next({ id: 1 });
+        objectSource$.next({ id: 2 });
+        objectSource$.complete();
+      });
+    });
+  });
+
+  describe('realistic scenarios', () => {
+    it('should block during initial startup until first sync completes', (done) => {
+      // Simulate app startup scenario: initial sync not done, not in sync window
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+      hydrationStateService.isInSyncWindow.and.returnValue(false);
+
+      TestBed.runInInjectionContext(() => {
+        const results: string[] = [];
+        const events$ = new Subject<string>();
+
+        events$.pipe(skipDuringSyncWindow()).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            // Only events after initial sync should pass
+            expect(results).toEqual(['user-interaction-3', 'user-interaction-4']);
+            done();
+          },
+        });
+
+        // Effects fire during data load - should be blocked
+        events$.next('effect-during-load-1');
+        events$.next('effect-during-load-2');
+
+        // Initial sync completes
+        syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+
+        // User interactions after sync - should pass
+        events$.next('user-interaction-3');
+        events$.next('user-interaction-4');
+
+        events$.complete();
+      });
+    });
+
+    it('should block during active sync operations', (done) => {
+      syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+
+      TestBed.runInInjectionContext(() => {
+        const results: string[] = [];
+        const events$ = new Subject<string>();
+
+        events$.pipe(skipDuringSyncWindow()).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            expect(results).toEqual(['before-sync', 'after-sync']);
+            done();
+          },
+        });
+
+        // Normal operation
+        hydrationStateService.isInSyncWindow.and.returnValue(false);
+        events$.next('before-sync');
+
+        // Sync starts (e.g., tab focus triggers sync)
+        hydrationStateService.isInSyncWindow.and.returnValue(true);
+        events$.next('during-sync-1');
+        events$.next('during-sync-2');
+
+        // Sync finishes
+        hydrationStateService.isInSyncWindow.and.returnValue(false);
+        events$.next('after-sync');
+
+        events$.complete();
+      });
+    });
+
+    it('should handle rapid state changes correctly', (done) => {
+      TestBed.runInInjectionContext(() => {
+        const results: number[] = [];
+        source$.pipe(skipDuringSyncWindow()).subscribe({
+          next: (val) => results.push(val),
+          complete: () => {
+            expect(results).toEqual([1, 4, 6]);
+            done();
+          },
+        });
+
+        // Allowed
+        syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+        hydrationStateService.isInSyncWindow.and.returnValue(false);
+        source$.next(1);
+
+        // Blocked (initial sync flag flipped)
+        syncTriggerService.isInitialSyncDoneSync.and.returnValue(false);
+        source$.next(2);
+
+        // Blocked (both flags wrong)
+        hydrationStateService.isInSyncWindow.and.returnValue(true);
+        source$.next(3);
+
+        // Allowed (both flags correct)
+        syncTriggerService.isInitialSyncDoneSync.and.returnValue(true);
+        hydrationStateService.isInSyncWindow.and.returnValue(false);
+        source$.next(4);
+
+        // Blocked (sync window only)
+        hydrationStateService.isInSyncWindow.and.returnValue(true);
+        source$.next(5);
+
+        // Allowed again
+        hydrationStateService.isInSyncWindow.and.returnValue(false);
+        source$.next(6);
+
+        source$.complete();
+      });
+    });
+  });
+});
diff --git a/src/app/util/skip-during-sync-window.operator.ts b/src/app/util/skip-during-sync-window.operator.ts
index 841fdfeedf..b8898641dc 100644
--- a/src/app/util/skip-during-sync-window.operator.ts
+++ b/src/app/util/skip-during-sync-window.operator.ts
@@ -2,24 +2,34 @@ import { inject } from '@angular/core';
 import { MonoTypeOperatorFunction } from 'rxjs';
 import { filter } from 'rxjs/operators';
 import { HydrationStateService } from '../op-log/apply/hydration-state.service';
+import { SyncTriggerService } from '../imex/sync/sync-trigger.service';
 
 /**
  * RxJS operator that skips emissions during the full sync window,
- * including the post-sync cooldown period.
+ * including:
+ * - Initial app startup (before first sync completes)
+ * - While remote operations are being applied
+ * - Post-sync cooldown period
  *
  * ## Why This Exists
  *
- * `skipWhileApplyingRemoteOps()` only blocks during `isApplyingRemoteOps()` - the window
- * when operations are being applied to the store. However, there's a timing gap:
+ * There are two timing gaps where selector-based effects could fire and
+ * create operations that conflict with sync:
  *
+ * ### Gap 1: Initial Startup
+ * 1. App loads → data loaded from IndexedDB
+ * 2. Selectors evaluate → effects fire before sync happens
+ * 3. Operations created with stale vector clocks
+ * 4. First sync happens → conflicts with remote operations
+ *
+ * ### Gap 2: Post-Sync
  * 1. Tab gains focus → sync triggers
  * 2. Remote ops applied (isApplyingRemoteOps = true)
  * 3. Sync finishes, isApplyingRemoteOps = false
  * 4. Selectors immediately re-evaluate with new state
  * 5. Effects fire and create operations that conflict with just-synced state
  *
- * This operator extends the suppression window to include a cooldown period
- * after sync, preventing step 5.
+ * This operator blocks during both gaps.
  *
  * ## When to Use
  *
@@ -49,9 +59,12 @@ import { HydrationStateService } from '../op-log/apply/hydration-state.service';
  * | Operator | Suppresses during | Use case |
  * |----------|-------------------|----------|
  * | skipWhileApplyingRemoteOps() | isApplyingRemoteOps only | General selector-based effects |
- * | skipDuringSyncWindow() | isApplyingRemoteOps + cooldown | Effects that modify shared entities |
+ * | skipDuringSyncWindow() | startup + isApplyingRemoteOps + cooldown | Effects that modify shared entities |
  */
 export const skipDuringSyncWindow = <T>(): MonoTypeOperatorFunction<T> => {
   const hydrationState = inject(HydrationStateService);
-  return filter(() => !hydrationState.isInSyncWindow());
+  const syncTrigger = inject(SyncTriggerService);
+  return filter(
+    () => syncTrigger.isInitialSyncDoneSync() && !hydrationState.isInSyncWindow(),
+  );
 };