diff --git a/src/lib/stores/focusTimer.svelte.ts b/src/lib/stores/focusTimer.svelte.ts
index fd21739..05d855c 100644
--- a/src/lib/stores/focusTimer.svelte.ts
+++ b/src/lib/stores/focusTimer.svelte.ts
@@ -201,6 +201,11 @@ function createFocusTimerStore() {
       completionFlashUntil = Date.now() + 3000;
       completionFired = true;
       fireCompletion();
+      // startTick() is REQUIRED here: tick() is the only thing that
+      // observes `now >= completionFlashUntil` and calls clear(). Without
+      // it, the completion flash would stay visible until the user
+      // interacts with the app. stopTick() runs via clear() once the
+      // flash window elapses.
       startTick();
       return;
     }