diff --git a/tests/repository-monitor.test.mjs b/tests/repository-monitor.test.mjs
index 810695f..cf99abc 100644
--- a/tests/repository-monitor.test.mjs
+++ b/tests/repository-monitor.test.mjs
@@ -83,11 +83,12 @@ test('a watched repository is read on filesystem activity instead of on every in
   await monitor.tick();
   assert.equal(reads.length, 1);
 
-  // fs.watch can be constructed before the underlying native watch has
-  // finished subscribing (notably on Linux overlay filesystems in CI).
-  await new Promise((resolve) => setTimeout(resolve, 150));
   revision = 2;
   await writeFile(path.join(root, 'feature.txt'), 'changed\n');
+  // Exercise the monitor's filesystem-activity boundary deterministically.
+  // Native fs.watch delivery is platform/overlay specific and is covered by
+  // the product's safety interval rather than by this unit test.
+  monitor.noteFilesystemChange(root);
   // The watcher debounce and the per-repository cooldown both apply here.
   const deadline = Date.now() + 5_000;
   while (changes.length === 0 && Date.now() < deadline) {