diff --git a/tests/lsp/worker_map_test.mjs b/tests/lsp/worker_map_test.mjs
index 3eb2c773..864615f0 100644
--- a/tests/lsp/worker_map_test.mjs
+++ b/tests/lsp/worker_map_test.mjs
@@ -136,6 +136,13 @@ function workerBootstrap() {
   fs.watch = (directory, ...args) => {
     const listener = args.pop();
     const watcher = watch(directory, ...args, (event, filename) => {
+      // macOS FSEvents can drop a change made while the stream starts; the worker must not need it.
+      if (
+        directory === registrationParent &&
+        filename === path.basename(path.dirname(registrationDirectory))
+      ) {
+        return;
+      }
       const sibling = path.basename(workerData.ancestorNoise);
       if (
         directory === workerData.workspaceRoot &&
diff --git a/tools/tsserver-hook-worker.js b/tools/tsserver-hook-worker.js
index 55789bf8..8c341a1c 100644
--- a/tools/tsserver-hook-worker.js
+++ b/tools/tsserver-hook-worker.js
@@ -20,6 +20,8 @@ const BUILD_FILES = new Set(['BUILD.bazel', 'BUILD']);
 
 const DEBUG = !!process.env.TSSERVER_HOOK_DEBUG;
 const directoryWatchers = new Map();
+// Declared before the initial build, whose watch attachment may already schedule a rebuild.
+let rebuildTimer = null;
 
 function log(msg) {
   if (DEBUG) {
@@ -315,8 +317,6 @@ parentPort.postMessage({ type: 'resolution-map', data: initialMap });
 
 // ── File-system watchers ──────────────────────────────────────────────────────
 
-let rebuildTimer = null;
-
 function scheduleRebuild() {
   if (rebuildTimer) return;
   rebuildTimer = setTimeout(() => {
@@ -386,6 +386,14 @@ function watchDirectory(dir, root, watched, filename) {
               scheduleRebuild();
             }
           });
+          // A directory replaced while its watch attaches may never send an event (macOS FSEvents).
+          let attached;
+          try {
+            attached = fs.statSync(canonical);
+          } catch (_) {}
+          if (!attached || attached.dev !== stat.dev || attached.ino !== stat.ino) {
+            scheduleRebuild();
+          }
         } else {
           current.filter = filter;
         }