Auto-refresh the active tab's panels (silent, non-disturbing)

Local panels are fs.watched (LocalDirWatcher + setWatchedDirs -> pathRefresh);
remote panels poll every 3s. New refresh({silent}) skips the loading/busy
flags and touches no DOM, snapshotting sessionId+cwd to discard results if the
user navigated mid-flight. Only the active tab is live; switching tabs
refreshes the new pair. A future on/off setting is left as commented
breadcrumbs. Docs updated.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/bun/fs/watcher.ts

@@ -0,0 +1,64 @@
+import { type FSWatcher, watch } from "node:fs";
+
+const DEBOUNCE_MS = 150;
+
+/**
+ * Watches a set of local directories with node's fs.watch and fires onChange
+ * (debounced per dir — fs.watch emits bursts) when their contents change. Used
+ * to auto-refresh the active tab's local panels instantly; SFTP has no
+ * equivalent, so remote panels are polled UI-side instead.
+ *
+ * onChange is late-bound (assigned after the RPC exists, like AppDeps.events)
+ * so it can push pathRefresh to the main webview.
+ */
+export class LocalDirWatcher {
+	onChange: (dir: string) => void = () => {};
+	private readonly handles = new Map<string, FSWatcher>();
+	private readonly debounces = new Map<string, ReturnType<typeof setTimeout>>();
+
+	/** Replace the watched set: drop handles no longer wanted, open new ones. */
+	setWatched(dirs: string[]): void {
+		const wanted = new Set(dirs);
+		for (const [dir, handle] of this.handles) {
+			if (!wanted.has(dir)) {
+				handle.close();
+				this.handles.delete(dir);
+			}
+		}
+		for (const dir of wanted) {
+			if (this.handles.has(dir)) continue;
+			try {
+				const handle = watch(dir, () => this.fire(dir));
+				// a watched dir that gets deleted/unmounted errors — just drop it
+				handle.on("error", () => this.drop(dir));
+				this.handles.set(dir, handle);
+			} catch {
+				// dir vanished between listing and watching — ignore
+			}
+		}
+	}
+
+	private fire(dir: string): void {
+		const pending = this.debounces.get(dir);
+		if (pending) clearTimeout(pending);
+		this.debounces.set(
+			dir,
+			setTimeout(() => {
+				this.debounces.delete(dir);
+				this.onChange(dir);
+			}, DEBOUNCE_MS),
+		);
+	}
+
+	private drop(dir: string): void {
+		this.handles.get(dir)?.close();
+		this.handles.delete(dir);
+	}
+
+	dispose(): void {
+		for (const handle of this.handles.values()) handle.close();
+		this.handles.clear();
+		for (const pending of this.debounces.values()) clearTimeout(pending);
+		this.debounces.clear();
+	}
+}