feat(watchers): add Rust-powered watcher backend with runtime fallback and cross-platform test coverage

ts/watchers/watcher.node.ts

@@ -17,11 +17,19 @@ import type { IWatcher, IWatcherOptions, IWatchEvent } from './interfaces.js';
 export class NodeWatcher implements IWatcher {
   private watcher: chokidar.FSWatcher | null = null;
   private _isWatching = false;
+  private _preExistingHandles: Set<any> = new Set();
 
   public readonly events$ = new smartrx.rxjs.Subject<IWatchEvent>();
 
   constructor(private options: IWatcherOptions) {}
 
+  /** Collect all current FSWatcher handles from the process */
+  private _getFsWatcherHandles(): any[] {
+    return (process as any)._getActiveHandles().filter(
+      (h: any) => h?.constructor?.name === 'FSWatcher' && typeof h.unref === 'function'
+    );
+  }
+
   get isWatching(): boolean {
     return this._isWatching;
   }
@@ -29,6 +37,9 @@ export class NodeWatcher implements IWatcher {
   async start(): Promise<void> {
     if (this._isWatching) return;
 
+    // Snapshot existing FSWatcher handles so we only unref ours on stop
+    this._preExistingHandles = new Set(this._getFsWatcherHandles());
+
     console.log(`[smartwatch] Starting chokidar watcher for ${this.options.basePaths.length} base path(s)...`);
 
     try {
@@ -90,13 +101,16 @@ export class NodeWatcher implements IWatcher {
       this.watcher = null;
     }
 
-    // Unref any lingering FSWatcher handles from chokidar so they don't prevent process exit.
-    // Chokidar v5's close() resolves before all fs.watch() handles are fully released.
-    for (const handle of (process as any)._getActiveHandles()) {
-      if (handle?.constructor?.name === 'FSWatcher' && typeof handle.unref === 'function') {
+    // Unref only FSWatcher handles created during our watch session.
+    // Chokidar v5 can orphan fs.watch() handles under heavy file churn,
+    // preventing process exit. We only touch handles that didn't exist
+    // before start() to avoid affecting other watchers in the process.
+    for (const handle of this._getFsWatcherHandles()) {
+      if (!this._preExistingHandles.has(handle)) {
         handle.unref();
       }
     }
+    this._preExistingHandles.clear();
 
     this._isWatching = false;
     console.log('[smartwatch] Watcher stopped');