implement fs shims

shims/fs/watch.js

@@ -0,0 +1,57 @@
+// File watching shim
+// Translates fs.watch() calls into WebSocket subscriptions.
+// The server pushes file-change events; this module dispatches them
+// to registered watch listeners.
+
+export function createFsWatch(transport) {
+  const watchers = new Map(); // path -> Set<listener>
+
+  return {
+    watch(path, options, listener) {
+      if (typeof options === 'function') {
+        listener = options;
+        options = {};
+      }
+
+      if (!watchers.has(path)) {
+        watchers.set(path, new Set());
+      }
+      watchers.get(path).add(listener);
+
+      // TODO: send watch subscription to server via transport
+
+      // Return a watcher-like object
+      return {
+        close() {
+          const set = watchers.get(path);
+          if (set) {
+            set.delete(listener);
+            if (set.size === 0) {
+              watchers.delete(path);
+              // TODO: send unwatch to server
+            }
+          }
+        },
+        on() { return this; },
+        once() { return this; },
+        removeListener() { return this; },
+      };
+    },
+
+    // Internal: called when transport receives a file-change event
+    _dispatch(eventType, filePath) {
+      for (const [watchPath, listeners] of watchers) {
+        if (filePath === watchPath || filePath.startsWith(watchPath + '/')) {
+          const relativeName = filePath.slice(watchPath.length + 1) || filePath;
+          for (const fn of listeners) {
+            try {
+              fn(eventType, relativeName);
+            } catch (e) {
+              console.error('[shim:fs:watch] Listener error:', e);
+            }
+          }
+        }
+      }
+    },
+  };
+}