fix(whatsapp): replace Linux-only fuser with cross-platform port cleanup

fuser command does not exist on Windows, causing orphaned bridge processes
to never be cleaned up. On crash recovery, the port stays occupied and the
next connect() fails with address-already-in-use.

Add _kill_port_process() helper that uses netstat+taskkill on Windows and
fuser on Linux/macOS. Replace both call sites in connect() and disconnect().

gateway/platforms/whatsapp.py

@@ -28,6 +28,41 @@ from typing import Dict, List, Optional, Any
 
 logger = logging.getLogger(__name__)
 
+
+def _kill_port_process(port: int) -> None:
+    """Kill any process listening on the given TCP port."""
+    try:
+        if _IS_WINDOWS:
+            # Use netstat to find the PID bound to this port, then taskkill
+            result = subprocess.run(
+                ["netstat", "-ano", "-p", "TCP"],
+                capture_output=True, text=True, timeout=5,
+            )
+            for line in result.stdout.splitlines():
+                parts = line.split()
+                if len(parts) >= 5 and parts[3] == "LISTENING":
+                    local_addr = parts[1]
+                    if local_addr.endswith(f":{port}"):
+                        try:
+                            subprocess.run(
+                                ["taskkill", "/PID", parts[4], "/F"],
+                                capture_output=True, timeout=5,
+                            )
+                        except subprocess.SubprocessError:
+                            pass
+        else:
+            result = subprocess.run(
+                ["fuser", f"{port}/tcp"],
+                capture_output=True, timeout=5,
+            )
+            if result.returncode == 0:
+                subprocess.run(
+                    ["fuser", "-k", f"{port}/tcp"],
+                    capture_output=True, timeout=5,
+                )
+    except Exception:
+        pass
+
 import sys
 sys.path.insert(0, str(Path(__file__).resolve().parents[2]))
 
@@ -145,21 +180,9 @@ class WhatsAppAdapter(BasePlatformAdapter):
             self._session_path.mkdir(parents=True, exist_ok=True)
             
             # Kill any orphaned bridge from a previous gateway run
-            try:
-                result = subprocess.run(
-                    ["fuser", f"{self._bridge_port}/tcp"],
-                    capture_output=True, timeout=5,
-                )
-                if result.returncode == 0:
-                    # Port is in use — kill the process
-                    subprocess.run(
-                        ["fuser", "-k", f"{self._bridge_port}/tcp"],
-                        capture_output=True, timeout=5,
-                    )
-                    import time
-                    time.sleep(2)
-            except Exception:
-                pass
+            _kill_port_process(self._bridge_port)
+            import time
+            time.sleep(1)
             
             # Start the bridge process in its own process group.
             # Route output to a log file so QR codes, errors, and reconnection
@@ -293,13 +316,7 @@ class WhatsAppAdapter(BasePlatformAdapter):
                 print(f"[{self.name}] Error stopping bridge: {e}")
         
         # Also kill any orphaned bridge processes on our port
-        try:
-            subprocess.run(
-                ["fuser", "-k", f"{self._bridge_port}/tcp"],
-                capture_output=True, timeout=5,
-            )
-        except Exception:
-            pass
+        _kill_port_process(self._bridge_port)
         
         self._running = False
         self._bridge_process = None