Fix relay URL derivation stripping existing port before appending :8765

http://10.10.20.70:3000 was becoming ws://10.10.20.70:3000:8765 instead
of ws://10.10.20.70:8765. Extract hostname only via urlparse.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agent/agent.py

@@ -358,6 +358,23 @@ class Agent:
         self._stop_event.set()
 
 
+# ── Helpers ───────────────────────────────────────────────────────────────────
+
+def _default_relay_url(server_url: str) -> str:
+    """Derive the relay WebSocket URL from a server HTTP URL.
+
+    Strips any existing port, swaps the scheme, and appends :8765.
+    e.g. http://10.10.20.70:3000  →  ws://10.10.20.70:8765
+         https://remotelink.example.com  →  wss://remotelink.example.com:8765
+    """
+    from urllib.parse import urlparse, urlunparse
+    parsed = urlparse(server_url)
+    ws_scheme = "wss" if parsed.scheme == "https" else "ws"
+    # netloc may include a port — strip it, use only the hostname
+    host = parsed.hostname
+    return f"{ws_scheme}://{host}:8765"
+
+
 # ── Entry point ───────────────────────────────────────────────────────────────
 
 def setup_logging(verbose: bool):
@@ -396,7 +413,7 @@ async def main():
             sys.exit(1)
         log.info(f"Enrolling with server {args.server}…")
         reg = await register(args.server, args.enroll)
-        relay_url = args.relay or args.server.replace("https://", "ws://").replace("http://", "ws://") + ":8765"
+        relay_url = args.relay or _default_relay_url(args.server)
         config = {
             "server_url": args.server,
             "relay_url": relay_url,
@@ -414,9 +431,7 @@ async def main():
         sys.exit(1)
 
     server_url = config["server_url"]
-    relay_url = config.get("relay_url") or (
-        server_url.replace("https://", "ws://").replace("http://", "ws://") + ":8765"
-    )
+    relay_url = config.get("relay_url") or _default_relay_url(server_url)
     machine_id = config["machine_id"]
     access_key = config["access_key"]