feat: add remote trust and server identity pinning

- Add SSH-style server identity keys and known-host verification for remote serve endpoints.
- Add remote add/list/remove commands for explicit endpoint persistence.
- Fix remote clients listing to fan out through target discovery instead of ambiguous auto-routing.
- Add URL glob matching for tabs filter and count with extension tests.
- Add n8n credential pinning for server public keys or SHA256 fingerprints.
- Remove obsolete compat shim behavior while keeping empty compat seams for future protocol changes.
- Bump browser-cli to 0.16.4 and n8n node to 0.3.1.
- Cover known-hosts, remote registry, compat seams, n8n protocol verification, and URL matching with tests.

browser_cli/remote/known_hosts.py

@@ -0,0 +1,108 @@
+"""SSH-style known-hosts pinning for browser-cli remote servers."""
+from __future__ import annotations
+
+import json
+import os
+import sys
+from pathlib import Path
+
+from browser_cli.constants import CONFIG_DIR
+from browser_cli.endpoints import _normalize_endpoint
+from browser_cli.errors import BrowserNotConnected
+
+KNOWN_HOSTS_PATH = CONFIG_DIR / "known_hosts.json"
+
+def fingerprint(pubkey_hex: str) -> str:
+  """Return a compact SHA256 fingerprint for display."""
+  import base64
+  import hashlib
+
+  digest = hashlib.sha256(bytes.fromhex(pubkey_hex)).digest()
+  return "SHA256:" + base64.b64encode(digest).decode("ascii").rstrip("=")
+
+def load_known_hosts(path: Path | None = None) -> dict[str, str]:
+  path = path or KNOWN_HOSTS_PATH
+  if not path.exists():
+    return {}
+  try:
+    data = json.loads(path.read_text(encoding="utf-8"))
+  except Exception:
+    return {}
+  if not isinstance(data, dict):
+    return {}
+  return {_normalize_endpoint(str(endpoint)): str(pubkey) for endpoint, pubkey in data.items() if isinstance(pubkey, str)}
+
+def save_known_host(endpoint: str, pubkey_hex: str, path: Path | None = None) -> None:
+  path = path or KNOWN_HOSTS_PATH
+  known = load_known_hosts(path)
+  known[_normalize_endpoint(endpoint)] = pubkey_hex
+  path.parent.mkdir(parents=True, exist_ok=True)
+  fd = os.open(str(path), os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
+  with os.fdopen(fd, "w", encoding="utf-8") as file:
+    file.write(json.dumps(known, indent=2, sort_keys=True) + "\n")
+
+def remove_known_host(endpoint: str, path: Path | None = None) -> bool:
+  path = path or KNOWN_HOSTS_PATH
+  known = load_known_hosts(path)
+  normalized = _normalize_endpoint(endpoint)
+  if normalized not in known:
+    return False
+  del known[normalized]
+  path.parent.mkdir(parents=True, exist_ok=True)
+  fd = os.open(str(path), os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
+  with os.fdopen(fd, "w", encoding="utf-8") as file:
+    file.write(json.dumps(known, indent=2, sort_keys=True) + "\n")
+  return True
+
+def _is_loopback_endpoint(endpoint: str) -> bool:
+  host, sep, _port = endpoint.rpartition(":")
+  check = host if sep else endpoint
+  return check in {"127.0.0.1", "localhost", "::1"}
+
+def verify_known_host(endpoint: str, challenge: dict | None) -> None:
+  """Verify and pin the server identity from a challenge frame.
+
+  First contact auto-adds the host when the process is interactive, mirroring
+  SSH's trust-on-first-use flow. Non-interactive clients must pin explicitly via
+  `browser-cli remote trust-host ENDPOINT`.
+  """
+  if not isinstance(challenge, dict):
+    return
+  pubkey = challenge.get("server_pubkey")
+  if not isinstance(pubkey, str) or not pubkey:
+    return
+
+  from browser_cli.auth.server_identity import verify_challenge_signature
+  if not verify_challenge_signature(challenge):
+    raise BrowserNotConnected("Remote server identity signature is invalid")
+
+  normalized = _normalize_endpoint(endpoint)
+  known = load_known_hosts()
+  expected = known.get(normalized)
+  if expected is None and _is_loopback_endpoint(endpoint):
+    return
+  if expected is None:
+    if not sys.stdin.isatty():
+      raise BrowserNotConnected(
+        f"Unknown remote server identity for {normalized} ({fingerprint(pubkey)}).\n"
+        f"Run: browser-cli remote trust-host {normalized}"
+      )
+    sys.stderr.write(
+      f"The authenticity of remote '{normalized}' can't be established.\n"
+      f"Server key fingerprint is {fingerprint(pubkey)}.\n"
+      "Trust this server and add it to known hosts? [y/N] "
+    )
+    answer = sys.stdin.readline().strip().lower()
+    if answer not in {"y", "yes"}:
+      raise BrowserNotConnected("Remote server identity was not trusted")
+    save_known_host(normalized, pubkey)
+    sys.stderr.write(f"Added {normalized} to browser-cli known hosts.\n")
+    return
+
+  if expected != pubkey:
+    raise BrowserNotConnected(
+      f"REMOTE SERVER IDENTITY CHANGED for {normalized}!\n"
+      f"Known: {fingerprint(expected)}\n"
+      f"Seen:  {fingerprint(pubkey)}\n"
+      f"If this is expected, run: browser-cli remote untrust-host {normalized} && browser-cli remote trust-host {normalized}"
+    )

browser_cli/remote/registry.py

@@ -28,18 +28,39 @@ def is_valid_key_spec(value: str) -> bool:
     not value.startswith("<") and ("/" in value or Path(value).suffix in {".pem", ".key"})
   )
 
-def save_remote_key(endpoint: str, key_spec: str) -> None:
-  """Persist the key spec (e.g. 'agent' or a file path) for a remote endpoint."""
-  if not endpoint or not key_spec or not is_valid_key_spec(key_spec):
+def save_remote(endpoint: str, key_spec: str | None = None) -> None:
+  """Persist a remote endpoint, optionally with a key spec."""
+  if not endpoint:
     return
+  normalized = _normalize_endpoint(endpoint)
   remotes = load_remotes()
-  current = remotes.get(endpoint, {})
-  current["key"] = key_spec
-  remotes[endpoint] = current
+  current = remotes.get(normalized, {})
+  if key_spec:
+    if not is_valid_key_spec(key_spec):
+      return
+    current["key"] = key_spec
+  remotes[normalized] = current
   REMOTE_REGISTRY_PATH.parent.mkdir(parents=True, exist_ok=True)
   fd = os.open(str(REMOTE_REGISTRY_PATH), os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
   with os.fdopen(fd, "w", encoding="utf-8") as f:
-    f.write(json.dumps(remotes, indent=2, sort_keys=True))
+    f.write(json.dumps(remotes, indent=2, sort_keys=True) + "\n")
+
+def remove_remote(endpoint: str) -> bool:
+  """Remove a remembered remote endpoint. Returns True when it existed."""
+  normalized = _normalize_endpoint(endpoint)
+  remotes = load_remotes()
+  if normalized not in remotes:
+    return False
+  del remotes[normalized]
+  REMOTE_REGISTRY_PATH.parent.mkdir(parents=True, exist_ok=True)
+  fd = os.open(str(REMOTE_REGISTRY_PATH), os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
+  with os.fdopen(fd, "w", encoding="utf-8") as f:
+    f.write(json.dumps(remotes, indent=2, sort_keys=True) + "\n")
+  return True
+
+def save_remote_key(endpoint: str, key_spec: str) -> None:
+  """Persist the key spec (e.g. 'agent' or a file path) for a remote endpoint."""
+  save_remote(endpoint, key_spec)
 
 def key_for_remote(endpoint: str | None) -> str | None:
   if not endpoint:

browser_cli/remote/transport.py

@@ -28,6 +28,7 @@ from browser_cli.remote.socket import (
   split_endpoint as _split_endpoint,
 )
 from browser_cli.remote import pool as _pool
+from browser_cli.remote.known_hosts import verify_known_host
 
 def _send_remote(endpoint: str, msg: dict, private_key=None, *, warn_no_pq: bool | None = None) -> bytes | None:
   # Reuse an already-authenticated connection when one is idle for this endpoint.
@@ -51,7 +52,10 @@ def _send_remote_handshake(endpoint: str, msg: dict, private_key=None, *, warn_n
 
   sock = _connect_socket(endpoint)
   try:
-    payload_msg, pq_shared_secret = _with_challenge(_recv_all(sock), msg, private_key, build_auth)
+    challenge_raw = _recv_all(sock)
+    challenge, _nonce_hex = _parse_challenge(challenge_raw)
+    verify_known_host(endpoint, challenge)
+    payload_msg, pq_shared_secret = _with_challenge(challenge_raw, msg, private_key, build_auth)
     sock.sendall(frame(json.dumps(payload_msg).encode("utf-8")))
     response = _decode_pq_response(_recv_all(sock), pq_shared_secret)
   except BaseException:
@@ -69,6 +73,8 @@ async def _send_remote_async(endpoint: str, msg: dict, private_key=None, *, warn
   reader, writer = await _open_async_connection(endpoint)
   try:
     challenge_raw = await _async_recv_all(reader)
+    challenge, _nonce_hex = _parse_challenge(challenge_raw)
+    verify_known_host(endpoint, challenge)
     warn = _should_warn_no_pq(msg) if warn_no_pq is None else warn_no_pq
 
     async def build_auth(sync_msg: dict, challenge: dict | None, nonce_hex: str | None, key):