fixes and improvements

backend/src/media_library_viewer_api/clients/ssh.py

@@ -20,6 +20,8 @@ from typing import Any
 
 import paramiko
 
+from media_library_viewer_api.services.known_hosts import has_known_host
+
 logger = logging.getLogger(__name__)
 
 
@@ -64,17 +66,23 @@ class RemoteSSHClient:
     def connect(self) -> paramiko.SSHClient:
         """Create or reuse the Paramiko connection.
 
-        Host keys are expected to be managed ahead of time by startup synthesis
-        or explicit validation flows. Runtime connections only load the managed
-        known_hosts file and then let Paramiko enforce strict checking.
+        Host keys are trusted on first successful use when a managed
+        known_hosts path is configured. Subsequent connections stay strict and
+        reject host-key changes.
         """
         if self._client:
             return self._client
         client = paramiko.SSHClient()
         client.load_system_host_keys()
-        if self.known_hosts_path and Path(self.known_hosts_path).is_file():
-            client.load_host_keys(self.known_hosts_path)
-        client.set_missing_host_key_policy(paramiko.RejectPolicy())
+        known_hosts_file = Path(self.known_hosts_path) if self.known_hosts_path else None
+        trusted_before = bool(
+            known_hosts_file and has_known_host(self.host, self.port, known_hosts_file)
+        )
+        if known_hosts_file and known_hosts_file.is_file():
+            client.load_host_keys(str(known_hosts_file))
+        client.set_missing_host_key_policy(
+            paramiko.RejectPolicy() if trusted_before else paramiko.AutoAddPolicy()
+        )
         connect_kwargs: dict[str, Any] = {
             "hostname": self.host,
             "port": self.port,
@@ -103,6 +111,9 @@ class RemoteSSHClient:
                     "Check the selected key, passphrase, username, or password."
                 ) from exc
             raise
+        if known_hosts_file and not trusted_before:
+            known_hosts_file.parent.mkdir(parents=True, exist_ok=True)
+            client.save_host_keys(str(known_hosts_file))
         self._client = client
         return client
 

backend/src/media_library_viewer_api/dependencies.py

@@ -12,7 +12,7 @@ import logging
 from functools import lru_cache
 from typing import Any
 
-from fastapi import Request
+from fastapi import HTTPException, Request
 
 from media_library_viewer_api.clients.jellyfin import JellyfinClient
 from media_library_viewer_api.clients.jellyseerr import JellyseerrClient
@@ -82,6 +82,27 @@ def _ssh_client_for(cache_key: tuple[str, str, str, int, str, str | None, str |
     )
     try:
         client.connect()
+    except RuntimeError as exc:
+        message = str(exc)
+        lowered = message.lower()
+        logger.exception("Failed to establish SSH connection to %s", host or "<unset>")
+        if "banner" in lowered:
+            raise HTTPException(
+                status_code=502,
+                detail=(
+                    f"SSH banner not received from {host}:{port}. "
+                    "Confirm the host, port, and firewall; the backend could not complete the SSH handshake."
+                ),
+            ) from exc
+        if "authentication failed" in lowered or "no authentication methods available" in lowered:
+            raise HTTPException(
+                status_code=401,
+                detail=(
+                    f"SSH authentication failed for {host}:{port}. "
+                    "Check the selected key, passphrase, username, or password."
+                ),
+            ) from exc
+        raise HTTPException(status_code=502, detail=message) from exc
     except Exception:
         logger.exception("Failed to establish SSH connection to %s", host or "<unset>")
         raise

backend/src/media_library_viewer_api/routers/settings.py

@@ -13,7 +13,7 @@ from media_library_viewer_api.clients.ssh import RemoteSSHClient
 from media_library_viewer_api.config import get_settings
 from media_library_viewer_api.dependencies import get_monitoring_poller, get_settings_store
 from media_library_viewer_api.services.db_maintenance import remove_sqlite_database
-from media_library_viewer_api.services.known_hosts import ensure_known_host
+from media_library_viewer_api.services.known_hosts import has_known_host
 from media_library_viewer_api.services.media_index import MediaIndex
 from media_library_viewer_api.services.settings_store import SettingsStore
 
@@ -98,20 +98,7 @@ def test_machine_ssh(
 
     client, host, port = _resolve_ssh_client(machine, store)
     settings = get_settings()
-    try:
-        known_hosts_updated = ensure_known_host(host, port, settings.ssh_known_hosts_file, strict=True)
-    except RuntimeError as exc:
-        message = str(exc)
-        lowered = message.lower()
-        if "protocol banner" in lowered:
-            raise HTTPException(
-                status_code=status.HTTP_502_BAD_GATEWAY,
-                detail=(
-                    f"SSH banner not received from {host}:{port}; the backend could not record the host key. "
-                    "Confirm the SSH service, host, and port are reachable."
-                ),
-            ) from exc
-        raise HTTPException(status_code=status.HTTP_502_BAD_GATEWAY, detail=message) from exc
+    known_hosts_updated = not has_known_host(host, port, settings.ssh_known_hosts_file)
 
     try:
         client.connect()

backend/src/media_library_viewer_api/services/known_hosts.py

@@ -41,6 +41,16 @@ def _fetch_server_key(host: str, port: int, timeout: int = 30) -> paramiko.PKey:
         sock.close()
 
 
+def has_known_host(host: str, port: int, known_hosts_path: Path) -> bool:
+    """Return whether the given host/port is already present in known_hosts."""
+    if not host or not known_hosts_path.exists():
+        return False
+    host_alias = _host_alias(host, port)
+    host_keys = paramiko.HostKeys()
+    host_keys.load(str(known_hosts_path))
+    return host_keys.lookup(host_alias) is not None
+
+
 def ensure_known_host(host: str, port: int, known_hosts_path: Path, *, strict: bool = True) -> bool:
     """Ensure a host key entry exists for the given host/port.