fix: SSH keepalive + auto-reconnect for SFTP and terminal

- Add transport.set_keepalive(30) to all SSH connections
- Add SFTPSession.reconnect() method
- Auto-reconnect in _refresh_remote with retry on failure
- Auto-reconnect before upload/download operations
- Guard all remote navigation methods with connection checks
- ShellSession.connected wrapped in try/except
- Terminal: reset reconnect counter on send failure, increase max to 5
- Terminal: trigger reconnect on send to dead session

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

core/ssh_client.py

@@ -45,6 +45,9 @@ def _connect_client(server: dict, key_path: str, timeout: int = 15) -> paramiko.
         try:
             kwargs["key_filename"] = key_path
             client.connect(**kwargs)
+            transport = client.get_transport()
+            if transport is not None:
+                transport.set_keepalive(30)
             return client
         except paramiko.AuthenticationException:
             log.debug(f"Key auth failed for {server.get('alias', '?')}, trying password")
@@ -68,6 +71,9 @@ def _connect_client(server: dict, key_path: str, timeout: int = 15) -> paramiko.
         kwargs["look_for_keys"] = False
         kwargs["allow_agent"] = False
         client.connect(**kwargs)
+        transport = client.get_transport()
+        if transport is not None:
+            transport.set_keepalive(30)
         return client
 
     raise Exception(f"No auth method for {server.get('alias', 'unknown')}")
@@ -92,11 +98,14 @@ class ShellSession:
 
     @property
     def connected(self) -> bool:
-        return (
-            self._channel is not None
-            and self._channel.get_transport() is not None
-            and self._channel.get_transport().is_active()
-        )
+        try:
+            return (
+                self._channel is not None
+                and self._channel.get_transport() is not None
+                and self._channel.get_transport().is_active()
+            )
+        except Exception:
+            return False
 
     def connect(self):
         self._client = _connect_client(self.server, self.key_path)
@@ -334,6 +343,12 @@ class SFTPSession:
         self._client = _connect_client(self.server, self.key_path)
         self._sftp = self._client.open_sftp()
 
+    def reconnect(self):
+        """Disconnect and re-establish SFTP session."""
+        self.disconnect()
+        time.sleep(0.2)
+        self.connect()
+
     def disconnect(self):
         if self._sftp:
             try: