v1.8.2: session management hardening

- Fix infinite reconnect loop in terminal (_send_to_shell guard)
- Safe language switch: disconnect + reconnect instead of object transplant
- Improved SFTP reconnect flow with proper validation
- Add log.debug to all silent exception handlers in ssh_client

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

gui/app.py

@@ -171,15 +171,14 @@ class App(ctk.CTk):
         # Use provided key or default to first tab
         current_key = restore_tab_key or self._tab_keys[0]
 
-        # Save live SFTP session before destroying tabs
-        saved_sftp = self.files_tab._sftp
-        saved_sftp_path = self.files_tab._remote_path
-        saved_sftp_alias = self.files_tab._current_alias
+        # Save state before destroying tabs
+        saved_remote_path = self.files_tab._remote_path
         saved_local_path = self.files_tab._local_path
-        self.files_tab._sftp = None  # Prevent disconnect on destroy
+        had_sftp = self.files_tab._sftp is not None and self.files_tab._sftp.connected
 
-        # Disconnect terminal before destroying tabs
+        # Disconnect terminal and SFTP before destroying tabs
         self.terminal_tab._disconnect()
+        self.files_tab._disconnect_sftp()
 
         # Detach tab contents
         self.terminal_tab.pack_forget()
@@ -225,23 +224,17 @@ class App(ctk.CTk):
         except Exception:
             pass
 
-        # Restore SFTP session without reconnecting
-        if saved_sftp and saved_sftp.connected:
-            self.files_tab._sftp = saved_sftp
-            self.files_tab._current_alias = saved_sftp_alias
-            self.files_tab._remote_path = saved_sftp_path
-            self.files_tab._local_path = saved_local_path
-            self.files_tab._set_remote_buttons_state("normal")
-            self.files_tab._remote_status.configure(
-                text=t("connected_sftp").format(alias=saved_sftp_alias)
-            )
-            self.files_tab._refresh_local()
-            self.files_tab._refresh_remote()
+        # Restore file paths and reconnect properly
+        self.files_tab._local_path = saved_local_path
+        self.files_tab._refresh_local()
+        if alias and had_sftp:
+            # Had active SFTP — reconnect and restore remote path
+            self.files_tab._remote_path = saved_remote_path
+            self.files_tab.set_server(alias)
         elif alias:
-            # No live session — reconnect via server selection
             self.files_tab.set_server(alias)
 
-        # Restore server selection for other tabs
+        # Restore server selection for other tabs (terminal auto-reconnects)
         if alias:
             self.terminal_tab.set_server(alias)
             self.info_tab.set_server(alias)