docs(troubleshooting): add reconnect steps after host reboot

docs/reference/troubleshooting.md

@@ -143,6 +143,56 @@ $ colima status
 
 ## Runtime
 
+### Reconnect after a host reboot
+
+After a host reboot, the container runtime, OpenShell gateway, and sandbox may not be running.
+Follow these steps to reconnect.
+
+1. Start the container runtime.
+
+   - **Linux:** start Docker if it is not already running (`sudo systemctl start docker`)
+   - **macOS:** open Docker Desktop or start Colima (`colima start`)
+
+1. Check sandbox state.
+
+   ```console
+   $ openshell sandbox list
+   ```
+
+   If the sandbox shows `Ready`, skip to step 4.
+
+1. Restart the gateway (if needed).
+
+   If the sandbox is not listed or the command fails, restart the OpenShell gateway:
+
+   ```console
+   $ openshell gateway start --name nemoclaw
+   ```
+
+   Wait a few seconds, then re-check with `openshell sandbox list`.
+
+1. Reconnect.
+
+   ```console
+   $ nemoclaw <name> connect
+   ```
+
+1. Start auxiliary services (if needed).
+
+   If you use the Telegram bridge or cloudflared tunnel, start them again:
+
+   ```console
+   $ nemoclaw start
+   ```
+
+:::{admonition} If the sandbox does not recover
+:class: warning
+
+If the sandbox remains missing after restarting the gateway, run `nemoclaw onboard` to recreate it.
+The wizard prompts for confirmation before destroying an existing sandbox. If you confirm, it **destroys and recreates** the sandbox — workspace files (SOUL.md, USER.md, IDENTITY.md, AGENTS.md, MEMORY.md, and daily memory notes) are lost.
+Back up your workspace first by following the instructions at [Back Up and Restore](../workspace/backup-restore.md).
+:::
+
 ### Sandbox shows as stopped
 
 The sandbox may have been stopped or deleted.