docs: add reconnection and error recovery docs

docs/DEBUG.md

@@ -58,3 +58,26 @@ openssl rsa -in key.pem -check -noout
 - Verify server address and port
 - Check firewall allows outbound TCP/UDP to port 64738
 - Test with: `nc -zv <host> 64738`
+
+### Connection drops / reconnection
+
+When tuimble loses connection, it retries automatically with backoff.
+The chatlog shows each attempt:
+
+```
+✗ disconnected from server
+reconnecting in 2s (attempt 1/10)...
+✗ attempt 1: network error: [Errno 111] Connection refused
+reconnecting in 4s (attempt 2/10)...
+✓ connected as myname
+```
+
+Common causes:
+
+- **Server restart** — normal, reconnect succeeds when server is back
+- **Network loss** — check connectivity, tuimble retries automatically
+- **Auth timeout** — server may drop idle connections; reconnect handles this
+- **"rejected" with no retry** — wrong password or certificate issue
+
+If reconnection fails after 10 attempts, press `F5` to retry manually.
+Update `config.toml` if server details changed.