docs: comment std::process::exit(0) intent in M_UNKNOWN_TOKEN recovery

hive-matrix-mcp/src/client.rs

@@ -84,6 +84,12 @@ pub async fn build_and_restore(
                         "failed to remove sdk state dir; next startup may fail with stale state"
                     );
                 }
+                // Exit 0 rather than returning Err: `hive-matrix-daemon` is a
+                // single-purpose process binary; the call site is before any
+                // tasks are spawned so there are no resources to clean up.
+                // Using exit(0) (not Err) keeps systemd's Restart=on-failure
+                // from looping — the systemd.paths watcher re-launches us
+                // once hive-c0re writes a fresh token file.
                 std::process::exit(0);
             }
             return Err(e);