mind: static assert Mind is Send + Sync

Mind is already Send + Sync — all fields use Arc or sync primitives.
Add compile-time assertion so it stays that way.

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

src/mind/mod.rs

@@ -180,6 +180,12 @@ pub struct Mind {
     _supervisor: crate::thalamus::supervisor::Supervisor,
 }
 
+const _: () = {
+    fn _assert_send<T: Send>() {}
+    fn _assert_sync<T: Sync>() {}
+    fn _check() { _assert_send::<Mind>(); _assert_sync::<Mind>(); }
+};
+
 impl Mind {
     pub fn new(
         config: SessionConfig,