General review waves 1-2: sweep_expired savepoint scope fix (M-1), coverage adds (arg_opt_i64, StopToken Debug), review report (docs/reviews/)

alkstore/src/value_type_tests.rs

@@ -153,6 +153,14 @@ fn stop_token_independent_tokens_do_not_flip_each_other() {
     assert!(!b.is_cancelled());
 }
 
+#[test]
+fn stop_token_debug_shows_cancelled_state() {
+    let token = StopToken::new();
+    assert!(format!("{token:?}").contains("cancelled: false"));
+    token.cancel();
+    assert!(format!("{token:?}").contains("cancelled: true"));
+}
+
 #[test]
 fn wake_carries_only_the_channel() {
     let w = Wake {