community: every ledger takes its write lock, so the inbox check can no longer land on top of a friend accept

src-tauri/src/ledger.rs

@@ -63,6 +63,18 @@ mod tests {
         assert_eq!(CELL.load(Ordering::SeqCst), 2, "the second write clobbered the first");
     }
 
+    /// Why spaces::invite, spaces::remove_member and proposals::decide all
+    /// `drop(ledger)` before their tail call into open(): this lock is NOT
+    /// reentrant, so re-taking the same file in the same task is a hang, not
+    /// an error. Nothing in the compiler catches that.
+    #[tokio::test]
+    async fn the_same_file_twice_would_hang() {
+        let _first = hold("test-reentrant.json").await;
+        let again =
+            tokio::time::timeout(std::time::Duration::from_millis(200), hold("test-reentrant.json")).await;
+        assert!(again.is_err(), "a second hold on an already-held file must never be granted");
+    }
+
     /// Different files must not block each other, or dispatching sealed cargo
     /// out of a held inbox would deadlock.
     #[tokio::test]