fix: release cancelled catalog refresh leases (#453)

tests/test_available_issue_snapshot_store.py

@@ -88,3 +88,14 @@ def test_catalog_store_is_private(tmp_path):
 
     assert os.stat(path.parent).st_mode & 0o777 == 0o700
     assert os.stat(path).st_mode & 0o777 == 0o600
+
+
+def test_cancelled_refresh_releases_its_lease_for_immediate_takeover(tmp_path):
+    path = tmp_path / "available.sqlite3"
+    first = AvailableIssueSnapshotStore(path, clock=lambda: 100.0)
+    second = AvailableIssueSnapshotStore(path, clock=lambda: 100.0)
+    owner = first.try_acquire_refresh(lease_seconds=30)
+
+    first.release_refresh(owner)
+
+    assert second.try_acquire_refresh(lease_seconds=30) is not None