compact: snapshot reinjection above last summary

codex-rs/core/src/compact.rs

@@ -1660,6 +1660,22 @@ keep me updated
             },
         ];
         assert_eq!(refreshed, expected);
+
+        let refreshed_value =
+            serde_json::to_value(&refreshed).expect("serialize refreshed history");
+        let Value::Array(refreshed_items) = refreshed_value else {
+            panic!("expected refreshed history to serialize as array");
+        };
+
+        assert_snapshot!(
+            "process_compacted_history_reinject_above_last_summary_shapes",
+            context_snapshot::format_labeled_items_snapshot(
+                "When compaction output has multiple summary-only user messages and no real user message, canonical context is reinserted above the last summary.",
+                &[("Refreshed History Layout", refreshed_items.as_slice())],
+                &ContextSnapshotOptions::default()
+                    .render_mode(ContextSnapshotRenderMode::KindWithTextPrefix { max_chars: 64 }),
+            )
+        );
     }
 
     #[test]

codex-rs/core/src/snapshots/codex_core__compact__tests__process_compacted_history_reinject_above_last_summary_shapes.snap

@@ -0,0 +1,10 @@
+---
+source: core/src/compact.rs
+expression: "context_snapshot::format_labeled_items_snapshot(\"When compaction output has multiple summary-only user messages and no real user message, canonical context is reinserted above the last summary.\",\n&[(\"Refreshed History Layout\", refreshed_items.as_slice())],\n&ContextSnapshotOptions::default().render_mode(ContextSnapshotRenderMode::KindWithTextPrefix\n{ max_chars: 64 }),)"
+---
+Scenario: When compaction output has multiple summary-only user messages and no real user message, canonical context is reinserted above the last summary.
+
+## Refreshed History Layout
+00:message/user:<COMPACTION_SUMMARY>\nolder summary
+01:message/developer:fresh permissions
+02:message/user:<COMPACTION_SUMMARY>\nlatest summary