diff --git a/crates/core/src/lib.rs b/crates/core/src/lib.rs
index 4aa569b4..97cf1c7f 100644
--- a/crates/core/src/lib.rs
+++ b/crates/core/src/lib.rs
@@ -1263,7 +1263,7 @@ impl Runtime {
                 .await;
             self.hooks
                 .emit(HookEvent::GenericEventFrame {
-                    frame: error_frame.clone(),
+                    frame: Box::new(error_frame.clone()),
                 })
                 .await;
             return Ok(json!({
@@ -1300,7 +1300,7 @@ impl Runtime {
             if let Some(frame) = maybe_approval_frame {
                 self.hooks
                     .emit(HookEvent::GenericEventFrame {
-                        frame: frame.clone(),
+                        frame: Box::new(frame.clone()),
                     })
                     .await;
                 events.push(event_frame_payload(&frame));
@@ -1324,7 +1324,7 @@ impl Runtime {
         };
         self.hooks
             .emit(HookEvent::GenericEventFrame {
-                frame: start_frame.clone(),
+                frame: Box::new(start_frame.clone()),
             })
             .await;
         self.hooks
@@ -1348,7 +1348,7 @@ impl Runtime {
                 };
                 self.hooks
                     .emit(HookEvent::GenericEventFrame {
-                        frame: result_frame.clone(),
+                        frame: Box::new(result_frame.clone()),
                     })
                     .await;
                 self.hooks
@@ -1380,7 +1380,7 @@ impl Runtime {
                 };
                 self.hooks
                     .emit(HookEvent::GenericEventFrame {
-                        frame: error_frame.clone(),
+                        frame: Box::new(error_frame.clone()),
                     })
                     .await;
                 self.hooks
@@ -1426,18 +1426,18 @@ impl Runtime {
             };
             self.hooks
                 .emit(HookEvent::GenericEventFrame {
-                    frame: EventFrame::McpStartupUpdate {
+                    frame: Box::new(EventFrame::McpStartupUpdate {
                         update: codewhale_protocol::McpStartupUpdateEvent {
                             server_name: update.server_name,
                             status,
                         },
-                    },
+                    }),
                 })
                 .await;
         }
         self.hooks
             .emit(HookEvent::GenericEventFrame {
-                frame: EventFrame::McpStartupComplete {
+                frame: Box::new(EventFrame::McpStartupComplete {
                     summary: codewhale_protocol::McpStartupCompleteEvent {
                         ready: summary.ready.clone(),
                         failed: summary
@@ -1450,7 +1450,7 @@ impl Runtime {
                             .collect(),
                         cancelled: summary.cancelled.clone(),
                     },
-                },
+                }),
             })
             .await;
         summary
diff --git a/crates/hooks/src/lib.rs b/crates/hooks/src/lib.rs
index d28525be..872d6c9c 100644
--- a/crates/hooks/src/lib.rs
+++ b/crates/hooks/src/lib.rs
@@ -73,7 +73,7 @@ pub enum HookEvent {
     /// mapping it to a more specific variant.
     GenericEventFrame {
         /// The raw event frame to forward.
-        frame: EventFrame,
+        frame: Box<EventFrame>,
     },
 }
 
@@ -334,6 +334,21 @@ mod tests {
         assert_eq!(encoded["payload"]["exit_code"], 0);
     }
 
+    #[test]
+    fn generic_event_frame_serialization_is_unchanged_by_boxing() {
+        let event = HookEvent::GenericEventFrame {
+            frame: Box::new(EventFrame::ResponseStart {
+                response_id: "resp-1".to_string(),
+            }),
+        };
+
+        let encoded = event.to_json();
+
+        assert_eq!(encoded["type"], "generic_event_frame");
+        assert_eq!(encoded["frame"]["event"], "response_start");
+        assert_eq!(encoded["frame"]["response_id"], "resp-1");
+    }
+
     #[tokio::test]
     async fn jsonl_sink_creates_parent_dir_and_appends_events() {
         let root = unique_temp_dir("jsonl_sink");