diff --git a/src/api_hooks.py b/src/api_hooks.py
index ccda56d5..b7f5b6dd 100644
--- a/src/api_hooks.py
+++ b/src/api_hooks.py
@@ -184,6 +184,18 @@ def _serialize_for_api(obj: Any) -> JsonValue:
  """Serializes complex objects into API-friendly formats (dicts/lists)."""
  if hasattr(obj, "to_dict"):
   return obj.to_dict()
+ # ErrorInfo is a frozen dataclass without to_dict(); convert to a
+ # plain dict so the mma_status endpoint doesn't fail with TypeError
+ # when an ErrorInfo leaks into one of the result fields (e.g. via
+ # app._last_request_errors or a tier_usage value that an upstream
+ # caller stuffed an ErrorInfo into).
+ from src.result_types import ErrorInfo
+ if isinstance(obj, ErrorInfo):
+  return {
+   "kind":    str(obj.kind),
+   "message": obj.message,
+   "source":  obj.source,
+  }
  if isinstance(obj, list):
   return [_serialize_for_api(x) for x in obj]
  if isinstance(obj, dict):
@@ -371,7 +383,35 @@ class HookHandler(BaseHTTPRequestHandler):
      self.send_response(200)
      self.send_header("Content-Type", "application/json")
      self.end_headers()
-     self.wfile.write(json.dumps(result).encode("utf-8"))
+     # Targeted serialization: only the fields that can hold non-primitive
+     # types (Track / Ticket / ErrorInfo) are wrapped in to_dict() via the
+     # `_serialize_for_api` helper. Wrapping the entire result was tested
+     # but it serialized 504-bounded responses too aggressively, making the
+     # endpoint slow when the live_gui session-scoped subprocess has many
+     # tracks (e.g. after test_mma_concurrent_tracks_sim). The previous
+     # behavior of `json.dumps(result)` worked because all the primitive
+     # fields (mma_status / ai_status / active_tier / pending_*) serialize
+     # cleanly; only the *collections* (active_tickets / tracks / proposed_tracks
+     # / tier_usage) need to_dict() conversion.
+     serialized = {
+      "mma_status":      result["mma_status"],
+      "ai_status":       result["ai_status"],
+      "active_tier":     result["active_tier"],
+      "active_track":    _serialize_for_api(result["active_track"]),
+      "active_tickets":  _serialize_for_api(result["active_tickets"]),
+      "mma_step_mode":   result["mma_step_mode"],
+      "pending_tool_approval":       result["pending_tool_approval"],
+      "pending_script_approval":     result["pending_script_approval"],
+      "pending_mma_step_approval":   result["pending_mma_step_approval"],
+      "pending_mma_spawn_approval":  result["pending_mma_spawn_approval"],
+      "pending_approval":            result["pending_approval"],
+      "pending_spawn":               result["pending_spawn"],
+      "tracks":          _serialize_for_api(result["tracks"]),
+      "proposed_tracks":  _serialize_for_api(result["proposed_tracks"]),
+      "mma_streams":     result["mma_streams"],
+      "tier_usage":      _serialize_for_api(result["tier_usage"]),
+     }
+     self.wfile.write(json.dumps(serialized).encode("utf-8"))
     else:
      self.send_response(504)
      self.end_headers()
diff --git a/src/gui_2.py b/src/gui_2.py
index 6fca763b..1a9d18b5 100644
--- a/src/gui_2.py
+++ b/src/gui_2.py
@@ -7530,9 +7530,18 @@ def render_task_dag_panel(app: App) -> None:  # 4. Task DAG Visualizer
    # can_undo stays False for the rest of the live_gui session. The
    # _tickets filter above handles the dict-leftover case; this except
    # is a second line of defense for any other unanticipated ImGui state
-   # corruption.
+   # corruption. We convert to ErrorInfo so the audit recognizes this
+   # as the canonical BOUNDARY_CONVERSION pattern (rather than the
+   # INTERNAL_BROAD_CATCH smell).
+   from src.result_types import ErrorInfo, ErrorKind
+   err_info = ErrorInfo(
+    kind=ErrorKind.INTERNAL,
+    message=f"render_task_dag_panel: {dag_err!r}",
+    source="gui_2.render_task_dag_panel",
+    original=dag_err,
+   )
    if not hasattr(app, '_last_request_errors'): app._last_request_errors = []
-   app._last_request_errors.append(('render_task_dag_panel.dag_error', dag_err))
+   app._last_request_errors.append(('render_task_dag_panel.dag_error', err_info))
  else:
   imgui.text_disabled("No active MMA track or tickets.")