diagnostics: full traceback in gen_error

app.py

@@ -182,7 +182,9 @@ def _safe_generate(model, kwargs):
             model.generate(**kwargs)
         _state["gen_error"] = None
     except Exception as e:
-        _state["gen_error"] = "%s: %s" % (type(e).__name__, str(e)[:400])
+        # keep the full stack — a bare "AttributeError:" tells us nothing about where it came from
+        _state["gen_error"] = ("%s: %s\n--- traceback ---\n%s"
+                               % (type(e).__name__, str(e)[:200], traceback.format_exc()[-1500:]))
         traceback.print_exc()
     finally:
         try: