Keep the sentence a refused tool wrote, so a finished run says why rather than tool_error

distinct_agent/harness.py

@@ -1416,6 +1416,16 @@ def _event_from_result(value: Mapping[str, Any]) -> Mapping[str, Any]:
     error = value.get("error")
     if isinstance(error, Mapping):
         event["error_code"] = str(error.get("code", "tool_error"))[:80]
+        # THE CODE ALONE SAYS NOTHING ANYBODY CAN ACT ON.
+        #
+        # The model sees the full result and can correct itself, but the run
+        # record kept only "tool_error", so a person looking at a finished run
+        # -- or at twenty benchmark runs -- could see that a tool had refused
+        # and never why. "line 7 has 4 fields where the header has 5" is a
+        # sentence somebody can fix; "tool_error" is not.
+        message = error.get("message")
+        if isinstance(message, str) and message.strip():
+            event["error_message"] = message.strip()[:300]
     output = value.get("output")
     if isinstance(output, Mapping):
         saved = output.get("artifact_saved")

tests/test_harness_makes_files.py

@@ -562,3 +562,30 @@ def test_a_finished_answer_is_not_treated_as_cut_off(tmp_path) -> None:
         tmp_path,
     )
     assert result.text == "all done"
+
+
+def test_a_refusal_keeps_the_sentence_somebody_can_act_on() -> None:
+    """"tool_error" told nobody anything; the message names the line to fix."""
+
+    from distinct_agent.harness import _event_from_result
+
+    event = _event_from_result(
+        {
+            "tool_id": "create_xlsx",
+            "version": "1",
+            "ok": False,
+            "error": {
+                "code": "skill_input_error",
+                "message": "line 7 has 4 fields where the header has 5",
+            },
+        }
+    )
+    assert event["error_code"] == "skill_input_error"
+    assert event["error_message"] == "line 7 has 4 fields where the header has 5"
+
+
+def test_a_refusal_with_no_message_is_simply_a_code() -> None:
+    from distinct_agent.harness import _event_from_result
+
+    event = _event_from_result({"tool_id": "x", "ok": False, "error": {"code": "denied"}})
+    assert "error_message" not in event