fix(sensor): record the message of a failed Copilot tool's error

Sensor/adr_sensor/parsers/copilot_parser.py

@@ -299,7 +299,7 @@ def _process_event(self, event: Dict[str, Any], session_data: Dict[str, Any]):
             if tool is not None:
                 success = bool(data.get("success"))
                 result_text = self._normalize_tool_result(data.get("result"))
-                error_text = self._normalize_tool_result(data.get("error"))
+                error_text = self._normalize_tool_error(data.get("error"))
                 tool["result"] = result_text
                 tool["status"] = "success" if success else "error"
                 if not success:
@@ -513,6 +513,14 @@ def _normalize_tool_result(self, result: Any) -> Optional[str]:
 
         return truncate_middle(text, max_length=MAX_STRING_LENGTH, edge_chars=EDGE_CHARS)
 
+    def _normalize_tool_error(self, error: Any) -> Optional[str]:
+        """Use the message of Copilot's {"message", "code"} error object."""
+        if isinstance(error, dict):
+            message = error.get("message")
+            if isinstance(message, str) and message:
+                return truncate_middle(message, max_length=MAX_STRING_LENGTH, edge_chars=EDGE_CHARS)
+        return self._normalize_tool_result(error)
+
     def _truncate_large_arguments(self, arguments: Dict[str, Any]) -> Dict[str, Any]:
         """Truncate large string values within tool argument dictionaries."""
         if not isinstance(arguments, dict):

Sensor/tests/test_parsers.py

@@ -1680,6 +1680,33 @@ def test_tool_failure_uses_error_field_when_result_is_absent(self, tmp_path):
         assert tool.result is None
         assert tool.error == "File not found"
 
+    def test_tool_failure_uses_message_of_error_object(self, tmp_path):
+        """Copilot's schema records a failed tool's error as {"message", "code"}."""
+        session_dir = tmp_path / "error-object"
+        events = self._minimal_events("error-object") + [
+            {
+                "type": "tool.execution_start",
+                "timestamp": "2026-08-10T10:00:02.000Z",
+                "data": {"toolCallId": "call-1", "toolName": "bash", "arguments": {"command": "rm -rf build"}},
+            },
+            {
+                "type": "tool.execution_complete",
+                "timestamp": "2026-08-10T10:00:03.000Z",
+                "data": {
+                    "toolCallId": "call-1",
+                    "success": False,
+                    "error": {"message": "The user rejected this tool call.", "code": "denied"},
+                },
+            },
+        ]
+        self._write_events(session_dir, events)
+
+        entry = CopilotParser(base_path=tmp_path).parse_session_dir(session_dir)
+
+        tool = [tool for message in entry.chat_history for tool in message.tools][0]
+        assert tool.status == "error"
+        assert tool.error == "The user rejected this tool call."
+
     def test_default_max_age_days(self):
         assert CopilotParser().max_age_days == 14