fix(agent): set tool_name on tool-result messages at construction time

Introduces make_tool_result_message() in tool_dispatch_helpers.py as the
single place where tool-result message dicts are built. All six construction
sites in tool_executor.py, agent_runtime_helpers.py, and mini_swe_runner.py
now use it, so tool_name is set in memory from the moment a message is
created rather than relying on fallback logic in the flush paths.

Fixes blank tool_name in both state.db and JSON session logs.

Adds tests.

mini_swe_runner.py

@@ -38,6 +38,7 @@ from typing import List, Dict, Any, Optional, Literal
 
 import fire
 from dotenv import load_dotenv
+from agent.tool_dispatch_helpers import make_tool_result_message
 
 # Load environment variables
 load_dotenv()
@@ -536,11 +537,9 @@ Complete the user's task step by step."""
                             completed = True
                         
                         # Add tool response
-                        messages.append({
-                            "role": "tool",
-                            "content": result_json,
-                            "tool_call_id": tc.id
-                        })
+                        messages.append(make_tool_result_message(
+                            tc.function.name, result_json, tc.id,
+                        ))
                         
                         print(f"   ✅ exit_code={result['exit_code']}, output={len(result['output'])} chars")