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.
