file_tools.py creates its own Docker sandbox when read_file/search_files
runs before any terminal command. The container_config was missing
docker_volumes, so the sandbox had no user volume mounts — breaking
access to heartbeat state, cron output, and all other mounted data.
Matches the existing pattern in terminal_tool.py:872.
Missed in original PR #158 (feat: add docker_volumes config).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>