- Merge _init_persistent_shell + _start_persistent_shell into single method
- Move execute() dispatcher and cleanup() into PersistentShellMixin
so LocalEnvironment and SSHEnvironment inherit them
- Remove broad except Exception wrappers from _execute_oneshot in both backends
- Replace try/except with os.path.exists checks in local _read_temp_files
and _cleanup_temp_files
- Remove redundant bash -c from SSH oneshot (SSH already runs in a shell)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>