Records the file mtime at load time; before write_config() fires, re-checks
it. If it changed (e.g. `claude mcp add`, a second BCC window, or Claude
itself writing ~/.claude.json), StaleDialog prompts with the changed top-level
key names and a masked server-section diff. "Merge & save" applies the user's
in-memory server edits on top of the current on-disk file (preserving external
non-server changes); "Overwrite anyway" proceeds as before.
- bcc_core: config_mtime(), external_change_summary(), _server_sections()
helper extracted from backup_diff for reuse
- bcc.py: StaleDialog, MainWindow._loaded_mtime tracked through load/save
- tests: 7 new tests (config_mtime, external_change_summary variants, AC merge test)
Closes#4
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
AJ