## Implementation
- [x] Repair the accidentally overwritten project note to the state it would have had after an append.
- [x] Add behavior tests for append-by-default and explicit replacement.
- [x] Implement `replace_file` on summary file-write tools and workflow rules writes.
- [x] Update agent tool descriptions and instructions.
- [x] Run focused tests.
- [x] Run `dotnet test MeetingAssistant.slnx`.
- [x] Run `openspec validate append-file-write-tools-by-default --strict`.