Remove all code paths that manipulate config files without Phase 2 locking:
1. Installer: Remove ensure_allowed_nodes_file_reference() call (line 1674)
- Migration now handled exclusively by config migrate-to-file
2. Installer: Make migration failures fatal in update_allowed_nodes()
- Prevents fallback to unsafe Python manipulation
3. Daemon sanitizer: Remove os.WriteFile() call
- Now only sanitizes in-memory copy, doesn't write back to disk
- Logs warning instructing admin to run `config migrate-to-file`
4. Self-heal script: Replace 132 lines of Python with CLI call
- sanitize_allowed_nodes() now calls `config migrate-to-file`
- Eliminates uncoordinated Python-based config rewriting
All config mutations now flow exclusively through Phase 2 CLI with
atomic operations and file locking. No code paths remain that can
create duplicate allowed_nodes blocks.
Addresses Codex review feedback on Phase 2 gaps.
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