Fixes #417: When using --from-main mode (either explicitly or auto-detected), git history backfill now defaults to disabled. This prevents creating incorrect deletion records for locally-created beads that don't exist in main's git history. Changes: - Add resolveNoGitHistoryForFromMain() helper function - Apply noGitHistory=true for both explicit and auto-detected from-main mode - Add comprehensive unit tests 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: GraemeF <graeme@graemef.com> Co-Authored-By: Claude <noreply@anthropic.com>