Problem

When running bd migrate sync <branch-name>, the sync branch is created from the current HEAD, which includes the entire codebase. This results in:

• Wasted space: ~50MB+ of stale source code sitting in the sync branch
• Confusion: The branch looks like a code branch but only .beads/ is ever updated
• Inconsistency with similar patterns: gh-pages branches typically only contain build output, not source code

Example after running bd migrate sync beads-sync:

beads-sync branch contains:
├── .beads/          ← only this gets updated
├── apps/            ← stale, never updated
├── packages/        ← stale, never updated
├── src/             ← stale, never updated
└── ... 60+ other dirs/files (all stale)

Proposed Solution

Add a --clean or --orphan flag to create a minimal sync branch:

bd migrate sync beads-sync --clean

This would:

1. Create an orphan branch (no parent commits)
2. Only include .beads/ directory
3. Result in a clean, minimal sync branch

Alternative

Automatically use the orphan approach by default (with --full flag to preserve current behavior if needed).

Environment

• bd version: 0.47.1
• OS: macOS (Darwin)