Replaces merge-based upgrades with a two-phase approach:
1. Extract: analyzes user's fork, captures customizations as a
migration guide (intent + implementation details in markdown)
2. Upgrade: checks out clean upstream in a worktree, reapplies
customizations from the guide, validates, and swaps in
Key features:
- Tiered complexity (lightweight/standard/complex)
- Sub-agent exploration with haiku for efficient analysis
- Incremental guide updates instead of full re-extraction
- Live e2e testing via worktree symlinks before swapping
- New-changes guard prevents losing unrecorded work
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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