## Summary
- recover task-ID-pinned worktrees when their directory remains but Git
metadata/registration is gone
- preserve the orphan directory under `.fusion/recovery/worktrees`
before recreating the worktree
- retain existing fail-closed behavior for active, foreign, repo-root,
or out-of-root paths
## Problem
A task-pinned worktree can lose `.git` metadata while leaving build
artifacts behind. Fusion classifies that path as incomplete or
unregistered, but then calls `git worktree remove --force`. Git cannot
remove a directory it no longer recognizes as a worktree, so acquisition
aborts and the scheduler can repeat the same recovery indefinitely.
The observed reproduction left `.build` and `.swiftpm` under the pinned
path after Git registration was gone.
## Fix
For an inactive path that is both:
1. inside the configured worktree root, and
2. classified as incomplete or unregistered,
hold the shared worktree-path reservation across classification,
preservation, and recreation. Recovery directories are created one
canonical, project-contained component at a time, then the orphan is
atomically moved into `.fusion/recovery/worktrees` and the pinned
worktree is recreated. Moving rather than deleting preserves any unknown
task artifacts for operator inspection. Other classifications continue
through the existing guarded Git-removal path.
## Verification
- `pnpm --filter @fusion/engine exec vitest run
src/__tests__/worktree-acquisition.test.ts --silent=passed-only
--reporter=dot` — 30 passed
- `pnpm --filter @fusion/engine typecheck`
- `pnpm --filter @fusion/engine build`
- `pnpm test:gate:static`
- `pnpm check:changesets`
- `git diff --check`
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
- **Bug Fixes**
- Improved recovery of task-pinned worktrees when incomplete or stale
directories occupy the expected location.
- Preserves eligible inactive or unregistered worktree contents in a
recovery area instead of deleting them.
- Prevents unsafe recovery through symbolic links and handles concurrent
recovery attempts reliably.
- Supports recovery when directories span different storage devices.
- Ensures interrupted or invalid worktree states can be recreated safely
without disrupting active sessions.
- **Documentation**
- Added a patch changeset documenting the improved worktree recovery
behavior.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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