## Summary
- keep operator-routed external checkouts out of managed worktree
preflight, cleanup, and lost-work reconciliation paths
- mark injected custom graph worktree creation as native so workspace
mode accepts the managed backend
- add an extraction regression guard for the ownership fences
## Test plan
- `pnpm --filter @fusion/engine exec vitest run
src/executor/__tests__/external-checkout-extraction-guards.test.ts
--silent=passed-only --reporter=dot`
- `pnpm --filter @fusion/engine typecheck`
- `pnpm check:changesets`
- targeted ESLint on the changed TypeScript files
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Bug Fixes**
* External execution checkouts are no longer treated as Fusion-managed
worktrees.
* Prevented unnecessary Git checks, cleanup, and reconciliation during
retries, pauses, recovery, and stuck-task handling.
* Invalid external checkout configurations now fail safely with an
error.
* Graph-injected worktrees now use the native worktree backend for
consistent setup.
* **Tests**
* Added coverage verifying external checkouts remain excluded from
managed worktree operations.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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