## Summary
- add an explicit API route that persists one clean external Git
checkout for task execution and enforced review
- fence execution to the checkout's persisted branch and fail closed
when the route becomes invalid
- allow completion invariants to validate explicitly routed checkouts
outside the project worktree directory
## Test plan
- `pnpm --filter @fusion/engine exec vitest run
src/__tests__/external-execution-checkout.test.ts
src/__tests__/review-checkout.test.ts
src/__tests__/engine-no-blocking-shellout.test.ts --silent=passed-only
--reporter=dot`
- `pnpm --filter @fusion/engine exec vitest run
src/__tests__/executor-fast-mode-workflows.test.ts -t 'prepares a
persisted external execution checkout' --silent=passed-only
--reporter=dot`
- `FUSION_DASHBOARD_DEEP=1 pnpm --filter @fusion/dashboard exec vitest
run src/__tests__/routes-tasks-near-duplicate.test.ts -t 'PATCH
external-checkout' --project dashboard-api --silent=passed-only
--reporter=dot`
- `pnpm --filter @fusion/engine typecheck`
- `pnpm --filter @fusion/dashboard exec tsc --noEmit`
- `pnpm verify:fast`
- `pnpm test:gate` (605 non-PostgreSQL tests pass; local PostgreSQL
suites cannot authenticate because the configured client returns an
empty password)
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Added support for routing task execution and review through
operator-selected external Git checkouts.
* External checkouts are validated for valid Git repositories, attached
branches, clean status, and branch consistency.
* Tasks can clear previously configured external checkout routing.
* Valid routed checkouts are used directly without creating a separate
worktree.
* **Bug Fixes**
* Invalid, incomplete, dirty, or mismatched checkout configurations now
fail early with clear validation errors.
* Missing tasks return the appropriate not-found response.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Co-authored-by: gsxdsm <gsxdsm@users.noreply.github.com>
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