## Summary
- restore explicit executor guidance for assigning workflows to tasks
the agent creates
- keep the existing prohibition on rerouting the task currently being
executed
- restore parity between both built-in executor prompt variants and
their regression test
## Test plan
- `pnpm --filter @fusion/core exec vitest run --silent=passed-only
--reporter=dot src/__tests__/agent-prompts.test.ts`
- `pnpm --filter @fusion/core typecheck`
- `pnpm check:changesets`
- `pnpm exec eslint packages/core/src/agents/agent-prompts.ts`
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Improvements**
* Executor workflow guidance now appears only when task creation or
delegation capabilities are available.
* Built-in executor prompts provide clearer task-assignment instructions
based on available capabilities.
* Custom executor prompts remain unchanged.
* Removed outdated workflow-setting guidance when task-management
capabilities are unavailable.
* **Tests**
* Added coverage for task creation, delegation, and capability-specific
workflow guidance scenarios.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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