# Invariant Doc Entity
### Scope
- **Purpose**: Define behavioral contracts that must always hold for this crate.
- **Responsibility**: Master index for all invariant doc instances in this crate.
- **In Scope**: Instance 001 — architectural boundary between `cli_fmt` and `strs_tools`.
- **Out of Scope**: Desired behavior and processing logic — see `feature/` instances.
### Overview Table
| 001 | [Architectural Boundary](001_architectural_boundary.md) | cli_fmt vs strs_tools separation boundary | ✅ |