## ADDED Requirements

### Requirement: Modular CLI Core
The `rusty-claude-cli` application SHALL be structured into multiple distinct modules (`cli`, `config`, `execution`, `permissions`, `diagnostics`, `ui`) instead of a single monolithic `main.rs` file.

#### Scenario: Unchanged Application Behavior
- **WHEN** the application is compiled and executed
- **THEN** all CLI commands, arguments, and interactive features function exactly as they did before the refactoring.

#### Scenario: Unchanged Test Suite
- **WHEN** `cargo test` is run for the `rusty-claude-cli` crate
- **THEN** all existing unit and integration tests pass successfully.

#### Scenario: Code Compilation
- **WHEN** `cargo check` is run
- **THEN** the crate compiles without any new warnings or errors related to module structure or unresolved imports.

#### Scenario: Code Formatting
- **WHEN** `cargo fmt --all` is run
- **THEN** the new module structure complies with the project's formatting standards.