[chrischeng-c4]

Closes #34

Summary of Changes

Implements the first slice of #34 for crates/openapi-codegen:

• crates/openapi-codegen/src/domain/emit/rust/models_emit.rs:
  • Added is_string_enum to identify component schemas eligible for Rust enum generation (type: string, non-empty all-string enum, empty properties/unions).
  • Added emit_enum to emit #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)] pub enum Name { ... } with #[serde(rename = "<value>")] on each variant and PascalCase variant names via to_pascal, preserving declared order.
  • Implemented deterministic disambiguation using NameRegistry for colliding variant names (e.g. FooBar, FooBar_2) and non-identifier values ("" -> Anonymous, "123" -> _123, "self" -> Self_).
  • Preserved existing behavior for untyped, non-string, and inline enums, which continue mapping to String.
• crates/openapi-codegen/src/domain/emit/rust/rsmap.rs:
  • Added unit test asserting that inline string enums, non-string enums, and nullable inline enums remain String / Option<String>.
• crates/openapi-codegen/src/domain/emit/rust.rs:
  • Added integration unit test emits_string_enum_component_model verifying models.rs generation for string enum component schemas with struct $ref.

Local Validation Results

1. Cancelled Broad Package Test:

   • Earlier unconstrained cargo test --locked -p openapi-codegen hung on background network TLS test domain::emit::py::tests::tls_alpn::generated_python_h2_runtime_negotiates_tls_alpn_h2 and was terminated via supported manage_task(Action=kill) per local testing policy (Task 0297a583-9bab-44e1-a787-5e6e80d8ff75/task-96). This broad package test is NOT RUN locally and left to cloud CI.

2. Affected Isolated Unit Tests (PASSED):

   • cargo test --locked -p openapi-codegen --lib domain::emit::rust (19 passed, 0 failed):
     • declared_order: passed
     • rename_non_identifier_values: passed
     • collision_disambiguation: passed
     • nullable_enum_emits_same_enum: passed
     • struct_property_refs_enum: passed
     • non_string_enum_left_as_string: passed
     • serde_round_trip_rejects_undeclared_value: passed
     • inline_and_non_string_enums_stay_string: passed
     • emits_string_enum_component_model: passed
     • All 10 existing Rust emitter unit tests passed.
   • Unaffected TS and IR unit tests:
     • domain::emit::ts (27 passed)
     • domain::emit::py::models_emit (1 passed)
     • domain::emit::py::pymap (1 passed)
     • domain::ir (14 passed)

3. Negative Control:

   • Reverting emit_schema to the type-alias branch caused exactly the 6 new enum test rows to fail while all other rows passed.

4. Formatting:

   • cargo fmt --check -p openapi-codegen passed cleanly.

Cloud CI Requirements

• Cloud MR Checks: Unfiltered package tests, server/network/h2c integration suites, and cross-language profile gates belong in cloud CI.
• Status: PENDING / NOT RUN locally awaiting authorized cloud CI execution on the opened PR.