chore(rust): add CLAUDE.md for rust generator

generators/rust/CLAUDE.md

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+# Rust Generator
+
+This file provides guidance for Claude Code when working with the Rust generator.
+
+## Rust-Specific Requirements
+
+- **Framework compatibility**: Generated code targets modern Rust (2021 edition+) with tokio async runtime
+- **Dependencies**: Minimize dependencies; prefer serde for serialization, reqwest for HTTP
+- **Naming conventions**:
+  * Crate names and modules: snake_case
+  * Structs, enums, traits: PascalCase
+  * Functions, methods, variables: snake_case
+  * Constants: SCREAMING_SNAKE_CASE
+- **Async patterns**: Use async/await with tokio runtime for all I/O operations
+- **Error handling**: Use Result<T, E> with custom error types
+- **Formatting**: All code must pass `rustfmt` and `cargo clippy`
+
+## Key Directories
+
+### Rust Generator (generators/rust/)
+- `base/` - Base generator infrastructure (CLI, context, project management)
+- `codegen/` - Rust AST builder and code generation primitives
+- `sdk/` - Full SDK generator with HTTP client
+- `model/` - Rust type generation (structs, enums, unions)
+- `dynamic-snippets/` - Code example generation
+
+## Key Architectural Patterns
+
+**Five-Package Structure**:
+1. **base/** - Shared infrastructure (`AbstractRustGeneratorCli`, `RustProject`, `RustFilenameRegistry`)
+2. **codegen/** - AST builder (`Writer`, `Struct`, `Enum`, `Method`, etc.)
+3. **model/** - Type generation (structs, enums, unions, aliases)
+4. **sdk/** - Full SDK with HTTP client, pagination, error handling
+5. **dynamic-snippets/** - Code example generation
+
+**Filename Collision Resolution**: Priority-based registration system appends `_type` suffix to resolve conflicts (e.g., `user.rs` → `user_type.rs`). Don't bypass `RustFilenameRegistry`.
+
+**Template Variables**: Static files in `/base/src/asIs/` use placeholders like `{{PACKAGE_NAME}}`, `{{PACKAGE_VERSION}}` replaced by `RustProject.replaceTemplateVariables()`.
+
+**Dual-Generator Pattern**: SDK composes model generator via `generateModels({ context: sdkContext.toModelGeneratorContext() })` for consistency.
+
+## Development
+
+```bash
+pnpm install
+pnpm --filter @fern-api/rust-sdk compile
+pnpm --filter @fern-api/rust-model compile
+pnpm --filter @fern-api/rust-sdk dist:cli    # Build Docker CLI
+pnpm --filter @fern-api/rust-model dist:cli  # Build Docker CLI
+```
+
+### Configuration Options
+
+Configuration schema: `generators/rust/codegen/src/custom-config/RustSdkCustomConfigSchema.ts` and `RustModelCustomConfigSchema.ts`
+
+## Testing
+
+```bash
+# From repository root
+pnpm seed test --generator rust-sdk --fixture <fixture-name> --skip-scripts
+pnpm seed test --generator rust-model --fixture <fixture-name> --skip-scripts
+```
+
+When working with the Rust generator:
+- Verify generated code compiles: `cd seed/rust-sdk/<fixture> && cargo build`
+- Run generated tests: `cargo test`
+- Validate formatting: `cargo fmt --check && cargo clippy`
+- Check AST node tests with vitest snapshots: `pnpm test:update --filter @fern-api/rust-codegen`