Generate typed HTTP error responses

[adamcavendish]

Summary

• Split generated operation responses into success-only return types and typed HTTP error surfaces across Rust, Go, Python, TypeScript Fetch, Java, and Kotlin
• Preserve operation-specific error classification by OpenAPI response entry, including exact status, wildcard range, default, and unexpected non-2xx responses
• Keep status, headers, raw bodies, and lazy/deferred typed body access available on generated HTTP errors
• Add a typed HTTP error fixture, cross-language goldens, and runtime tests for HTTP error behavior

Why

Generated clients previously surfaced documented 4xx/5xx responses through the normal success path. That made an HTTP failure look like a successful operation result and allowed callers to accidentally treat failed creates as success. This changes generated semantics so normal returns mean HTTP success only.

Validation

• cargo test --workspace --all-targets --quiet
• cargo test --test typed_http_error_runtime -- --nocapture
• cargo test --test jvm_http_error_runtime -- --nocapture
• cargo test --test multipart_runtime_smoke -- --nocapture
• UPDATE_GOLDEN=1 cargo test --test golden_tests_java_okhttp
• UPDATE_GOLDEN=1 cargo test --test golden_tests_typescript_fetch
• Golden tests for Go, Python httpx/requests, Rust reqwest/ureq/aioduct, Java, Kotlin, and TypeScript Fetch
• Golden build scripts for Go, Python httpx/requests, Rust reqwest/ureq/aioduct, Java, Kotlin, and TypeScript Fetch
• cargo fmt --all -- --check
• git diff HEAD^ --check

[codecov]

Codecov Report

❌ Patch coverage is 91.96607% with 161 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/generators/python/httpx/emit_api.rs	85.86%	40 Missing ⚠️
src/generators/python/requests/emit_api.rs	85.86%	40 Missing ⚠️
src/generators/typescript/fetch/sigil_emit_api.rs	89.53%	25 Missing ⚠️
src/generators/rust/common/emit_api.rs	92.03%	16 Missing ⚠️
src/generators/go/http/sigil_emit_api.rs	95.87%	9 Missing ⚠️
src/generators/response_names.rs	73.52%	9 Missing ⚠️
src/generators/java/okhttp/sigil_emit.rs	78.37%	8 Missing ⚠️
src/generators/java/okhttp/sigil_emit_api.rs	98.01%	7 Missing ⚠️
src/generators/kotlin/okhttp/sigil_emit_api.rs	97.71%	6 Missing ⚠️
src/generators/rust/aioduct/sigil_emit_api.rs	96.15%	1 Missing ⚠️

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