fix: separate mapped type from explicit properties in generated response object type

[Copilot]

TypeScript prohibits mixing explicit properties and a mapped type in the same object literal. When an OpenAPI spec includes a default response alongside explicit status codes, the generator was emitting invalid TypeScript:

// ❌ Before — TypeScript error: mapped type cannot be combined with explicit properties
ResponseBuilderFactory<{
  200: { ... };
  400: { ... };
  [statusCode in Exclude<HttpStatusCode, 200 | 400>]: { ... };
}>

// ✅ After — intersection separates the two
ResponseBuilderFactory<{
  200: { ... };
  400: { ... };
} & {
  [statusCode in Exclude<HttpStatusCode, 200 | 400>]: { ... };
}>

Summary

Generated response types broke tsc when an operation defined both explicit status codes and a default response.

• responses-type-coder.ts: buildResponseObjectType now partitions entries into explicit (numeric) and mapped ([statusCode in ...]) buckets. When both are present, emits an intersection; otherwise emits a single object as before.
• responses-type-coder.test.ts: Three new buildResponseObjectType tests cover the intersection path, the explicit-only path, and the mapped-only path.
• Snapshots updated: 5 Jest snapshots in operation-type-coder.test.ts (×4) and generate.test.ts (×1) updated to match the new intersection output format.

Original Prompt

TypeScript doesn't like this:

export type addPet_$_v3 = OmitValueWhenNever<{
  ...
  response: ResponseBuilderFactory<{
    200: { ... };
    400: { ... };
    422: { ... };
    [statusCode in Exclude<HttpStatusCode, 200 | 400 | 422>]: { ... };
  }>;
  ...
}>;

Manual acceptance tests

• Generate types from a spec that has both explicit status codes and a default response (e.g. Petstore); confirm the emitted .types.ts file compiles without TypeScript errors
• Spec with only explicit status codes (no default) generates a single object type with no & intersection
• Spec with only a default response generates [statusCode in HttpStatusCode]: ... with no intersection
• Previously broken type (with 200, 400, 422, and default) compiles cleanly under tsc --noEmit

Tasks

• Partition buildResponseObjectType entries into explicit vs. mapped buckets; emit intersection when both present
• Add three unit tests covering intersection, explicit-only, and mapped-only cases
• Update 5 affected Jest snapshots to match new intersection output
• Add changeset (patch)

[pmcelhaney]

@copilot unit tests are failing

[Copilot]

@copilot unit tests are failing

Fixed in 798f439 — the snapshot tests in operation-type-coder.test.ts (×4) and generate.test.ts (×1) needed to be updated to match the new intersection output format.