fix: OpenAPI generator now correctly handles REST endpoints with single complex parameter

[xerial]

For REST endpoints (non-RPC) with a single non-primitive body parameter (unary endpoint calls),
the OpenAPI request body schema now directly references the parameter type instead of wrapping
it in an object with properties. This makes the OpenAPI spec consistent with how the server
actually handles requests - the request body is mapped directly to the parameter.

This fix aligns the OpenAPI generator behavior with:

• HttpRequestMapper which maps the entire request body to a single parameter for REST endpoints
• HttpClientIR which generates client code that passes the parameter directly for unary calls

[gemini-code-assist]

Summary of Changes

Hello @xerial, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an inconsistency in the OpenAPI generator where REST endpoints with a single complex body parameter were incorrectly represented. The fix ensures that the generated OpenAPI schema accurately reflects the expected request body structure, improving the fidelity of the API documentation and client code generation.

Highlights

• OpenAPI Schema Generation Fix: The OpenAPI generator now correctly handles REST endpoints that accept a single, non-primitive body parameter. Previously, the schema for such endpoints would incorrectly wrap the parameter type within an object.
• Direct Parameter Type Referencing: For these 'unary endpoint calls' (REST, single non-primitive parameter), the OpenAPI request body schema now directly references the parameter's type, aligning with how the server processes requests.
• Consistency with Server and Client: This change ensures the generated OpenAPI specification is consistent with HttpRequestMapper (server-side request handling) and HttpClientIR (client-side code generation), which both expect the parameter directly.
• Updated Test Cases: Test cases for OpenAPI generation have been updated to reflect the new, correct schema output for unary endpoint calls, specifically for the /v1/post5 endpoint.

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[gemini-code-assist]

Code Review

This pull request correctly adjusts the OpenAPI generator to handle REST endpoints with a single complex parameter. Instead of wrapping the parameter in an object, the schema now directly references the parameter's type, which aligns with the server's behavior. The logic change is sound and is supported by corresponding test updates. I've added one suggestion to refactor the logic for detecting this specific case to be more concise and idiomatic using Scala's pattern matching.

[gemini-code-assist]

The logic to determine isUnaryEndpointCall can be simplified and made more idiomatic using pattern matching on httpClientCallInputs. This would make the intent clearer by directly checking for a single, non-primitive parameter, and removes the need for the intermediate primitiveOnlyInputs variable.

Suggested change

	val primitiveOnlyInputs =
	routeAnalysis.httpClientCallInputs.nonEmpty && routeAnalysis.httpClientCallInputs.forall(x =>
	isPrimitive(x.surface)
	)
	val isUnaryEndpointCall =
	!route.isRPC && routeAnalysis.httpClientCallInputs.size == 1 && !primitiveOnlyInputs
	val isUnaryEndpointCall = !route.isRPC && (routeAnalysis.httpClientCallInputs match {
	case Seq(p) => !isPrimitive(p.surface)
	case _ => false
	})