[yagruda]

Issue number: closes #8581

Summary

Changes

• In OpenAPIRequestValidationMiddleware:
  • Added sequence parameter handling in _normalize_multi_params and _process_model_param to convert single string values into single-item lists (and split comma strings if unparsed), ensuring sequence headers like list[str] validate consistently across HTTP API, Function URL, ALB, and VPC Lattice.
  • Allowed scalar header parameters to be joined via _restore_scalar_parameter by removing the multi-value exclusion for headers, aligning with RFC 9110 Section 5.3 where multiple header lines are equivalent to a comma-separated list.
  • Updated _get_body to extract the media type without parameters, compare case-insensitively, and accept +json media types (such as application/problem+json and application/vnd.api+json).
• Updated test_native_repeated_parameters_keep_existing_behavior in test_openapi_comma_parameters.py and added regression test cases in test_openapi_validation_middleware.py.

User experience

• Declaring a route header like x_country: Annotated[list[str], Header(alias="x-country")] accepts single values on all resolvers (e.g. x-country: US) instead of failing with 422 list_type on HTTP API / Function URL / ALB.
• Repeated header lines for a scalar string parameter (e.g. in multiValueHeaders) are joined into a comma-delimited string consistently across REST and HTTP API resolvers instead of raising 422 string_type.
• Valid requests with Content-Type: Application/JSON or application/problem+json are parsed as JSON rather than rejected with 415.

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Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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