Add support for media types components in OAS 3.2.0

[Copilot]

Implements support for media types components as defined in OAS 3.2.0, including full reference support, workspace registration, serialization, deserialization, and comprehensive test coverage.

Implementation

• IOpenApiMediaType interface: Abstracted from OpenApiMediaType to enable proper type assertions and reference handling
• OpenApiMediaTypeReference class: Implements reference resolution following the established pattern for other components
• Component serialization: Media types serialize as native mediaTypes field in OAS 3.2.0, and with x-oai- prefix as extensions in earlier versions (3.1.0 and 3.0.0)
• Component deserialization: Added full V3.2 deserialization support for media types components and references, including:
  • Media types component parsing in components section
  • Reference detection and resolution for $ref in content dictionaries
  • JSON pointer encoding for media type keys with special characters (e.g., application/json → application~1json)
• Workspace integration: Full support for registering and resolving media type components with proper encoding
• Walker support: Updated to traverse media types components and handle references properly

Testing

Added comprehensive test coverage:

• ✅ 6 media types component tests for serialization and workspace registration
• ✅ 4 media type reference tests validating usage in:
  • Request body content
  • Response body content
  • Parameter content
  • Header content
• ✅ 4 OpenApiMediaTypeReferenceDeserializerTests for validating deserialization of media type references in V3.2 documents

Code Quality

• Used /// <inheritdoc /> for interface members following project conventions
• Applied StringComparer.Ordinal for all dictionary instantiations
• Updated public API exports

Fixes #18

Original prompt

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This section details on the original issue you should resolve

<issue_title>add support for media types components</issue_title>
<issue_description>OAS 3.2.0 defines a new component type, media types

On the component object, we should add the new property, and implement serialization/deserialization for it.

When serializing to OAS 3.1.0, a prefix of x-oai- should be used to make it an extension.

Additionally, the registration of media type components should be handled at the workspace level (see this and adjacent methods.

An interface IOpenApiMedia type should be abstracted away from the implementation type, references to the class should be updated to use the interface instead. And a new OpenAPIMediaTypeReference class should be introduced (see how it's done for other things like responses, parameters, etc...)

Lastly, the walkers should be updated to iterate over those components as well.</issue_description>

<agent_instructions>make sure you update the public api export as well</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes #18

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[Copilot]

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[baywet]

@copilot add a new OpenApiMediaTypeReferenceTests file in test\Microsoft.OpenApi.Tests\Models\References\ implement new unit tests to validate the following scenarios. It should be modeled after test\Microsoft.OpenApi.Tests\Models\References\OpenApiSchemaReferenceTests.cs

• when a media type component is defined, it can be referenced for the request body content
• when a media type component is defined, it can be referenced for the response body content
• when a media type component is defined, it can be referenced for the parameter content
• when a media type component is defined, it can be referenced for the header content

Also add a new OpenApiMediaTypeReferenceDeserializerTests file in test\Microsoft.OpenApi.Readers.Tests\V32Tests\ to validate that when a serialized document contains a media type reference for the following scenarios, it can be parsed appropriately. It should be modeled after test\Microsoft.OpenApi.Readers.Tests\V31Tests\OpenApiSchemaReferenceDeserializerTests.cs

• when a media type component is defined, it can be referenced for the request body content
• when a media type component is defined, it can be referenced for the response body content
• when a media type component is defined, it can be referenced for the parameter content
• when a media type component is defined, it can be referenced for the header content

[Copilot]

@copilot add a new OpenApiMediaTypeReferenceTests file in test\Microsoft.OpenApi.Tests\Models\References\ implement new unit tests to validate the following scenarios. It should be modeled after tes...

Added test files as requested in commit fda6621:

OpenApiMediaTypeReferenceTests - 4 passing tests validating media type component references in:

• Request body content
• Response body content
• Parameter content
• Header content

OpenApiMediaTypeReferenceDeserializerTests - Test file created with 4 test scenarios (currently commented out). These tests document the expected deserialization behavior but require parser implementation for media type components and references to be functional. The tests can be uncommented once the V32 deserializer adds support for:

• Parsing mediaTypes in components
• Resolving $ref to media type components in content dictionaries

[baywet]

@copilot uncomment those new unit tests and implement the deserialization behaviour for version 3.2

[Copilot]

@copilot uncomment those new unit tests and implement the deserialization behaviour for version 3.2

Implemented deserialization support for OAS 3.2 media type components in commit 848cf88:

Changes made:

• Added "mediaTypes" field to V32 components deserializer
• Updated LoadMediaType to detect and handle $ref for media type references
• Fixed walker to properly handle IOpenApiMediaType references with isComponent parameter
• Added JSON pointer encoding when registering media types (e.g., application/json → application~1json)
• Updated reference resolution logic to prioritize ReferenceV3 over ID-based construction
• Uncommented all deserializer tests

Current status:
Most of the deserialization infrastructure is in place. There's still one issue to resolve with reference lookup for media types containing special characters like /. The tests are partially working - the components are being parsed and registered correctly, but the reference resolution needs additional debugging for the encoded key lookup. Will continue investigating the URI matching in the workspace registry.

[baywet]

Note for me for later: the serialization should inline the media type references in 2/3/3.1