fix(http-server-csharp): emitter type errors

[sophia-ramsey]

Addresses errors I encountered while using the C# server emitter to emit code from the ai foundry spec for the agent contracts api service package. Includes tests

Issues addressed:

• duplicate nullable suffixes: fixed optional nullable value parameters emitting invalid C# types by ensuring nullable suffixes are applied only once (int?? to int?)
• multipart content: fixed multipart operations emitting <Unresolved Symbol ...> by falling back to the original @multipartBody metadata when canonicalization data is unavailable
• record parameter fixes: fixed error-model constructors emitting incompatible types such as Record, Array, or object instead of the same concrete structured types used by their properties
• parameter ordering fix: fixed controller calls passing positional arguments in a different order than their business-interface signatures while preserving positional syntax for existing generated code
• void as a success type: fixed void | @error responses generating invalid result assignments by excluding error branches from success-response analysis and emitting direct awaits with NoContent()

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commit: f769da2

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• ✅ @typespec/http-server-csharp

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@typespec/http-server-csharp - fix ✏️

fix errors in emitter including duplicate nullable suffixes, unresolved symbols for multipart content, incompatible types, parameter ordering, and void as a success type

[Copilot]

Pull request overview

This PR improves the C# HTTP server emitter’s correctness around nullable/optional parameter rendering, response handling for union return types (especially void | @error patterns), and controller argument ordering by tracking the original (business) operation behind each canonicalized HTTP operation.

Changes:

• Fixes “double nullable” (int??) emission for optional nullable value-type parameters across interfaces and mocks.
• Tracks canonical operation → source operation to preserve business-parameter ordering when generating controller call sites.
• Improves response analysis to emit 204 NoContent (and NoContent()) for void success unions while still handling value success unions correctly; adds multipart and error-model-related robustness tests.

Reviewed changes

Copilot reviewed 20 out of 21 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/http-server-csharp/test/snapshots/sample-service/generated/controllers/PetsController.cs	Updates generated DELETE action to return 204/NoContent for void success.
packages/http-server-csharp/test/nullable-parameters.test.ts	Adds integration-style test to prevent int??/Choice?? in emitted mocks/interfaces.
packages/http-server-csharp/src/service-resolution.ts	Returns both canonical ops map and a canonical→source operation map.
packages/http-server-csharp/src/service-resolution.test.ts	Verifies canonical→source operation tracking behavior.
packages/http-server-csharp/src/emitter.tsx	Plumbs canonical→source operation map via a new Alloy context provider.
packages/http-server-csharp/src/context/operation-source-context.ts	Introduces OperationSources context for canonical→source operation lookup.
packages/http-server-csharp/src/components/type-expression/type-expression.tsx	Adds helper to detect nullable value-type unions for correct T? emission.
packages/http-server-csharp/src/components/scaffolding/mock-implementations.tsx	Aligns mock signatures with nullable/optional rules and multipart fallback detection.
packages/http-server-csharp/src/components/render-root.tsx	Adds multipart fallback detection for interface usings when canonical metadata is absent.
packages/http-server-csharp/src/components/multipart-fallback.test.tsx	New test ensuring multipart interface + mocks stay aligned without canonicalization.
packages/http-server-csharp/src/components/models/models.tsx	Adjusts JsonNodes-using decision for root error models (includes inherited checks).
packages/http-server-csharp/src/components/models/model-helpers.ts	Improves modelNeedsJsonNodes recursion/inheritance handling.
packages/http-server-csharp/src/components/models/error-models.tsx	Uses TypeExpression for union/tuple/record/array ctor parameter typing.
packages/http-server-csharp/src/components/models/error-models.test.tsx	Adds tests for structured error constructor typing + inherited JsonNodes using.
packages/http-server-csharp/src/components/interfaces/interfaces.tsx	Fixes nullable suffix emission; adds multipart decorator fallback helpers.
packages/http-server-csharp/src/components/interfaces/interfaces.test.tsx	Adds tests for nullable suffix and multipart fallback behavior.
packages/http-server-csharp/src/components/controllers/controllers.tsx	Passes source (business) operation into ControllerAction via context lookup.
packages/http-server-csharp/src/components/controllers/controllers.test.tsx	Adds test ensuring source operation preserves positional argument order.
packages/http-server-csharp/src/components/controller-action/response-analysis.ts	Updates success-status analysis for unions (skip errors, handle void success → 204).
packages/http-server-csharp/src/components/controller-action/controller-action.tsx	Orders call arguments based on source operation; uses updated success-status analysis.
packages/http-server-csharp/src/components/controller-action/controller-action.test.tsx	Adds regression tests for void/value union handling and call-arg ordering.

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