Make Generated Conv Method Internal if Parameter Type is Internal

[jorgerangel-msft]

If a generated convenience method has a parameter whose type is internal, the generated convenience method should be made internal if the enclosing type is not already, to avoid a compilation error. This can occur if a type was customized to be internal via client.tsp or through custom code.

[github-actions]

🎯 Issue Triage

When a generated convenience method has a parameter whose type is internal (e.g., customized via client.tsp or custom code), the method should also be made internal to avoid a C# compilation error due to accessibility mismatch.

Category: Bug
Area: emitter:client:csharp

⚠️ No reproduction provided. A minimal repro would help diagnose this issue.

🔍 Analysis

• Affected component: C# client emitter (@typespec/http-client-csharp) — convenience method generation
• Root cause: The emitter does not propagate the internal accessibility of a parameter type to the enclosing generated convenience method. In C#, a public method cannot expose an internal type in its signature without a compilation error.
• Trigger: This occurs when a type is customized to be internal via client.tsp or via custom code (partial class overrides), and that type ends up as a parameter of a generated convenience method on a public client.
• Fix direction: The code generator should check the accessibility of parameter types when generating convenience methods and, if any parameter type is internal, downgrade the generated method's accessibility to internal (unless the enclosing type is already internal).

📝 Suggested next steps

• Add a test case in the C# emitter test suite: a model customized to internal used as a parameter in an operation, verify the generated convenience method is internal.
• Identify the code path in the C# generator that emits convenience method accessibility and apply the accessibility propagation logic.
• Verify the fix does not affect cases where the enclosing client type is already internal.

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