[Bug]: http-server-csharp: Some generated classes have wrong name, include _2

[abatishchev]

Describe the bug

The generated Operations controller has a wrong class name: it includes _2 and doesn't match the ctor.

Some examples:

public partial class ErrorResponse_2 : HttpServiceException
{
    public ErrorResponse(ErrorDetail error = default)
    {
        // ...
    }

and

public partial class OperationsController_2 : ControllerBase
{
    public OperationsController(IOperations_2 operations)
    {
         // ..
    }
}

Also:

public interface IOperations_2
{
}

Reproduction

1. Use an ARM RP typespec
2. Add the following to tspconfig.yaml

emit:
  - "@typespec/http-server-csharp"
options:
  "@typespec/http-server-csharp":
    emitter-output-dir: "{project-root}/generated/{emitter-name}"
    output-type: all

Checklist

• Follow our Code of Conduct
• Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion.
• The provided reproduction is a minimal reproducible example of the bug.

[github-actions]

🎯 Issue Triage

The @typespec/http-server-csharp emitter generates C# class/interface names with an incorrect _2 suffix (e.g., OperationsController_2, IOperations_2, ErrorResponse_2), while constructors use the correct names — causing a mismatch.

Category: Bug
Area: emitter:service:csharp

⚠️ No playground link applicable (C# server emitter, not a TypeSpec playground issue). Reproduction requires an ARM RP TypeSpec project with the @typespec/http-server-csharp emitter configured.

🔍 Analysis

• The _2 suffix on generated class and interface names suggests a name collision resolution mechanism is incorrectly triggering — possibly when the emitter encounters duplicate type names across namespaces or versioned types.
• Affected generated artifacts: controller classes (e.g., OperationsController_2), exception classes (e.g., ErrorResponse_2), and interfaces (e.g., IOperations_2).
• The constructor names remain correct (no _2), indicating the renaming is applied only to the class/interface declaration, not consistently throughout the generated code.
• Likely root cause: name deduplication logic in the C# server emitter is appending _2 to disambiguate types that share a name, but is not updating all usages (ctors, references) consistently — or is wrongly triggering for types that don't actually conflict.
• Reproduces with ARM RP TypeSpec specs using output-type: all.

📝 Suggested next steps

• Investigate the name generation/deduplication logic in packages/http-server-csharp that appends numeric suffixes
• Check if Operations or ErrorResponse types appear in multiple namespaces (e.g., common ARM types) causing false conflicts
• Ensure the suffix is applied consistently to all references (class name, ctor, interface references) or not at all
• Add a regression test with an ARM-style TypeSpec spec

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