[Bug]: http-server-csharp: tsp compile fails with error: Visibility of property 'name' is sealed and cannot be changed.

[abatishchev]

Describe the bug

Full error message:

node_modules/@azure-tools/typespec-azure-resource-manager/lib/models.tsp:88:1 - error visibility-sealed: Visibility of property 'name' is sealed and cannot be changed.
> 88 | @armResourceInternal(Properties)

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
    emit-mocks: none
    overwrite: true

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

When using @typespec/http-server-csharp as an emitter against an ARM RP TypeSpec project, compilation fails with a visibility-sealed error originating in @azure-tools/typespec-azure-resource-manager/lib/models.tsp. The error indicates the emitter (or its processing) is attempting to modify the visibility of a sealed property name.

Category: Bug

Area: emitter:service:csharp

⚠️ No TypeSpec reproduction code provided. A minimal repro (standalone .tsp file triggering the issue without relying on a full ARM RP project) would help diagnose this.

🔍 Analysis

• The error visibility-sealed fires at line 88 of @azure-tools/typespec-azure-resource-manager/lib/models.tsp, inside the @armResourceInternal decorator call.
• This suggests that @typespec/http-server-csharp triggers a code path that attempts to mutate or re-evaluate visibility on a property (name) that has already been sealed by the ARM library.
• This may be a compatibility issue between the visibility-sealing behavior introduced in the compiler and how http-server-csharp processes ARM resource models.
• The error does not occur unless @typespec/http-server-csharp is added as an emitter, implying the emitter (or an option it enables) triggers the problematic code path.

📝 Suggested next steps

• Identify the version of @typespec/http-server-csharp and @azure-tools/typespec-azure-resource-manager in use.
• Check whether this reproduces on the latest versions of both packages.
• Investigate whether http-server-csharp applies visibility transformations on ARM resource properties that conflict with sealed visibility.
• Provide a minimal .tsp repro if possible to isolate the issue from the full ARM RP project setup.

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