Fix http-server-csharp crash on interfaces with template operations

[Copilot]

• Understand root cause: interfaceDeclarationOperations in service.ts doesn't filter template operations, causing TemplateParameter types to be passed to emitType
• Add isTemplateDeclaration(operation) guard in interfaceDeclarationOperations loop
• Add TemplateParameter guard in #resolveOperationResponse as a safety net (with comment)
• Add regression test: verifies template operations are skipped and non-template operations work
• Add changeset entry (updated description per review feedback)
• Merged latest changes from main

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Bug]: Unable to emit @typespec/http-server-csharp using azure-rest-api-specs typespec</issue_title>
<issue_description>### Describe the bug

Considering the PR and branch containerregistry-conversion, I run into issues when trying to compile typespec with emit option "@typespec/http-server-csharp".

Log:

> tsp compile specs/containerregistry/main.tsp

TypeSpec compiler v1.4.0

✔ Compiling
✔ @azure-tools/typespec-autorest 819ms specs/containerregistry/
× Running @typespec/http-server-csharp...
Emitter "@typespec/http-server-csharp" crashed! This is a bug.
Please file an issue at https://github.com/microsoft/typespec/issues

Error: Encountered type TemplateParameter which we don't know how to emit.
    at compilerAssert (file:///C:/work/acr/dev/src/ACR.RP/ACR.RP.Web.Spec/node_modules/@typespec/compiler/dist/src/core/diagnostics.js:150:11)
    at typeEmitterKey (file:///C:/work/acr/dev/src/ACR.RP/ACR.RP.Web.Spec/node_modules/@typespec/asset-emitter/dist/src/asset-emitter.js:618:17)
    at Object.emitType (file:///C:/work/acr/dev/src/ACR.RP/ACR.RP.Web.Spec/node_modules/@typespec/asset-emitter/dist/src/asset-emitter.js:238:25)
    at #resolveOperationResponse (file:///C:/work/acr/dev/src/ACR.RP/ACR.RP.Web.Spec/node_modules/@typespec/http-server-csharp/dist/src/lib/service.js:744:26)
    at CSharpCodeEmitter.interfaceDeclarationOperations (file:///C:/work/acr/dev/src/ACR.RP/ACR.RP.Web.Spec/node_modules/@typespec/http-server-csharp/dist/src/lib/service.js:586:77)
    at file:///C:/work/acr/dev/src/ACR.RP/ACR.RP.Web.Spec/node_modules/@typespec/asset-emitter/dist/src/asset-emitter.js:376:55
    at withTypeContext (file:///C:/work/acr/dev/src/ACR.RP/ACR.RP.Web.Spec/node_modules/@typespec/asset-emitter/dist/src/asset-emitter.js:519:9)
    at invokeTypeEmitter (file:///C:/work/acr/dev/src/ACR.RP/ACR.RP.Web.Spec/node_modules/@typespec/asset-emitter/dist/src/asset-emitter.js:366:9)
    at Object.emitInterfaceOperations (file:///C:/work/acr/dev/src/ACR.RP/ACR.RP.Web.Spec/node_modules/@typespec/asset-emitter/dist/src/asset-emitter.js:327:20)
    at CSharpCodeEmitter.interfaceDeclaration (file:///C:/work/acr/dev/src/ACR.RP/ACR.RP.Web.Spec/node_modules/@typespec/http-server-csharp/dist/src/lib/service.js:542:22)

--------------------------------------------------
Library Version                0.58.0-alpha.20
TypeSpec Compiler Version      1.4.0
--------------------------------------------------

My configuration looks as follows:

emit:
  - "@azure-tools/typespec-autorest"
  - "@typespec/http-server-csharp"
options:
  ...
  "@typespec/http-server-csharp":
    emitter-output-dir: "{project-root}/typespec/codegen"
    output-type: "models"
    collection-type: "enumerable"

Surprised, considering that emitter "@azure-tools/typespec-autorest" works as expected, and also used the "@typespec/openapi3" to further verify, and it works as expected. But for some reason, the csharp generator runs into an issue.

Reproduction

The description is pretty straightforward.
I will go ahead and create a fork so you may clone and reproduce locally, and update the thread.

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.</issue_description>

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

• Fixes [Bug]: Unable to emit @typespec/http-server-csharp using azure-rest-api-specs typespec #8500

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[markcowl]

@copilot please pull the latest changes from main

[Copilot]

@copilot please pull the latest changes from main

Done — merged latest from main in 578f446.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/http-server-csharp@9894

commit: add0d2e

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-server-csharp

Show changes

@typespec/http-server-csharp - fix ✏️

Fix crash when emitting interfaces that contain template operations. Template operations (e.g. getItem<T>(): T) within interfaces will simply be skipped when emitting the interface.

[azure-sdk]

You can try these changes here

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