Implement Spector integration tests for azure/client-generator-core/client-default-value

[Copilot]

Adds Spector integration test coverage for the @clientDefaultValue decorator scenarios, and fixes an emitter bug discovered in the process.

Emitter fix: header params with clientDefaultValue

Optional header parameters with @clientDefaultValue were wrapped in an options?.param !== undefined guard, which prevented the default from ever being sent when the caller omits the option. Since the paramMap already includes a ?? default fallback, the guard is unnecessary and incorrect.

Before (broken):

headers: {
  ...(options?.customHeader !== undefined
    ? { "custom-header": options?.customHeader ?? "application/json" }
    : {}),
}

After (fixed):

headers: {
  "custom-header": options?.customHeader ?? "application/json",
}

The fix is in buildHeaderParameter() in operationHelpers.ts: skip the undefined conditional when the parameter has a type-matching clientDefaultValue. This mirrors how query/path parameters with defaults are already handled.

New test coverage

• Added azure/client-generator-core/client-default-value to azureModularTsps in cadl-ranch-list.js
• Generated client and scaffolding (tspconfig.yaml, .gitignore, src/index.d.ts)
• Created azureClientGeneratorCoreClientDefaultValue.spec.ts covering all four scenarios:
  • putModelProperty — model property defaults (timeout, tier, retry) returned by server
  • getOperationParameter — query param defaults (pageSize=10, format=json) auto-applied
  • getPathParameter — path parameter with explicit default value
  • getHeaderParameter — header defaults (accept, x-custom-header) auto-applied without caller input
• Updated clientDefaultValue.md unit test snapshot to match corrected header emission
• Updated @typespec/http-specs and @azure-tools/azure-http-specs to latest dev versions

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