fix(http-server-csharp): resolve declared service namespace

[sophia-ramsey]

This pull request updates the logic for determining the generated C# service namespace in the @typespec/http-server-csharp package. Now, the namespace explicitly declared with @service is always used for the generated C# service namespace, even if an imported or unrelated namespace appears first. The changes also refactor and clarify related code, and add new tests to ensure correct behavior.

Service namespace resolution improvements:

• Added a new function getServiceNamespace in service-discovery.ts to reliably select the namespace declared with @service, falling back to the first non-standard namespace with content if no service is declared.
• Updated getServiceNamespaceName to use the new getServiceNamespace logic, ensuring the correct namespace is used for C# code generation.
• Refactored resolveServiceTypes in service-resolution.ts to use getServiceNamespace instead of the previous custom logic, and updated documentation/comments for clarity. [1] [2]

Testing and documentation:

• Added and updated tests in service-resolution.test.ts to verify that the namespace declared with @service is used, and to cover fallback behavior when no service is declared. [1] [2]
• Added a changelog entry describing the fix and its effect on generated C# service namespaces. (.chronus/changes/http-server-csharp-service-namespace-2026-09-08.md)

[pkg-pr-new]

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npm i https://pkg.pr.new/@typespec/http-server-csharp@11908

commit: 2094f03

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-server-csharp

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@typespec/http-server-csharp - fix ✏️

Use the namespace declared with @service as the generated C# service namespace, even when an imported or unrelated namespace is encountered first.

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[Copilot]

🟢 Approval recommended

The new namespace-resolution behavior is implemented via a single shared helper, has targeted test coverage for both the @service and no-service fallback paths, and includes an appropriate .chronus fix entry.

Pull request overview

This PR fixes service namespace selection in @typespec/http-server-csharp so the generated C# root namespace always comes from the namespace explicitly decorated with @service, rather than whichever non-std namespace happens to appear first. This aligns emitted C# namespaces with author intent and stabilizes output when imported/unrelated namespaces exist.

Changes:

• Added getServiceNamespace(program) to centralize “service namespace (preferred) / standalone fallback” resolution logic.
• Updated resolveServiceTypes and getServiceNamespaceName to use the unified service namespace resolution.
• Added/updated tests to lock in correct @service precedence and fallback behavior; updated a legacy generation test expectation accordingly.

File summaries

File	Description
packages/http-server-csharp/test/generation.test.ts	Updates legacy generation assertions to reflect corrected namespace qualification in emitted C# when service namespace is resolved reliably.
packages/http-server-csharp/src/service-resolution.ts	Switches service namespace discovery to the new getServiceNamespace(program) helper.
packages/http-server-csharp/src/service-resolution.test.ts	Adds coverage for preferring the @service namespace and validates standalone fallback behavior.
packages/http-server-csharp/src/service-discovery.ts	Introduces getServiceNamespace and refactors getServiceNamespaceName to use compiler getNamespaceFullName.
.chronus/changes/http-server-csharp-service-namespace-2026-09-08.md	Adds a fix changelog entry describing the user-visible namespace resolution correction.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 0
• Review effort level: Lite

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