Fix: Use client.apiVersions as source of truth for API version enum generation

packages/http-client-csharp/emitter/src/lib/client-model-builder.ts

@@ -5,7 +5,6 @@ import {
   SdkClientType,
   SdkEnumType,
   SdkHttpOperation,
-  UsageFlags,
 } from "@azure-tools/typespec-client-generator-core";
 import { CSharpEmitterContext } from "../sdk-context.js";
 import { CodeModel } from "../type/code-model.js";
@@ -14,11 +13,7 @@ import { fromSdkClients } from "./client-converter.js";
 import { fromSdkNamespaces } from "./namespace-converter.js";
 import { processServiceAuthentication } from "./service-authentication.js";
 import { fromSdkType } from "./type-converter.js";
-import {
-  containsMultiServiceClient,
-  firstLetterToUpperCase,
-  getClientNamespaceString,
-} from "./utils.js";
+import { firstLetterToUpperCase, getClientNamespaceString } from "./utils.js";
 
 /**
  * Creates the code model from the SDK context.
@@ -75,15 +70,7 @@ function parseApiVersions(
   enums: SdkEnumType[],
   rootClients: SdkClientType<SdkHttpOperation>[],
 ): string[] {
-  if (containsMultiServiceClient(rootClients)) {
-    return rootClients[0]?.apiVersions ?? [];
-  }
-
-  const apiVersionEnum = enums.find((e) => (e.usage & UsageFlags.ApiVersionEnum) !== 0);
-  if (apiVersionEnum) {
-    return apiVersionEnum.values.map((v) => v.value as string);
-  }
-
+  // Always use client.apiVersions as the source of truth.
   return rootClients[0]?.apiVersions ?? [];
 }
 

packages/http-client-csharp/emitter/test/Unit/client-model-builder.test.ts

@@ -440,4 +440,68 @@ describe("parseApiVersions", () => {
     ok(barClient.apiVersions.includes("bv1"), "Bar client should include bv1");
     ok(barClient.apiVersions.includes("bv2"), "Bar client should include bv2");
   });
+
+  it("should include all API versions from @versioned enum", async () => {
+    const program = await typeSpecCompile(
+      `
+      @service(#{
+        title: "Test Service",
+      })
+      @versioned(Versions)
+      namespace TestService;
+
+      enum Versions {
+        v1: "v1",
+        v2: "v2",
+        v3: "v3",
+      }
+
+      @route("/test")
+      op test(): void;
+      `,
+      runner,
+      { IsNamespaceNeeded: false },
+    );
+    const context = createEmitterContext(program);
+    const sdkContext = await createCSharpSdkContext(context);
+    const root = createModel(sdkContext);
+
+    // Verify all three versions are present in the root apiVersions
+    strictEqual(root.apiVersions.length, 3, "Should have 3 apiVersions");
+    ok(root.apiVersions.includes("v1"), "Should include v1");
+    ok(root.apiVersions.includes("v2"), "Should include v2");
+    ok(root.apiVersions.includes("v3"), "Should include v3");
+  });
+
+  it("should preserve version order from TCGC", async () => {
+    const program = await typeSpecCompile(
+      `
+      @service(#{
+        title: "Test Service",
+      })
+      @versioned(Versions)
+      namespace TestService;
+
+      enum Versions {
+        "2023-01-01",
+        "2024-01-01",
+        "2025-01-01",
+      }
+
+      @route("/test")
+      op test(): void;
+      `,
+      runner,
+      { IsNamespaceNeeded: false },
+    );
+    const context = createEmitterContext(program);
+    const sdkContext = await createCSharpSdkContext(context);
+    const root = createModel(sdkContext);
+
+    // Verify versions are in the order TCGC provides them
+    strictEqual(root.apiVersions.length, 3, "Should have 3 apiVersions");
+    strictEqual(root.apiVersions[0], "2023-01-01", "First version should be 2023-01-01");
+    strictEqual(root.apiVersions[1], "2024-01-01", "Second version should be 2024-01-01");
+    strictEqual(root.apiVersions[2], "2025-01-01", "Third version should be 2025-01-01");
+  });
 });