Preserve union variant docs in OpenAPI response descriptions

.chronus/changes/copilot-openapi-emitter-respect-return-type-doc-2026-7-28-13-0-55.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http"
+---
+
+Respect docs on union variants used as HTTP responses

packages/http/src/responses.ts

@@ -78,7 +78,11 @@ function resolveResponseVariants(
       continue;
     }
     // Recursively resolve nested unions
-    const resolved = resolveResponseVariants(program, option.type, unionDescription);
+    const resolved = resolveResponseVariants(
+      program,
+      option.type,
+      getDoc(program, option) ?? unionDescription,
+    );
     for (const variant of resolved) {
       if (isPlainResponseBody(program, variant.type)) {
         plainVariants.push(variant.type);

packages/openapi3/test/response-descriptions.test.ts

@@ -87,6 +87,22 @@ worksFor(supportedVersions, ({ openApiFor }) => {
     strictEqual(res.paths["/"].get.responses["409"].description, "Foo");
   });
 
+  it("uses union variant descriptions", async () => {
+    const res = await openApiFor(
+      `
+      model PetCreated { @statusCode code: 201 }
+      model PetAccepted { @statusCode code: 202 }
+      union CreatedResponses {
+        @doc("Pet Created") created: PetCreated,
+        @doc("Pet Accepted") accepted: PetAccepted,
+      }
+      op created(): CreatedResponses;
+      `,
+    );
+    strictEqual(res.paths["/"].get.responses["201"].description, "Pet Created");
+    strictEqual(res.paths["/"].get.responses["202"].description, "Pet Accepted");
+  });
+
   it("recursively expands deeply nested unions", async () => {
     const res = await openApiFor(
       `