fix(copilot): honor advertised model endpoints (#34958)

packages/llm/src/providers/github-copilot.ts

@@ -12,10 +12,12 @@ export const id = ProviderID.make("github-copilot")
 export type ModelOptions = Omit<RouteDefaultsInput, "providerOptions"> &
   ProviderAuthOption<"optional"> & {
     readonly baseURL: string
+    readonly endpoint?: "chat" | "responses"
     readonly providerOptions?: OpenAIProviderOptionsInput
   }
 
-export const shouldUseResponsesApi = (modelID: string | ModelID) => {
+export const shouldUseResponsesApi = (modelID: string | ModelID, endpoint?: ModelOptions["endpoint"]) => {
+  if (endpoint) return endpoint === "responses"
   const model = String(modelID)
   const match = /^gpt-(\d+)/.exec(model)
   if (!match) return false
@@ -28,7 +30,7 @@ const chatRoute = OpenAIChat.route.with({ provider: id })
 const responsesRoute = OpenAIResponses.route.with({ provider: id })
 
 const defaults = (options: ModelOptions) => {
-  const { apiKey: _, auth: _auth, baseURL: _baseURL, ...rest } = options
+  const { apiKey: _, auth: _auth, baseURL: _baseURL, endpoint: _endpoint, ...rest } = options
   return rest
 }
 
@@ -53,7 +55,8 @@ export const configure = (options: ModelOptions) => {
     chatRoute.with(withOpenAIOptions(modelID, defaults(options))).model({ id: modelID })
   return {
     id,
-    model: (modelID: string | ModelID) => (shouldUseResponsesApi(modelID) ? responses(modelID) : chat(modelID)),
+    model: (modelID: string | ModelID) =>
+      shouldUseResponsesApi(modelID, options.endpoint) ? responses(modelID) : chat(modelID),
     responses,
     chat,
     configure,

packages/llm/test/exports.test.ts

@@ -50,6 +50,20 @@ describe("public exports", () => {
     expect(
       GitHubCopilot.configure({ baseURL: "https://api.githubcopilot.test", apiKey: "fixture" }).model,
     ).toBeFunction()
+    expect(
+      GitHubCopilot.configure({
+        baseURL: "https://api.githubcopilot.test",
+        apiKey: "fixture",
+        endpoint: "responses",
+      }).model("mai-code-1-flash-picker").route.id,
+    ).toBe("openai-responses")
+    expect(
+      GitHubCopilot.configure({
+        baseURL: "https://api.githubcopilot.test",
+        apiKey: "fixture",
+        endpoint: "chat",
+      }).model("gpt-5").route.id,
+    ).toBe("openai-chat")
   })
 
   test("protocol barrels expose supported low-level routes", () => {