fix(client): include the detail in client error messages (#50929)

packages/cli/test/mini.test.ts

@@ -221,7 +221,7 @@ describe("mini command", () => {
       expect(JSON.parse(result.stdout)).toMatchObject({
         type: "error",
         sessionID: "",
-        error: { type: "unknown", message: "UnexpectedStatus" },
+        error: { type: "unknown", message: "UnexpectedStatus: 500" },
       })
     } finally {
       server.stop(true)

packages/client/src/promise/generated/client-error.ts

@@ -9,8 +9,9 @@ export class ClientError extends Error {
   override readonly name = "ClientError"
   constructor(
     readonly reason: ClientErrorReason,
-    options?: ErrorOptions,
+    options?: ErrorOptions & { readonly detail?: string | null },
   ) {
-    super(reason, options)
+    const detail = options?.detail ?? (options?.cause instanceof Error ? options.cause.message : undefined)
+    super(detail ? `${reason}: ${detail}` : reason, options)
   }
 }

packages/client/src/promise/generated/client.ts

@@ -335,7 +335,7 @@ export function make(options: ClientOptions) {
     try {
       await response.body?.cancel()
     } catch {}
-    throw new ClientError("UnexpectedStatus", { cause: { status: response.status } })
+    throw new ClientError("UnexpectedStatus", { cause: { status: response.status }, detail: String(response.status) })
   }
 
   const request = async <A>(descriptor: RequestDescriptor, requestOptions?: RequestOptions): Promise<A> => {
@@ -359,7 +359,7 @@ export function make(options: ClientOptions) {
         try {
           await response.body?.cancel()
         } catch {}
-        throw new ClientError("UnsupportedContentType")
+        throw new ClientError("UnsupportedContentType", { detail: response.headers.get("content-type") })
       }
       if (response.body === null) throw new ClientError("MalformedResponse")
       const reader = response.body.getReader()
@@ -2185,7 +2185,7 @@ async function json(response: Response): Promise<unknown> {
     try {
       await response.body?.cancel()
     } catch {}
-    throw new ClientError("UnsupportedContentType")
+    throw new ClientError("UnsupportedContentType", { detail: response.headers.get("content-type") })
   }
   let text: string
   try {

packages/client/test/promise.test.ts

@@ -191,6 +191,27 @@ test("declared errors with a data envelope read the nested message", async () =>
   expect(error).toMatchObject({ name: "WorktreeError", data: { message: "Worktree directory unavailable" } })
 })
 
+test("client errors keep the reason and describe the failure in the message", async () => {
+  const failure = (fetch: () => Promise<Response>) =>
+    OpenCode.make({ baseUrl: "http://localhost:3000", fetch })
+      .session.list()
+      .catch((cause: unknown) => cause)
+  expect(await failure(() => Promise.reject(new TypeError("Unable to connect")))).toMatchObject({
+    reason: "Transport",
+    message: "Transport: Unable to connect",
+  })
+  expect(await failure(async () => new Response("", { status: 500 }))).toMatchObject({
+    reason: "UnexpectedStatus",
+    message: "UnexpectedStatus: 500",
+  })
+  expect(await failure(async () => new Response("<html>", { headers: { "content-type": "text/html" } }))).toMatchObject(
+    {
+      reason: "UnsupportedContentType",
+      message: "UnsupportedContentType: text/html",
+    },
+  )
+})
+
 test("project.update uses the global project contract", async () => {
   let request: Request | undefined
   const project = {