refactor: clarify error format resolution

Co-authored-by: fuxingloh <4266087+fuxingloh@users.noreply.github.com>

Author: Copilot

packages/use-agently/src/bin.ts

@@ -7,10 +7,15 @@ import { handleCliError } from "./errors.js";
 
 installTelemetry(cli);
 
+function resolveOutputFormat(): "tui" | "json" {
+  const opts = cli.optsWithGlobals?.();
+  if (opts?.output === "tui" || opts?.output === "json") return opts.output;
+  return process.stderr.isTTY ? "tui" : "json";
+}
+
 try {
   await cli.parseAsync();
   await Promise.all([checkAutoUpdate(), flushTelemetry()]);
 } catch (err) {
-  const format = (cli.optsWithGlobals?.().output ?? (process.stderr.isTTY ? "tui" : "json")) as "tui" | "json";
-  handleCliError(err, format);
+  handleCliError(err, resolveOutputFormat());
 }

packages/use-agently/src/errors.test.ts

@@ -22,20 +22,23 @@ describe("handleCliError", () => {
 
   test("prints json error when format is json", () => {
     expect(() => handleCliError(new Error("boom"), "json")).toThrow("exit:1");
+    expect(exitSpy).toHaveBeenCalledWith(1);
     expect(errorSpy).toHaveBeenCalledWith(JSON.stringify({ error: { message: "boom" } }));
   });
 
   test("prints plain text when format is tui and stderr is not a TTY", () => {
     Object.defineProperty(process.stderr, "isTTY", { value: false, configurable: true });
 
     expect(() => handleCliError(new Error("oops"), "tui")).toThrow("exit:1");
+    expect(exitSpy).toHaveBeenCalledWith(1);
     expect(errorSpy).toHaveBeenCalledWith("Error: oops");
   });
 
   test("prints boxed error when format is tui and stderr is a TTY", () => {
     Object.defineProperty(process.stderr, "isTTY", { value: true, configurable: true });
 
     expect(() => handleCliError(new Error("boxed"), "tui")).toThrow("exit:1");
+    expect(exitSpy).toHaveBeenCalledWith(1);
     const output = errorSpy.mock.calls.map((c) => c[0]).join("");
     expect(output).toContain("boxed");
     expect(output).toContain("Error");