fix(cli): a Windows render no longer prints taskkill's already-exited message (#6698)

* fix(cli): a Windows render no longer prints taskkill's already-exited message

* fix(cli): fold the taskkill note into the hidden() doc comment

packages/cli/src/utils/hideChildConsoles.test.ts

@@ -65,6 +65,15 @@ describe("hideChildConsoles", () => {
     expect(calls[3]?.at(-1)).toBe(callback);
   });
 
+  it("silences taskkill's stderr when its target is already gone", () => {
+    const calls = run("win32", (m) => {
+      m.execSync("taskkill /pid 1 /T /F");
+      m.execSync("echo hi");
+    });
+    expect(calls[0]?.[2]).toEqual({ windowsHide: true, stdio: "ignore" });
+    expect(calls[1]?.[2]).toEqual({ windowsHide: true });
+  });
+
   it("leaves a caller that wants the window alone", () => {
     const calls = run("win32", (m) =>
       m.spawn("browser", [], { windowsHide: false, detached: true }),

packages/cli/src/utils/hideChildConsoles.ts

@@ -7,15 +7,18 @@ type ChildProcessModule = Record<string, unknown>;
 
 const ENTRY_POINTS = ["spawn", "spawnSync", "exec", "execSync", "execFile", "execFileSync", "fork"];
 
-/** The call's arguments with `windowsHide: true` set unless the caller chose either way. */
+/** The call's arguments with `windowsHide: true` unless the caller chose; a taskkill's stderr is dropped too. */
 function hidden(command: string, rest: unknown[]): unknown[] {
+  const defaults = /^taskkill\s/i.test(command)
+    ? { windowsHide: true, stdio: "ignore" }
+    : { windowsHide: true };
   const args = [...rest];
   const at = args.findIndex((arg) => arg && typeof arg === "object" && !Array.isArray(arg));
   if (at >= 0) {
-    args[at] = { windowsHide: true, ...(args[at] as object) };
+    args[at] = { ...defaults, ...(args[at] as object) };
   } else {
     const callback = args.findIndex((arg) => typeof arg === "function");
-    args.splice(callback < 0 ? args.length : callback, 0, { windowsHide: true });
+    args.splice(callback < 0 ? args.length : callback, 0, defaults);
   }
   return [command, ...args];
 }