fix(core): improve headless mode detection for flags and query args (#18855)

packages/core/src/utils/headless.test.ts

@@ -99,16 +99,50 @@ describe('isHeadlessMode', () => {
     expect(isHeadlessMode({ prompt: true })).toBe(true);
   });
 
-  it('should return false if query is provided but it is still a TTY', () => {
-    // Note: per current logic, query alone doesn't force headless if TTY
-    // This matches the existing behavior in packages/cli/src/config/config.ts
-    expect(isHeadlessMode({ query: 'test query' })).toBe(false);
+  it('should return true if query is provided', () => {
+    expect(isHeadlessMode({ query: 'test query' })).toBe(true);
+  });
+
+  it('should return true if -p or --prompt is in process.argv as a fallback', () => {
+    const originalArgv = process.argv;
+    process.argv = ['node', 'index.js', '-p', 'hello'];
+    try {
+      expect(isHeadlessMode()).toBe(true);
+    } finally {
+      process.argv = originalArgv;
+    }
+
+    process.argv = ['node', 'index.js', '--prompt', 'hello'];
+    try {
+      expect(isHeadlessMode()).toBe(true);
+    } finally {
+      process.argv = originalArgv;
+    }
+  });
+
+  it('should return true if -y or --yolo is in process.argv as a fallback', () => {
+    const originalArgv = process.argv;
+    process.argv = ['node', 'index.js', '-y'];
+    try {
+      expect(isHeadlessMode()).toBe(true);
+    } finally {
+      process.argv = originalArgv;
+    }
+
+    process.argv = ['node', 'index.js', '--yolo'];
+    try {
+      expect(isHeadlessMode()).toBe(true);
+    } finally {
+      process.argv = originalArgv;
+    }
   });
 
   it('should handle undefined process.stdout gracefully', () => {
     const originalStdout = process.stdout;
-    // @ts-expect-error - testing edge case
-    delete process.stdout;
+    Object.defineProperty(process, 'stdout', {
+      value: undefined,
+      configurable: true,
+    });
 
     try {
       expect(isHeadlessMode()).toBe(false);
@@ -122,8 +156,10 @@ describe('isHeadlessMode', () => {
 
   it('should handle undefined process.stdin gracefully', () => {
     const originalStdin = process.stdin;
-    // @ts-expect-error - testing edge case
-    delete process.stdin;
+    Object.defineProperty(process, 'stdin', {
+      value: undefined,
+      configurable: true,
+    });
 
     try {
       expect(isHeadlessMode()).toBe(false);

packages/core/src/utils/headless.ts

@@ -28,18 +28,25 @@ export interface HeadlessModeOptions {
  * @returns true if the environment is considered headless.
  */
 export function isHeadlessMode(options?: HeadlessModeOptions): boolean {
-  if (process.env['GEMINI_CLI_INTEGRATION_TEST'] === 'true') {
-    return (
-      !!options?.prompt ||
-      (!!process.stdin && !process.stdin.isTTY) ||
-      (!!process.stdout && !process.stdout.isTTY)
-    );
+  if (process.env['GEMINI_CLI_INTEGRATION_TEST'] !== 'true') {
+    const isCI =
+      process.env['CI'] === 'true' || process.env['GITHUB_ACTIONS'] === 'true';
+    if (isCI) {
+      return true;
+    }
   }
-  return (
-    process.env['CI'] === 'true' ||
-    process.env['GITHUB_ACTIONS'] === 'true' ||
-    !!options?.prompt ||
+
+  const isNotTTY =
     (!!process.stdin && !process.stdin.isTTY) ||
-    (!!process.stdout && !process.stdout.isTTY)
+    (!!process.stdout && !process.stdout.isTTY);
+
+  if (isNotTTY || !!options?.prompt || !!options?.query) {
+    return true;
+  }
+
+  // Fallback: check process.argv for flags that imply headless or auto-approve mode.
+  return process.argv.some(
+    (arg) =>
+      arg === '-p' || arg === '--prompt' || arg === '-y' || arg === '--yolo',
   );
 }