fix(cli): Add delimiter before printing tool response in non-interactive mode (#11351)

packages/cli/src/ui/utils/__snapshots__/textOutput.test.ts.snap

@@ -0,0 +1,23 @@
+// Vitest Snapshot v1, https://vitest.dev/guide/snapshot.html
+
+exports[`TextOutput > should correctly handle ANSI escape codes when determining line breaks 1`] = `
+"hello
+world
+next"
+`;
+
+exports[`TextOutput > should handle ANSI codes that do not end with a newline 1`] = `
+"hello
+world"
+`;
+
+exports[`TextOutput > should handle a sequence of calls correctly 1`] = `
+"first
+second part
+third"
+`;
+
+exports[`TextOutput > should handle empty strings with ANSI codes 1`] = `
+"hello
+world"
+`;

packages/cli/src/ui/utils/textOutput.test.ts

@@ -0,0 +1,99 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/// <reference types="vitest/globals" />
+
+import type { MockInstance } from 'vitest';
+import { vi } from 'vitest';
+import { TextOutput } from './textOutput.js';
+
+describe('TextOutput', () => {
+  let stdoutSpy: MockInstance<typeof process.stdout.write>;
+  let textOutput: TextOutput;
+
+  beforeEach(() => {
+    stdoutSpy = vi
+      .spyOn(process.stdout, 'write')
+      .mockImplementation(() => true);
+    textOutput = new TextOutput();
+  });
+
+  afterEach(() => {
+    stdoutSpy.mockRestore();
+  });
+
+  const getWrittenOutput = () => stdoutSpy.mock.calls.map((c) => c[0]).join('');
+
+  it('write() should call process.stdout.write', () => {
+    textOutput.write('hello');
+    expect(stdoutSpy).toHaveBeenCalledWith('hello');
+  });
+
+  it('write() should not call process.stdout.write for empty strings', () => {
+    textOutput.write('');
+    expect(stdoutSpy).not.toHaveBeenCalled();
+  });
+
+  it('writeOnNewLine() should not add a newline if the last char was a newline', () => {
+    // Default state starts at the beginning of a line
+    textOutput.writeOnNewLine('hello');
+    expect(getWrittenOutput()).toBe('hello');
+  });
+
+  it('writeOnNewLine() should add a newline if the last char was not a newline', () => {
+    textOutput.write('previous');
+    textOutput.writeOnNewLine('hello');
+    expect(getWrittenOutput()).toBe('previous\nhello');
+  });
+
+  it('ensureTrailingNewline() should add a newline if one is missing', () => {
+    textOutput.write('hello');
+    textOutput.ensureTrailingNewline();
+    expect(getWrittenOutput()).toBe('hello\n');
+  });
+
+  it('ensureTrailingNewline() should not add a newline if one already exists', () => {
+    textOutput.write('hello\n');
+    textOutput.ensureTrailingNewline();
+    expect(getWrittenOutput()).toBe('hello\n');
+  });
+
+  it('should handle a sequence of calls correctly', () => {
+    textOutput.write('first');
+    textOutput.writeOnNewLine('second');
+    textOutput.write(' part');
+    textOutput.ensureTrailingNewline();
+    textOutput.ensureTrailingNewline(); // second call should do nothing
+    textOutput.write('third');
+
+    expect(getWrittenOutput()).toMatchSnapshot();
+  });
+
+  it('should correctly handle ANSI escape codes when determining line breaks', () => {
+    const blue = (s: string) => `\u001b[34m${s}\u001b[39m`;
+    const bold = (s: string) => `\u001b[1m${s}\u001b[22m`;
+
+    textOutput.write(blue('hello'));
+    textOutput.writeOnNewLine(bold('world'));
+    textOutput.write(blue('\n'));
+    textOutput.writeOnNewLine('next');
+
+    expect(getWrittenOutput()).toMatchSnapshot();
+  });
+
+  it('should handle empty strings with ANSI codes', () => {
+    textOutput.write('hello');
+    textOutput.write('\u001b[34m\u001b[39m'); // Empty blue string
+    textOutput.writeOnNewLine('world');
+    expect(getWrittenOutput()).toMatchSnapshot();
+  });
+
+  it('should handle ANSI codes that do not end with a newline', () => {
+    textOutput.write('hello\u001b[34m');
+    textOutput.writeOnNewLine('world');
+    expect(getWrittenOutput()).toMatchSnapshot();
+  });
+});

packages/cli/src/ui/utils/textOutput.ts

@@ -0,0 +1,54 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * A utility to manage writing text to stdout, ensuring that newlines
+ * are handled consistently and robustly across the application.
+ */
+
+import stripAnsi from 'strip-ansi';
+
+export class TextOutput {
+  private atStartOfLine = true;
+
+  /**
+   * Writes a string to stdout.
+   * @param str The string to write.
+   */
+  write(str: string): void {
+    if (str.length === 0) {
+      return;
+    }
+    process.stdout.write(str);
+    const strippedStr = stripAnsi(str);
+    if (strippedStr.length > 0) {
+      this.atStartOfLine = strippedStr.endsWith('\n');
+    }
+  }
+
+  /**
+   * Writes a string to stdout, ensuring it starts on a new line.
+   * If the previous output did not end with a newline, one will be added.
+   * This prevents adding extra blank lines if a newline already exists.
+   * @param str The string to write.
+   */
+  writeOnNewLine(str: string): void {
+    if (!this.atStartOfLine) {
+      this.write('\n');
+    }
+    this.write(str);
+  }
+
+  /**
+   * Ensures that the output ends with a newline. If the last character
+   * written was not a newline, one will be added.
+   */
+  ensureTrailingNewline(): void {
+    if (!this.atStartOfLine) {
+      this.write('\n');
+    }
+  }
+}