fix: Ensure filename is available for diff rendering in write-file

This commit resolves a bug where the `write-file` operation could fail to render content due to a missing filename.

The fix involves:
- Ensuring `fileName` is consistently passed to `DiffRenderer.tsx` through `ToolConfirmationMessage.tsx`, `ToolMessage.tsx`, and `useGeminiStream.ts`.
- Modifying `edit.ts` and `write-file.ts` to include `fileName` in the `FileDiff` object.
- Expanding the `FileDiff` interface in `tools.ts` to include `fileName`.

Additionally, this commit enhances the diff rendering by:
- Adding syntax highlighting based on file extension in `DiffRenderer.tsx`.
- Adding more language mappings to `getLanguageFromExtension` in `DiffRenderer.tsx`.
- Added lots of tests for all the above.

Fixes https://b.corp.google.com/issues/418125982

packages/cli/src/ui/components/messages/DiffRenderer.test.tsx

@@ -0,0 +1,117 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { render } from 'ink-testing-library';
+import { DiffRenderer } from './DiffRenderer.js';
+import * as CodeColorizer from '../../utils/CodeColorizer.js';
+import { vi } from 'vitest';
+
+describe('<DiffRenderer />', () => {
+  const mockColorizeCode = vi.spyOn(CodeColorizer, 'colorizeCode');
+
+  beforeEach(() => {
+    mockColorizeCode.mockClear();
+  });
+
+  it('should call colorizeCode with correct language for new file with known extension', () => {
+    const newFileDiffContent = `
+diff --git a/test.py b/test.py
+new file mode 100644
+index 0000000..e69de29
+--- /dev/null
++++ b/test.py
+@@ -0,0 +1 @@
++print("hello world")
+`;
+    render(
+      <DiffRenderer diffContent={newFileDiffContent} filename="test.py" />,
+    );
+    expect(mockColorizeCode).toHaveBeenCalledWith(
+      'print("hello world")',
+      'python',
+    );
+  });
+
+  it('should call colorizeCode with null language for new file with unknown extension', () => {
+    const newFileDiffContent = `
+diff --git a/test.unknown b/test.unknown
+new file mode 100644
+index 0000000..e69de29
+--- /dev/null
++++ b/test.unknown
+@@ -0,0 +1 @@
++some content
+`;
+    render(
+      <DiffRenderer diffContent={newFileDiffContent} filename="test.unknown" />,
+    );
+    expect(mockColorizeCode).toHaveBeenCalledWith('some content', null);
+  });
+
+  it('should call colorizeCode with null language for new file if no filename is provided', () => {
+    const newFileDiffContent = `
+diff --git a/test.txt b/test.txt
+new file mode 100644
+index 0000000..e69de29
+--- /dev/null
++++ b/test.txt
+@@ -0,0 +1 @@
++some text content
+`;
+    render(<DiffRenderer diffContent={newFileDiffContent} />);
+    expect(mockColorizeCode).toHaveBeenCalledWith('some text content', null);
+  });
+
+  it('should render diff content for existing file (not calling colorizeCode directly for the whole block)', () => {
+    const existingFileDiffContent = `
+diff --git a/test.txt b/test.txt
+index 0000001..0000002 100644
+--- a/test.txt
++++ b/test.txt
+@@ -1 +1 @@
+-old line
++new line
+`;
+    const { lastFrame } = render(
+      <DiffRenderer
+        diffContent={existingFileDiffContent}
+        filename="test.txt"
+      />,
+    );
+    // colorizeCode is used internally by the line-by-line rendering, not for the whole block
+    expect(mockColorizeCode).not.toHaveBeenCalledWith(
+      expect.stringContaining('old line'),
+      expect.anything(),
+    );
+    expect(mockColorizeCode).not.toHaveBeenCalledWith(
+      expect.stringContaining('new line'),
+      expect.anything(),
+    );
+    const output = lastFrame();
+    const lines = output!.split('\n');
+    expect(lines[0]).toBe('1 - old line');
+    expect(lines[1]).toBe('1 + new line');
+  });
+
+  it('should handle diff with only header and no changes', () => {
+    const noChangeDiff = `diff --git a/file.txt b/file.txt
+index 1234567..1234567 100644
+--- a/file.txt
++++ b/file.txt
+`;
+    const { lastFrame } = render(
+      <DiffRenderer diffContent={noChangeDiff} filename="file.txt" />,
+    );
+    expect(lastFrame()).toContain('No changes detected');
+    expect(mockColorizeCode).not.toHaveBeenCalled();
+  });
+
+  it('should handle empty diff content', () => {
+    const { lastFrame } = render(<DiffRenderer diffContent="" />);
+    expect(lastFrame()).toContain('No diff content');
+    expect(mockColorizeCode).not.toHaveBeenCalled();
+  });
+});