fix(cli): support WSL2 clipboard image paste

[Pluviobyte]

Summary

• Detect WSL environments before the native Linux clipboard tool path.
• Use PowerShell interop from WSL to read the Windows clipboard and save images as PNG files.
• Share the PowerShell image save helper with the native Windows path and cover WSL behavior with tests.

Fixes #22274

Test plan

• npx vitest run src/ui/utils/clipboardUtils.test.ts src/ui/utils/clipboardUtils.windows.test.ts
• npx prettier --check packages/cli/src/ui/utils/clipboardUtils.ts packages/cli/src/ui/utils/clipboardUtils.test.ts packages/cli/src/ui/utils/clipboardUtils.windows.test.ts
• npx eslint packages/cli/src/ui/utils/clipboardUtils.ts packages/cli/src/ui/utils/clipboardUtils.test.ts packages/cli/src/ui/utils/clipboardUtils.windows.test.ts
• npm run typecheck --workspace @google/gemini-cli

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces support for pasting images from the clipboard when running in a WSL2 environment. By leveraging PowerShell interop, the CLI can now access the Windows clipboard from within Linux, ensuring a seamless experience for users working across the WSL boundary. The changes also refactor existing Windows clipboard logic into a shared utility to improve maintainability and consistency.

Highlights

• WSL2 Clipboard Support: Added detection for WSL environments to enable clipboard image access via PowerShell interop.
• PowerShell Interop: Implemented a shared helper function to read and save clipboard images using PowerShell, supporting both native Windows and WSL2.
• Test Coverage: Added comprehensive unit tests for WSL2 clipboard functionality, including path conversion and error handling.

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[gemini-code-assist]

Code Review

This pull request adds support for detecting and saving clipboard images in WSL2 environments by utilizing PowerShell interop and wslpath for path translation, alongside refactoring the Windows implementation to share a common helper. The review feedback highlights that checking PowerShell's stdout with strict equality after trimming is fragile due to potential extra output (like telemetry or BOM characters), and recommends using .includes() instead for more robust validation.

[gemini-code-assist]

Using stdout.trim() === 'True' is fragile because PowerShell can sometimes output extra text to stdout (such as update notifications, telemetry warnings, or BOM characters), even when -NoProfile is specified. If any extra text is printed, stdout.trim() will not equal 'True', causing the check to fail. Using stdout.includes('True') is much more robust and ensures the clipboard check works reliably across different user environments.

Suggested change

	return stdout.trim() === 'True';
	return stdout.includes('True');

[gemini-code-assist]

Using stdout.trim() !== 'success' is fragile because PowerShell can sometimes output extra text to stdout (such as update notifications, telemetry warnings, or BOM characters), even when -NoProfile is specified. If any extra text is printed, stdout.trim() will not equal 'success', causing the image save to fail. Using !stdout.includes('success') is much more robust and ensures the clipboard paste works reliably across different user environments.

Suggested change

	if (stdout.trim() !== 'success') {
	return false;
	}
	if (!stdout.includes('success')) {
	return false;
	}