Preview Pane (Monaco): Experimental Fix Attempt for Ctrl+C Copy Failure (#36474)

[VadiMIM11]

Summary of the Pull Request

This PR introduces an experimental fix attempt for clipboard copy (Ctrl + C) not working in Monaco-based File Explorer Preview (Issue #36474).
Our team investigated the interaction between Monaco Editor, WebView2, and the WinForms hosting layer used in PowerToys Preview Handlers. We identified that clipboard hotkeys were not propagated correctly from WebView2 to Monaco, resulting in Office reporting: "Clipboard item not collected: Format not supported by Office Clipboard."

As a mitigation attempt, we added a WebView2 KeyDown handler that explicitly forwards Ctrl+C to Monaco via a JavaScript runCopyCommand() call.

Although the fix passed existing tests, it caused Monaco-based previews to stop working on our local development environment. Even after restoring to a clean installation of PowerToys, Monaco previews remained unresponsive.
Because of that, this PR is not a final fix, but instead contributes investigation results, hypotheses, and a minimal reproducible implementation that future contributors can build on.

We hope that this work will accelerate root-cause diagnosis by maintainers familiar with the Monaco/WebView2 integration layer.

---

PR Checklist

• Closes: copy using CTRL-C from file preview (monaco) : format not supported by Office Clipboard #36474
• Communication: Shared approach and findings in the issue discussion.
• Tests: Existing tests pass; no new tests added due to non-final nature of the fix.
• Localization: No user-facing strings changed.
• Dev docs: Not updated (pending final resolution)
• New binaries: Not applicable
• Documentation updated: N/A

---

Detailed Description of the Pull Request / Additional comments

Root Cause Investigation

Based on our testing and review of the following PowerToys documentation:

• FilePreviewCommon.md architecture (Preview Handler pipeline)
• Monaco Editor integration through WebView2 (monaco-editor.md)

We believe the problem occurs in the boundary between WinForms → WebView2 → Monaco Editor.

Our primary hypotheses:

1. Monaco Editor loses input focus inside WebView2, resulting in Monaco not receiving Ctrl + C at all.
2. Key event suppression (e.Handled = true) in WinForms or WebView2 may prevent normal copy event propagation.
3. Monaco does execute the copy command, but the resulting clipboard data is written in an unsupported or corrupted format, which aligns with the Office Clipboard error reported in copy using CTRL-C from file preview (monaco) : format not supported by Office Clipboard #36474.

Code Changes Introduced

To test hypothesis #1 and #2, we added a fallback override that captures Ctrl + C at the WebView2 layer and explicitly executes Monaco’s internal copy command via injected JavaScript:

_webView.KeyDown += WebView2_KeyDown;
_webView.BringToFront();

private async void WebView2_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
    // Check for Ctrl+C
    if (e.Control && e.KeyCode == Keys.C)
    {
        if (_webView.CoreWebView2 != null)
        {
            await _webView.CoreWebView2.ExecuteScriptAsync("runCopyCommand()");
        }

        e.Handled = true;
    }
}

---

Results

• All existing tests passed.
• However, Monaco-based previews stopped functioning on our development machine after applying this code.
• Full cleanup (removing build outputs, reinstalling stable PowerToys) did not restore preview functionality, suggesting the attempted fix may have triggered a deeper side effect in Monaco or WebView2 integration into File Explorer.

Because of these unintended consequences, this PR is not intended to be merged as-is but as a contribution of debugging context and a minimal code example for further investigation by maintainers.

---

Validation Steps Performed

1. Manual testing across several text and source-code file types.
2. Verified that existing automated tests still pass.
3. Observed preview handler failure after applying patch, even after environment cleanup.

---

Additional Notes

We encourage deeper investigation from contributors familiar with:

• PowerToys ↔ WebView2 lifetime and focus management
• Monaco integration patterns (especially clipboard fallback hooks)
• Clipboard format negotiation when interacting with Office Clipboard

We hope this contribution accelerates root cause analysis for #36474.

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