Support file-manager drops in macOS webviews

[dominicletz]

Summary

• Add FileDropWebView for Finder file URLs and file promises.
• Preserve WebKit drag handling so pages receive drop and dataTransfer.files.
• Use the custom webview after window.open and webview.rebuild.
• Make file-manager drag-and-drop a required feature for macOS, Windows, and Linux.
• Document the platform hooks and manual checks.

Checks

• ./scripts/build_macos.sh
• MIX_ENV=test NO_WX=1 mix test.unit
• MIX_ENV=test NO_WX=1 mix test.e2e
• mix format --check-formatted

All automated checks pass. Native picker and Finder, Explorer, and Linux file-manager drag checks need an interactive desktop.

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Note

Low Risk
macOS-only native change is limited to drag registration and forwarding around WKWebView; protocol/docs updates are additive with no auth or RPC behavior changes.

Overview
Adds Finder file-manager drag-and-drop on macOS by introducing FileDropWebView, a WKWebView subclass that registers file URL and file-promise pasteboard types, accepts Finder drags when WebKit would not, and delegates drop handling to WebKit so pages get normal drop events with dataTransfer.files. WebWindow now creates FileDropWebView on initial window setup and on webview.rebuild.

Documentation treats file-manager drag-and-drop as a required host feature on macOS, Windows, and Linux (alongside HTML file inputs), with a new normative section in docs/protocol.md, updated porting hooks, status matrix rows, and platform READMEs. Windows/Linux behavior is specified as preserving engine drag handling—no native code changes in this PR beyond macOS.

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Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

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Rejected file drops are force-accepted

Medium Severity

FileDropWebView returns .copy and prepares the drop when the pasteboard has file types and WebKit reports no operation. performDragOperation then only forwards to WebKit. That accepts drops the page already refused, so WebKit may load the file:// URL instead of firing a page drop with dataTransfer.files. File-promise drags can also show a copy cursor and still deliver an empty FileList.

Additional Locations (1)

• native/macos/Sources/DesktopWebView/FileDropWebView.swift#L43-L46

 

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