Selecting text in a dialog input by click-dragging and releasing the mouse
outside the dialog closed it: the browser fires a `click` whose target is the
backdrop (mousedown was inside, mouseup outside), and the dismiss handler keyed
solely on `e.target === backdrop`.
Guard every backdrop click-to-close with a mousedown flag — close only when the
press ALSO started on the backdrop (a genuine backdrop click), not a drag that
began inside the dialog. Applied to the browse New file/folder party picker (the
reported case) and the other browse create dialogs (create/accept-transmittal,
stage), plus the classifier dialogs that share the pattern (copy chooser,
dir-picker, and the paste/match modal — whose textarea is a prime drag target).
The conflict/history dialogs already used mousedown and were unaffected.
Build + browse/classify/classifier suites green (80).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
