Round two of review showed closing the dialog still left the canvas
open while the last page finished. The dialog now has no close button
and ignores Escape; Cancel reads "Cancelling…" and the dialog closes
once the capture has actually stopped, so the canvas takes no click or
drag while the app's coordinates are borrowed.

Keyboard shortcuts still reach the editor under the dialog. They change
stored world positions only (undo, switching pages), never convert from
the screen, and the capture works from the pages it loaded up front, so
they can't put content in the wrong place; the editor's drawing paths
are rebuilt after every capture, as before.

A cancel that lands during the last page now saves nothing: the capture
checks once more after its last page, and the toolbar before writing.
The page-content test compares pixels above the page names, so differing
captions can't pass it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>