[sdottaka]

Summary

• Defer canvas resizing until the pasted image is committed.
• Resize the canvas and paste the image as a single undoable operation.
• Commit overlapped images before switching pages or copying differences.
• Update scrollbars when cancelling a paste preview or switching pages.
• Clip deletion rectangles to the image bounds to prevent out-of-range access.

[Copilot]

🟡 Changes recommended

Cancellation can cause out-of-bounds writes, discard independent edits, and leave stale scrollbar state.

3 open issues

• Stale paste snapshot survives edits and page switches · New
• Delete uses stale rectangle after oversized paste cancellation · New
• Scrollbars remain stale after restoring canvas dimensions · New

What changed in this PR

Preserves the pre-paste image so undo can restore its original dimensions and content.

Changes:

• Saves the original image before paste resizing and reuses it for undo.
• Restores pending paste snapshots on cancellation and clears them on close.

File	Description
src/​WinIMergeLib/​ImgMergeWindow.hpp	Uses paste-specific resizing and cancellation.
src/​WinIMergeLib/​ImgMergeBuffer.hpp	Manages original-image snapshots for paste undo and cancellation.

_{Review effort: Balanced}