- Add 37 new tests covering the drag source side of the DND protocol
- Test drag offer registration/unregistration (t=o, t=O)
- Test drag MIME type offering with various operations (copy/move/both)
- Test pre-sent data for valid/invalid indices, chunked data, multiple MIMEs
- Test image thumbnails: valid RGBA/RGB, invalid formats, dimensions, chunking
- Test drag start failures (no window, no offer, image size mismatches)
- Test drag cancellation from client (t=E:y=-1)
- Test offer replacement, cleanup, and error propagation
- Test client_id propagation for drag operations
- Test resource cleanup on window close during drag build
- Fix double-free in drag_free_built_data: set ds.items=NULL after free
- Add drag_free_offer to destroy_fake_window_contents for proper cleanup
Agent-Logs-Url: https://github.com/kovidgoyal/kitty/sessions/f9868553-29a2-48c4-85c2-b6b8f686dccc
Co-authored-by: kovidgoyal <1308621+kovidgoyal@users.noreply.github.com>