[BUG] `<a-s>` does not preserve the orginal main cursor selection

Version of Kakoune

v2026.05.21

Reproducer

Buffer:

This is a line
This is a line
This is a line
This is a line

Command: :exec '%<a-semicolon><a-s>'; echo %val{cursor_line}

Outcome

When using <a-s>, the main cursor moves to bottom of all the selections instead of remaining where it was

If my selection is [ ] and my main cursor is ->, pressing <a-s> moves the main cursor from:

-> [ This is a line
This is a line
This is a line
This is a line ]

to:

[ This is a line ]
[ This is a line ]
[ This is a line ]
-> [ This is a line ]

Expectations

For the main cursor to remain at the top line

Additional information

No response