repl: Garbled string on paste into non-last position

[silverwind]

Version

v24.10.0, v25.0.0

Platform

Darwin, Linux

Subsystem

repl

What steps will reproduce the bug?

1. Open REPL
2. Enter {} into the prompt
3. Move cursor one position to the left, between the brackets
4. Paste text "Node"

What is the expected behavior? Why is that the expected behavior?

The prompt to read {Node}.

What do you see instead?

The prompt reads {}Noed.

Additional Information

Works fine on v24.7.0. I suspect this is a regression from #59857.