On terminals that send a bare LF for plain Enter (WSL is the case
prompt_toolkit itself calls out), Alt+Enter arrives as ESC + LF
("\x1b\x0a" = Escape + ControlJ), not the ESC + CR the existing
"escape","enter" binding matches. The Escape was swallowed and the bare
LF hit prompt_toolkit's default submit, so the documented "universally
supported" Alt+Enter newline fallback failed on exactly the terminal path
plain Enter is preserved for.
Bind ESC + ControlJ to insert a newline too, and add a real-PromptSession
regression test covering the WSL Alt+Enter path.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
77a6003255