"\x1b[27;2;13~" (the older xterm modifyOtherKeys / rxvt encoding of
Shift+Enter) is already registered by prompt_toolkit by default -- as
Keys.ControlM, i.e. plain Enter/submit. The previous `setdefault()` call was
therefore a silent no-op against it: this Shift+Enter variant kept behaving
like a submit instead of inserting a newline, even after the ControlJ/WSL
fix, since setdefault only sets missing keys.
Assign directly to override that default for both known Shift+Enter
sequences, since inserting a newline is the whole point of the binding.
Add a regression test driving a real PromptSession/parser with this exact
sequence, since a mocked-buffer test can't observe prompt_toolkit's default
ANSI_SEQUENCES entries taking priority.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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