Before: textInput explicitly ignored Ctrl+C so the app-level handler took
over — with no knowledge of the TextInput's own selection — and fell through
to clearIn() whenever input had text. Selecting part of the composer and
pressing Ctrl+C silently nuked everything you typed.
Now: Ctrl+C with an active in-input selection writes the selected substring
to the clipboard via OSC 52 and clears the selection. The original semantics
(Ctrl+C with no selection → app-level interrupt/clear/die chain) are
preserved by still returning early in that case.
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