T-228. Typing in the composer was lost whenever the input was torn down
and rebuilt — most visibly when a permission prompt takes the composer's
place (D-78), since the prompt card replaces the composer widget and its
TextEditingController went with it.
Hoist the draft out of the widget: ClaudeComposer gains initialValue +
onDraftChanged, and the pane holds a per-session draft map, seeding the
composer on (re)mount and clearing the entry on submit. Keying the
composer by session id means switching sessions in a pane swaps to that
session's own draft. Text and caret both survive.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
jpmschweitzerandClaude Opus 4.8
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