handle_enter dispatches /steer and /model inline on the UI thread while
the agent is running, calling buffer.reset() then returning. Unlike every
other early-return branch in the handler, these two skipped
event.app.invalidate(). process_command() prints through patch_stdout
(scrolls output above the prompt without redrawing the input line), so the
just-cleared input area could keep showing the submitted '/steer <text>'
until an unrelated redraw fired — looking unsent and inviting an accidental
re-submit.
Add event.app.invalidate() after reset in both inline branches to match
the sibling branches. AST regression test pins the invariant: every
reset-then-return branch in handle_enter must invalidate first.
Fixes#34569
04de307d62