reloadSession checked streaming.value at entry but api.getSession is
async. While awaiting, onStreamStart could set streaming=true and push
the assistant message into messages.value. When reloadSession resumed it
replaced messages.value with the stale server snapshot, evicting the live
streaming message. All subsequent deltas and tool cards went to the orphan
and were invisible.

Fix: re-check streaming.value after the await before mutating messages.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>