CI caught a split defect in this salvage: the PR's long-reasoning tail
test was kept but its production hunk was dropped as 'cosmetics'. It
isn't — cleanThinkingText runs several full-string regex passes and
reasoning grows on every streamed token, so re-cleaning the whole
accumulated string per chunk is O(n) per token / O(n^2) per stream.
Only the tail is displayed (boundedLiveRenderText caps it downstream),
so bound the input to 1.5x LIVE_RENDER_MAX_CHARS first.
Restores the one text.ts hunk from cd99e65fc (author preserved); the
italic-thinking display change and profile script from that commit
remain out of scope.
64882bc684