Live turn rendering used to show the streaming assistant text as one
blob with tool calls pooled in a separate section below, so the live
view drifted from the reload view (which threads tool rows inline via
toTranscriptMessages). Model now mirrors reload:
- turnStore gains streamSegments (completed assistant chunks, each
with any tool rows that landed between its predecessor and itself)
and streamPendingTools (tool rows waiting for the next chunk)
- turnController.flushStreamingSegment() seals the current bufRef into
a segment when a new tool.start fires; pending tools get attached to
that next chunk so order matches reload hydration
- recordMessageComplete returns finalMessages instead of one payload,
so appendMessage gets the same shape for live-ending turns as for
reloaded ones
- appLayout renders segments before the progress/streaming area, and
the streaming message + pending-tools fallback carry whatever tools
arrived after the last assistant chunk