Revisits #13729. That PR buffered each `tool.complete`'s inline_diff
and merged them into the final assistant message body as a fenced
```diff block. The merge-at-end placement reads as "the agent wrote
this after the summary", even when the edit fired mid-turn — which
is both misleading and (per blitz feedback) feels like noise tacked
onto the end of every task.
Segment-anchored placement instead:
- On tool.complete with inline_diff, `pushInlineDiffSegment` calls
`flushStreamingSegment` first (so any in-progress narration lands
as its own segment), then pushes the ```diff block as its own
segment into segmentMessages. The diff is now anchored BETWEEN the
narration that preceded the edit and whatever the agent streams
afterwards, which is where the edit actually happened.
- `recordMessageComplete` no longer merges buffered diffs. The only
remaining dedupe is "drop diff-only segments whose body the final
assistant text narrates verbatim (or whose diff fence the final
text already contains)" — same tradeoff as before, kept so an
agent that narrates its own diff doesn't render two stacked copies.
- Drops `pendingInlineDiffs` and `queueInlineDiff` — buffer + end-
merge machinery is gone; segmentMessages is now the only source
of truth.
Side benefit: Ctrl+C interrupt (`interruptTurn`) iterates
segmentMessages, so diff segments are now preserved in the
transcript when the user cancels after an edit. Previously the
pending buffer was silently dropped on interrupt.
Reported by Teknium during blitz usage: "no diffs are ever at the
end because it didn't make this file edit after the final message".
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