When a settled assistant turn carries _anchor_activity_scene and has mixed
content[] (text interleaved with tool_use), promote that ordering into anchor
scene rows (prose / tool / thinking rows in sequence) instead of only the raw
content[] fallback, and mirror the same scene model in the backend hydration
path so a cold reload reconstructs an identical transcript.
Also fixes: post-tool_use text/thinking in a NON-FINAL assistant message was
silently dropped — only the turn-final assistant's post-last-tool text is the
"final answer" tail; earlier assistant messages keep post-tool content as
activity rows. Tail thinking is excluded from the final-answer text but still
emitted as a thinking row (verified on both JS and Python paths).
Tool-row de-duplication is conservative — ID-equal always merges; name/
invocation matches are cardinality-gated and same-message; body-prefix is only
a secondary confirmation inside the id-flexible branch (also requires matching
started_at + compatible name + invocation). It biases toward an extra visible
tool card over ever silently merging two distinct calls.
Gate: Codex SAFE (tail-thinking edge verified already-handled both sides),
Opus SHIP (dedup fails toward duplicate-not-loss; non-final preservation, XSS,
non-mixed regression all clean), full suite 10778 passed (only the 4 known
pre-existing flakes). One non-blocking follow-up noted: bring the prose/thinking
peer-dedup into JS↔Python parity (cosmetic cold-reload extra-narration row).
Co-authored-by: franksong2702 <franksong2702@users.noreply.github.com>
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