Persisted assistant `reasoning_content` / `reasoning` fields are now emitted
as ACP `agent_thought_chunk` notifications during `_replay_session_history`,
so editor clients (Zed, etc.) rebuild collapsed Thinking panes when the user
re-opens a session that used a thinking model.
Ordering matches live streaming: thought precedes message text within the
same assistant turn, mirroring how `reasoning_callback` deltas arrive before
`stream_delta_callback` deltas in `events.py::make_thinking_cb` /
`make_message_cb`.
Behavior on non-reasoning histories is unchanged; the replay loop's existing
text / tool_call / tool_call_update / plan emission is preserved bit-for-bit.
Closes#12285.
Credit:
- @Yukipukii1 (#14691) — original thought-replay design via
`acp.update_agent_thought_text`; the tool-call portion of that PR has
since landed via #19139, but the reasoning replay is theirs.
- @HenkDz (#17652 / #18578) — established the `_replay_session_history` and
`_history_*` helper conventions this builds on.
- @D1zzyDwarf (#16531) — also closed by this work.
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