ReActV2's last_request_note renders with an invented assistant reply

[deepfates]

What's true now. Imp.Predict.ReActV2's :last_request_note is documented as "one line of host text put in front of it as a user message" (lib/imp/predict/react_v2.ex ~115). It's stored as a history entry that has an input and no outputs (append_note/3), and the chat adapter renders every history entry as a complete exchange. So the note's entry becomes a user message followed by a made-up assistant message:

[[ ## next_thought ## ]]
Not supplied for this conversation history message.

[[ ## completed ## ]]

That's DSPy's filler for history entries missing an output (dspy/adapters/base.py:451, DSPy 3.2.1). It's right for DSPy's History, where every entry is a finished exchange. It's wrong for Imp's own note, which isn't an exchange. As a result, the last request of an interrupted turn ends on an invented assistant reply rather than on the note. Evidence: a Dwell capture with Dwell's output renderer removed (GroveResearch/dwell#148; scratchpad imp-renders/without-output-renderer/h-budget-request-4.txt).

Target. The note reaches the model as what the docs say it is: the last user message of that request, with no made-up assistant reply after it. The same holds anywhere ReActV2 stores an input-only entry of its own making. DSPy-shaped History inputs keep DSPy's behaviour.

Done when.

• A captured last request with a note ends on the note as a user message.
• The tests fail without the fix.
• The parity differentials are unchanged, or any change is recorded with its reason.
• It ships in 0.7.0: GroveResearch/dwell#148 carries a narrow renderer only until this lands.

[deepfates]

Correction to the issue body: "Not supplied for this conversation history message." is not DSPy's rendering of a history entry missing outputs. DSPy 3.2.1's ChatAdapter.format renders a missing history output as None (chat_adapter.py, format_assistant_message_content, outputs.get(k, missing_field_message) with no message given; checked by running it in the pinned venv). "Not supplied ..." is DSPy's filler for demos (dspy/adapters/base.py:451). Imp uses it for history entries too (lib/imp/adapter/chat.ex, render_history_turns/3), which is an older Imp divergence from DSPy. #260 fixes the note without changing that divergence.