At the step limit, one request with no tools, and the prose is the answer

[deepfates]

Imp.Predict.ReActV2 ended a turn that reached max_iters with forced_submit: one more request with tool_choice naming the submit tool. For a host whose signature has a single text output and whose model already ends turns by writing prose, that asks the model to call a tool it never chose.

on_max_iters says what the step limit does.

• :forced_submit, the default, is today's behaviour, so existing users are unchanged.
• :last_prose makes exactly one more request with no tools in it: :tools and :tool_choice are dropped from the provider config, and for the chat completions profile a body with no tool roster carries neither key. The completion is parsed as prose the way the :answered path is, and the run finishes with the single text output set to that prose and termination_reason: :last_prose. An empty completion finishes with an empty answer rather than an error. The option needs a signature with exactly one output of type :string; anything else is refused at construction.

:last_prose is a separate reason from :answered: :answered is the model choosing to stop calling tools, :last_prose is the loop taking the tools away.

last_prose_note, nil or a string, puts one line of host text in front of that request as a user message. It goes through the same history mechanism forced_submit_notice uses, so the record of the run carries it, but the two options stay separate and a host passes one or the other. Imp writes no sentence of its own.

The last request and its response are emitted as events like any step's, and the prose becomes a history turn the way an answered step's does.

Both options dump and load; a dump written before them loads as :forced_submit.

Tests: test/react_v2_last_prose_test.exs covers three requests at max_iters: 2 with no :tools key in the third, the note present and absent, an empty answer, the event record, the construction refusal for a two-output signature, the default still forcing a submit, and the dump/load round trip including an older dump. The existing forced-submit and prose tests are unchanged.

Gates: mix format, mix compile --warnings-as-errors, mix check (2865 tests, 0 failures), mix dialyzer.check (150 errors, 150 skipped, 0 unnecessary skips).