* fix(agent): strip stale reasoning_content when falling back to a strict provider
A reasoning primary (DeepSeek/Kimi/MiMo thinking mode) pins reasoning_content
on every assistant tool-call turn (a single space " " pad). api_messages is
built once under the primary; on a mid-session fallback to a strict
OpenAI-compatible provider (Mistral, Cerebras, Groq, SambaNova), those stale
pads were replayed verbatim and rejected with HTTP 400/422:
body.messages.2.assistant.reasoning_content: Extra inputs are not
permitted (input: ' ')
reapply_reasoning_echo_for_provider() only ever ADDED pads, so it never
reconciled history built under a reasoning primary against a strict fallback.
copy_reasoning_content_for_api() also leaked empty-string and 'reasoning'-only
shapes to non-pad providers.
Fix both sites: when the active provider does not enforce echo-back, strip
reasoning_content (empty, space-pad, or non-empty) entirely. Re-padding when
switching TO a reasoning provider is preserved. Covers the Cerebras 400 from
#45655 and the DeepSeek->Mistral 422 fallback report.
Refs #45655.
* test: update reasoning-replay tests for strict-provider stripping
test_explicit_reasoning_content_beats_normalized_reasoning_on_replay was
implicitly running on the OpenRouter fixture (non-pad); pin it to a reasoning
provider so the precedence it checks is observable. Add a positive
strict-provider test asserting reasoning_content is stripped on replay.
Teknium
2b3a4f0af8