The Coach loop's final round sent toolChoice "none" without the tool
definitions. With tool_use/tool_result blocks in the history Anthropic
refuses such a request (400), and OpenAI Chat Completions refuses
tool_choice without tools, so every budget, time, cap and no-progress stop
ended in an error on those wires. The final round now carries the tools
with toolChoice "none", which every wire accepts, thinking included.
Codex kept reasoning items as provider state even when the request asked
for no encrypted reasoning; replaying such an item under store:false is a
400. Items are kept only when the request included
reasoning.encrypted_content and the item carries it.
The reasoning dialect cache learned from any 4xx that mentioned
reasoning or thinking (auth, rate limits, model names such as
deepseek-reasoner) and from replay errors, and kept the downgrade for the
life of the process. Learning now requires an HTTP 400 that refuses a
sent parameter, ignores replay errors and the model name, and a learned
downgrade expires after an hour.
reasoningSupport() reads what each provider can do with reasoning from the provider type and model name: effort, summaries, live summaries, state that must travel between tool rounds, and whether off is a real off. Unknown names are treated optimistically.
The dialect cache records what an endpoint refused (keyed by provider, endpoint and model) so a client retries with the lesser request once and never pays the refused round-trip again. Downgrades are marked on the wide event with meta keys only.
Marc-André Bombeck