The previous comment claimed DeepSeek's API aliases v4-flash/v4-pro to
deepseek-reasoner, justifying the auto coercion via the legacy
reasoner's known 400 behavior. That had the alias direction inverted:
per DeepSeek's pricing page, deepseek-chat and deepseek-reasoner are
deprecated aliases for v4-flash's non-thinking and thinking modes
respectively, not the other way around.
The coercion itself is empirically correct, though. Live preflight
against deepseek-v4-flash with tool_choice=required produces a
deterministic HTTP 400 ("provider rejected forced tool selection") in
275ms. The behavior is consistent across the DeepSeek user community
- multiple downstream projects (pydantic-ai #5193, claude-code-router
#1378, opencode #24190, others) confirm V4 models reject forced tool
selection despite DeepSeek's chat-completion docs listing required as
a supported value. Server reality disagrees with documentation.
This commit updates only the comments in openai.go and openai_test.go
to point at the empirical evidence and the community confirmation.
The coercion behavior is unchanged.
rcourtman
9329258f8b