CoStrict DeepSeek-V4-Pro returns thinking content in `delta.reasoning`
(string) and `delta.reasoning_details` (array) instead of the standard
`delta.reasoning_content` field. Add extractReasoning() with priority
fallback so all three formats are mapped to Anthropic thinking blocks.
Co-Authored-By: Auto <noreply@anthropic.com>
DeepSeek v4 in thinking mode sometimes returns reasoning_content: ""
when the model answers directly without internal reasoning. Two places
were filtering the empty string out, which dropped the thinking block
from the assistant turn entirely. The next request then omitted
reasoning_content for that prior turn, and DeepSeek rejected with
400 "reasoning_content ... must be passed back to the API".
Fix:
- openaiStreamAdapter: open a thinking block whenever reasoning_content
is present (including ""); skip the empty thinking_delta event since
the empty value is already conveyed by the block's initial state.
- openaiConvertMessages: preserve empty thinking blocks as
reasoning_content: "" when serializing assistant messages back to
the OpenAI/DeepSeek format.
Tests:
- New: empty reasoning_content opens a thinking block (adapter).
- Updated: empty thinking blocks now round-trip as reasoning_content: ""
instead of being dropped.
- New: assistant messages with no thinking block still omit
reasoning_content (regression guard for non-thinking models).
