Summary

Support OpenAI-compatible Chat Completions stream chunks that emit thinking text under choices[0].delta.reasoning.

Fixes #

Type and Areas

Type:

bug fix

Areas:

AI adapters, Rust stream parsing, tests

Motivation / Impact

Some OpenAI-compatible providers stream reasoning text as delta.reasoning instead of delta.reasoning_content. This PR maps that alias into the unified reasoning_content path so downstream thinking accumulation and ThinkingChunk emission work consistently.

The added SSE fixture also covers a real-style leading assistant role chunk with empty content, confirming it is harmless while subsequent reasoning alias chunks are parsed.

Verification

• pnpm run fmt:rs
• cargo test -p bitfun-ai-adapters parses_reasoning_alias_chunk
• cargo test -p bitfun-ai-adapters openai_fixture_parses_reasoning_alias_into_thinking

Reviewer Notes

reasoning_content remains the first-priority field. The new reasoning alias is only used when reasoning_content is absent, before falling back to MiniMax reasoning_details.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.