mirror of
https://github.com/hwchase17/langchain.git
synced 2026-05-18 05:26:09 +00:00
f42d80ca1c
The v3 streaming path drops `additional_kwargs` from per-chunk `AIMessageChunk`s during assembly: `chunks_to_events` emits no event field for them, and `ChatModelStream._assemble_message` constructs the final `AIMessage` without an `additional_kwargs` argument. Non-streaming `ainvoke` returns the provider message unchanged, so streaming and non-streaming diverge for any provider that uses `additional_kwargs` to carry data outside the typed protocol blocks. ## How this surfaces The concrete failure mode is Gemini's `__gemini_function_call_thought_signatures__` — a per-tool-call signature blob the Google GenAI integration places in `additional_kwargs`, keyed by `tool_call_id`. Gemini requires that signature on follow-up turns to replay the prior thought trace; without it, multi-turn streaming flows lose thought continuity (and may regenerate thinking, charging additional reasoning tokens, or in some cases refuse). Other providers that use `additional_kwargs` (e.g. older `function_call` accumulators, custom routing metadata) hit the same gap; the fix is intentionally provider-agnostic. ## Fix Provider-agnostic, two seams: - `_compat_bridge` accumulates `msg.additional_kwargs` across chunks with `merge_dicts` (matching `AIMessageChunk`'s own merge semantics for fields that accumulate, like `function_call`) and emits the merged dict on the `message-finish` event as an off-spec extension. The bridge already uses one such extension (`metadata` on `MessageFinishData`); this PR follows the same pattern for `additional_kwargs`. - `ChatModelStream._finish` reads the new field; `_assemble_message` threads it onto the final `AIMessage` only when non-empty, preserving today's behavior of leaving `additional_kwargs` empty when no provider data needs to ride on it.