feat(groq): native content-block streaming events

[Nick Hollon (nick-hollon-lc)]

Stacked on #37995 (core BlockStreamTracker + Anthropic), which it branches from. Depends only on the core primitive — sibling of the OpenAI chain. Retargets to master once #37995 lands.

Gives ChatGroq native _stream_chat_model_events / _astream_chat_model_events hooks so stream_events(version="v3") maps groq's stream directly to content-block events.

How it works

A bespoke converter (convert_groq_stream / async twin) builds text, reasoning, and tool-call blocks directly from groq's raw OpenAI-shaped delta, feeding the shared BlockStreamTracker. groq streams tool-call arguments incrementally (id+name on the first delta, fragments on later deltas at the same index), so the tracker accumulates them and finalizes to a parsed dict. Usage is read from x_groq.usage; the arguments == "null" quirk is normalized to "{}".

It deliberately does not depend on langchain-openai — it reuses only groq's own _create_usage_metadata.

The win over the bridge

groq's existing chunk parser puts tool_calls and reasoning in additional_kwargs, so the compat bridge surfaces neither as content blocks. The native converter surfaces both — tool calls as tool_call blocks and reasoning as reasoning blocks.

Worth careful review

• Tool-arg accumulation across deltas (keyed by tool:{index}); a test covers parallel tool calls at distinct indices.
• message_id is keyword-only on the hooks, kept out of the request kwargs; message-start carries core's LangChain run id.
• Scope cut: groq server-tool results (executed_tools) are not yet surfaced as blocks (noted in-code); the bridge still carried them in additional_kwargs.
• Sync/async are faithful twins.

[open-swe]

Open SWE Review found 1 potential issue.

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[open-swe]

🟡 Logprobs dropped from v3 streams

The native converter only carries finish_reason into the final message-finish.metadata. Before this hook was added, Groq v3 events used the compat bridge over _stream(), and _stream() preserves choice["logprobs"] in generation_info, which chunks_to_events() forwards into the final metadata. With the new path, ChatGroq(...).stream_events(..., version="v3", logprobs=True) silently loses the returned logprobs even though they are present on the raw choice. The async twin has the same issue at lines 144-145, so both converters should copy choice.get("logprobs") into response_metadata like _stream() does.

(Refers to lines 109-110)

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