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Add `BaseChatModel.stream_v2()` / `astream_v2()` returning a `ChatModelStream` with typed projections (`.text`, `.reasoning`, `.tool_calls`, `.usage`, `.output`) plus raw protocol event iteration. Providers that only implement `_stream()` get a compat bridge that converts `AIMessageChunk`s to the content-block protocol lifecycle, preserving usage and response metadata for v1 parity. - New module `chat_model_stream.py` with `ChatModelStream`, `AsyncChatModelStream`, and push/pull projection hierarchy (`SyncProjection`, `SyncTextProjection`, `AsyncProjection`). - New module `_compat_bridge.py` that converts chunk streams to protocol events, with `response_metadata` preserved via `MessageStartData.metadata` and `MessageFinishData.metadata`. - `stream_v2` wires `on_chat_model_start` / `on_llm_end` / `on_llm_error` callbacks into the pump; `astream_v2` spawns a producer task and awaits it alongside the output so `on_llm_end` fires before `await stream` returns. - tool_use finish-reason inference runs after finalization so malformed tool-call JSON (finalized as `invalid_tool_call`) does not flip `finish_reason` to `"tool_use"`. - Add `langchain-protocol>=0.0.6` dependency (local path override retained for dev). Tests cover projection semantics, tool-call streaming (single + parallel + malformed args), async/sync event replay, callback firing, and v1 parity (text, tool calls, usage, response metadata, reasoning+text ordering, error propagation).