tool_search_tool_result parsing fails with streaming: empty tool call args despite valid partial_json

### Checked other resources - [x] This is a bug, not a usage question. - [x] I added a clear and descriptive title that summarizes this issue. - [x] I used the GitHub search to find a similar question and didn't find it. - [x] I am sure that this is a bug in LangChain rather than my code. - [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package). - [x] This is not related to the langchain-community package. - [x] I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS. ### Package (Required) - [ ] langchain - [ ] langchain-openai - [ ] langchain-anthropic - [ ] langchain-classic - [ ] langchain-core - [ ] langchain-cli - [ ] langchain-model-profiles - [ ] langchain-tests - [ ] langchain-text-splitters - [ ] langchain-chroma - [ ] langchain-deepseek - [ ] langchain-exa - [ ] langchain-fireworks - [ ] langchain-groq - [ ] langchain-huggingface - [ ] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-perplexity - [ ] langchain-prompty - [ ] langchain-qdrant - [ ] langchain-xai - [ ] Other / not sure / general ### Reproduction Steps / Example Code (Python) ```python from langchain_anthropic import ChatAnthropic from anthropic.types.beta import BetaToolSearchToolRegex20251119Param from langchain_core.messages import HumanMessage from langchain.tools import tool # Initialize Claude with tool search model = ChatAnthropic( model="claude-sonnet-4-5-20250929", betas=["advanced-tool-use-2025-11-20"], stream=True # Issue occurs with streaming ) # Define the tool search tool (must be non-deferred) tool_search = BetaToolSearchToolRegex20251119Param( name="tool_search_tool_regex", type="tool_search_tool_regex_20251119", ) # Define a deferred tool @tool(extras={"defer_loading": True}) def journal_search(search_term: str, page_size: int = 20, page_number: int = 0) -> str: """Search for academic journals. Args: …