Empty tool chunk IDs now treated as missing in merge operations

langchain-core 1.2.16 changes how empty tool chunk IDs are handled during merge — treating them as missing rather than valid identifiers. This prevents merge conflicts when streaming tool calls without explicit IDs.

Test streaming tool call implementations after upgrading to 1.2.16. Verify that tools without explicit chunk IDs merge correctly. Monitor langchain_tool_error for merge-related failures in streaming contexts.