Observed

LangSmith integration is genuinely zero-code (two environment variables auto-instrument every LLM call, tool invocation, and graph step). The first-party MCP bridge is not seamless: langchain-mcp-adapters fails entirely when any single configured MCP server is down — no partial initialization, no skip-and-warn (#401, opened 2025-12-23, open and re-verified 2026-06-11) — and ProxyUser serialization breaks on LangGraph Cloud while working locally (#416, opened 2026-02-09, open).

1. UPDATE 2026-06-28: langchain-mcp-adapters 0.3.0 (2026-06-10) surfaces tool-execution errors as failed ToolMessages but #401/#416 stay open; new failures: an MCP tool parameter named "config" is silently overwritten by RunnableConfig injection (#532) and the 0.3.0 upgrade raises ImportError on an mcp-SDK version gap (#550).