Using local MCP over stdio as a seam for portable agentic applications

mostly_deterministic · reddit · 2026-08-29

The author proposes an architectural pattern called the "Agent Runtime Boundary" to address portability and determinacy in agentic systems. The approach splits the conversational harness from system invariants, using local MCP (via stdio) as the seam, combined with FastMCP, LangGraph, and LangChain. It distinguishes between ephemeral and long-running tools, enabling a spectrum from deterministic to fully agentic behavior while remaining portable across different harnesses with simple MCP configuration.

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