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Context

An MCP server bolted on beside an app drifts from it: it checks permissions its own way, validates less, and falls behind on features.

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Decision

All logic lives in src/lib/core/. The REST routes, the MCP server (POST /api/v1/mcp) and the CLI are thin adapters over it: they parse, call core, and shape the answer. MCP is hand-rolled, stateless JSON-RPC over Streamable HTTP, not the SDK: tools and resources are all it serves.

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Consequences

  • A permission is checked once, in core, for every door.
  • An MCP tool is usually a few lines over an existing core function.
  • Prompts, subscriptions or server-initiated messages would need the SDK; that is the trigger to take it.