Design

Tracking: coilysiren/inbox#164 (concept), coilyco-bridge/deploy#40 (first consumer).

A umbra Guardfile, no handwritten code, becomes a Docker image that serves a working MCP and matching HTTP tool API. The .mcp.kdl is the whole contract: every can grant becomes one MCP tool and one POST /api/{tool-name} endpoint, with method, path template, and typed params authored inline. No per-server Go, no per-server Dockerfile, no per-server handler, and no per-tool input schema, because the engine derives it from the inline op definition.

Scope: the spec configures the image interior

The spec configures only which upstream API, how it authenticates, and which grants become which tools. mcp-beaver's job ends at a runnable image. Everything about exposing that image is out of scope: the Deployment, Service and port mapping, the ingress or tailnet route, and injecting a token as a mounted Secret. Those are templated by the generic chart mcp-beaver ships, which deploy consumes per-MCP and rolls out. The image stays unaware of how it is deployed: the spec never reaches down into a chart, and the chart treats the .mcp.kdl as opaque values it mounts and never parses.

Network HTTP, never stdio

These servers run always-on and are reached by URL. A remote pod cannot be driven over stdio, which co-locates server with client, so the interior always binds one HTTP listener. There is no transport fork to decide.

Built on umbra

mcp-beaver shares no code with ward, whose name it used to carry. The ward in wrap ward mcp <name> is umbra's inline grammar, not a dependency, and it moves when umbra moves. cli-mcp is read as a code reference only; transport and session plumbing is the official MCP Go SDK. umbra turns a Guardfile into a guarded surface in three layers: the upstream spec (here, the .mcp.kdl itself), the compiled policy IR, and the human KDL authoring layer, parsed and never evaluated. The engine carries zero upstream knowledge, so one engine drives every spec. umbra's own driver renders it into a CLI, and mcp-beaver renders the same operation set into MCP tools.