Design 25 §7's second item. Two surfaces over one thing — a command line for somebody
at a terminal, an MCP server for an agent — and both are adapters over the same three
calls: what tools are there, what does this one take, call it. A second way of reaching
a tool would be a second thing to keep correct.
It uses the client a module's runtime uses. Not a bridge and not a second protocol: a
person connects as their own bus user and publishes on the tool subjects their account
permits, so "what may this person do" is answered by the same permission list that
answers it for a module, and an audit has nothing separate to read.
`mesh tools` lists what the *catalogue* has, not what this credential may call. The two
differ and the difference is the point: somebody seeing only their own tools cannot tell
"not installed" from "not yours", and those need different people to fix them.
A failed call says which of three things happened, because the remedies are in three
different places: nobody serves that tool, this credential may not call it, or the tool
itself was slow. Without that they are one timeout and a stack trace.
The MCP surface decides nothing. The tool names are the ones a person types, the schemas
are the modules' own, and an answer is passed through unshaped — an adapter that
summarised somebody else's answer would be deciding what matters in it. A tool that fails
comes back as a tool error rather than a protocol error, because the request was
well-formed and the mesh answered it.
Written against the protocol directly: it is three methods and one framing, and a
dependency here would be a dependency on every workstation.
Tests drive both surfaces against a real bus, including that a host's notification is
answered with nothing and an unknown method is refused. They run one file at a time,
because each stands up a module serving the same tool subjects and run together their
requests get split between them — which showed up as one test reading another's answer.
