Expand description
The external (MCP) dispatcher — the handler registry’s fallback.
Namespaced external names (mcp.<server>.<tool>) are discovered at
runtime, so they dispatch through one fallback handler instead of exact
registrations. Admission already happened (admit_external_tool against
the session’s derived grant surface); the loop brackets every call in
the external-effect log because admitted entries are durable; and the
result enters the conversation as an untrusted observation. Replay never
re-invokes the server: recorded outputs come back from the ledger.