help: unknown_kind

What it means: host.tool_publish's kind argument named a kind this host doesn't register.

Likely cause: A typo ("pytho", "htpp"), or a word from another platform's vocabulary ("lambda", "function") that doesn't map onto this host's kinds.

Fix: Check data.registered and data.did_you_mean in the error payload; two real kinds exist today, python and http (echo is a stub, not a real tool).