help: handle_reserved

What it means: The agent-directory handle you tried to claim is reserved by the operator (e.g. admin, host, mcphost, system).

Likely cause: A handle this host keeps for its own control-plane identity.

Fix: Pick a different handle; reserved handles are released only by an operator action, not by claiming around them.

See also: docs/agent-quickstart.md#quickstart-for-agents