Function resolve_agent_for_s1 

fn resolve_agent_for_s1(
    state: &AppState,
    agent_id: &str,
) -> Result<AgentDefinition, String>

Resolve the agent definition behind an S1-authenticated agent_id.

check_s1 authenticates a SLUG, not a UUID. RpcContext.agent_id is “slug of the authenticated agent from bus:register” (its doc in rpc_types/misc.rs), while agent_def_get queries db_agents by its UUID primary key — so calling it with the authenticated value returns None for every real caller (#3156).

Delegates to resolve_agent_definition_id, the existing resolver for exactly this, rather than hand-rolling the lookup: it already carries the registry-only fallback a previous review round forced in, for a live agent that never created a local db_agents row. A fresh two-tier lookup here would have that hole again.