Function setup_cached_mcp 

pub async fn setup_cached_mcp(
    registry: &Arc<RwLock<ToolRegistry>>,
) -> (usize, Option<PendingMcpDiscovery>)

Background-mode phase 1 (McpDiscovery::Background): register the cached descriptors only — never spawns — and hand back the discovery still owed for servers without a fingerprint-matching entry (None when there is none). Returns (tools registered, pending discovery).