Function build_host 

pub fn build_host(
    config: Config,
    providers: ProviderRegistry,
    runs_dir: PathBuf,
    shared_mcp: Arc<Mutex<ToolExecutor>>,
    mcp_tool_defs: Vec<Tool>,
    mcp_pool: Arc<McpPool>,
    runtime: Handle,
    now_secs: fn() -> i64,
) -> WorldHost

Build the daemon’s WorldHost: one world hosting every agent, its tool service + interaction hub, and a Spawn-op spawner that loads blueprints and registers per-agent tool state. shared_mcp / mcp_tool_defs are the MCP connections built once at startup and reused by every agent.