Constant MAX_ACP_CONTROL_ID_BYTES 

pub const MAX_ACP_CONTROL_ID_BYTES: usize = gate4agent_types::PROVIDER_EVENT_ID_MAX_BYTES; // 512usize

Mirrors gate4agent_types::PROVIDER_EVENT_ID_MAX_BYTES – the ACP control verbs’ mode_id/option_id/model_id and the agent stream’s tool_name/catalog id fields round-trip provider-minted ids through the same bound the provider event stream already validates them against.