Constant BACKPRESSURE_DOMAIN 

pub const BACKPRESSURE_DOMAIN: &str = "ai.bytesandbrains.backpressure";

Domain string the framework uses to namespace the backpressure protocol per bb-runtime/src/bus.rs:155 reserved framework prefix. Surfaced for cross-referencing in docs + tests; the actual routing key is the per-fill type_hash from backoff_notice_type_hash.