Constant CAMEL_STOP 

pub const CAMEL_STOP: &str = "CamelStop";

Pipeline-executor-recognized stop signal. Set by processors (ThrottleStrategy::Drop, SamplingService) that cannot return PipelineOutcome::Stopped directly because they are Tower Service (Process mode), not OutcomePipeline (Segment). The executor checks this after each step completion. See ADR-0024 amendment.