Marker-presence snapshot stored under ORIGINAL_CONTENT_TYPE_INHERITED_EXTENSION.
Stored as Arc<OriginalContentTypeInherited> via Exchange::set_extension.
Pipeline-executor-recognized stop signal. Set by processors (ThrottleStrategy::Drop,
SamplingService) that cannot return PipelineOutcome::Stopped directly because they
are Tower Service<Exchange> (Process mode), not OutcomePipeline (Segment).
The executor checks this after each step completion. See ADR-0024 amendment.
Extension key for the Content-Type provenance snapshot taken with
ORIGINAL_MESSAGE_EXTENSION at route entry when use_original_message is
enabled. Capture replaces the snapshot unconditionally; restore reads it to
rebuild the inherited marker.