Artifact: Proportionality Map — Three Decisions

Artifact-weight choice mapped to three decisions of varying reversibility -- exercises co-16.

Decision	Reversibility	Artifact chosen	Why
Rename an internal config flag, retry_max to carrier_retry_max	Trivially reversible; a single grep-and-replace	Inline PR comment	Low stakes, one file, no cross-team impact -- an RFC would spend review attention nobody needed to spend.
Add exponential backoff to the Carrier Adapter	Reversible, but touches production error-handling	PR description	One team, one component, moderate stakes -- co-09's structure gives a reviewer everything needed without a formal review cycle.
Adopt Kafka as the shipment event bus	Expensive to reverse; new infrastructure, new runbooks	Full RFC + ADR	High stakes, cross-team (SRE now owns on-call for it), genuinely hard to undo once other services depend on Kafka's replay.