v0.2.1 - drift gate as pre-release verification Adds a tag-triggered drift gate to bairn's CI: each tag pipeline builds bairn, hits Famly's parent-side surface using the operator's own refreshing credentials, and diffs response shapes against the committed baseline at discovery/baselines/main/. The gate fails the tag pipeline (and blocks the binary from shipping) when drift is detected. Companion docs (NOTICE.md, discovery/PROTOCOL.md, ADR 0007) name the trigger model explicitly: tag push is a human action; this is not a recurring schedule against Famly's surface. No behaviour change in the binary itself beyond version reporting. Posture and conditions of use unchanged: NOTICE.md.