Development record

The v0.15.1 release review found the brief at .abcd/development/brief/04-surfaces/37-reserve.md:84-93 out of step with the shipped code. It says: Each reservation commit's trailers name the record (Abcd-Reservation), holder, copy, footprint, lease (Abcd-Claimed-At, Abcd-Expires-At) and the Assisted-by label; a release adds Abcd-Released-At; a hand-back adds Abcd-Handed-Back and Abcd… In the code: A drain lane's renewal of the reservation also writes an Abcd-Stage trailer (internal/core/claim/stage.go keyStage, one of worktree|brief|implement|validate|land, validated by validateStage on read). The reserve chapter never names it; its only documented home is .abcd/development/brief/04-surfaces/08-abcd.md:241-242.