Development record

.abcd/development/brief/04-surfaces/21-update.md:26-30 names the launch preview and the release cut as the other commands reaching the release origin, and commands/update.md:18 calls --fetch-baseline the one other flag that does. `abcd session blueprint` and `abcd session setup` also read a release's checksums.txt from that origin (internal/surface/cli/session.go:70, 534, 798; .abcd/development/brief/04-surfaces/37-session.md:123).