Closes issue #103 (found splitting a fix onto its own bookmark, 2026-10-11).
oxy bookmark show --json (and the hub's API) print heads as bare 64-digit hex, but oxy bookmark set NAME HASH… answered 'no change matches' until each was written #HASH. A 64-hex spec can only be a full hash (ChangeIds have 32 digits), so it now resolves as #HASH does, everywhere a change is named.
The issue's second half, documenting that bookmark create --only C leaves out changes C does not depend on, is left on issue #103.
Test: a_full_hash_resolves_without_its_hash_sign. Gate green (332 tests, clippy, fmt). Bookmark is main's heads plus this change.