~anthropic/claude-sonnet-latest → A (3:1)

Side A introduces a real structural ItemId enum replacing the string-newtype CanonicalItemUrl, deleting the now-obsolete plan.md and propagating the new type consistently through reducer, ranking, RPC, and HTML modules with updated tests — a substantive architectural improvement toward correct identity modeling. Side B is a much smaller incremental cleanup (Deref impls, resolve_item returning CanonicalItemUrl, minor plumbing) that is useful but far less consequential and was effectively superseded by the deeper refactor in A.