openai/gpt-chat-latest → A (4:1)

Side A introduces a substantial URL identity architecture: a new composable `url_rules` module, canonical full-URL `ItemId`s, centralized canonicalization/parent/breadcrumb logic, replay support, and updates projection, Reddit integration, and storage parsing to use the new canonical identities. Side B is primarily a refactor separating identity and path normalization plus changing wire formats (removing `@` from stored/API identities and making delegates optional), which improves organization and API consistency but is less foundational than the new canonical URL system and normalization behavior added in Side A.