A billing plan: an id, a monthly price (minor units / cents), a map of feature configurations and any recurring credit allowances it grants.

Feature configs:

• {:limit, n, :hard}: hard cap; blocks at n.
• {:metered, included, unit_price}: allow overage; bill beyond included.
• {:counter}: measured, never blocked, never billed; no denominator.
• {:feature, boolean}: plain feature access (no quota).
• {:feature, non_neg_integer}: a plan-level value with no counter behind it (seats, retention days, projects): always entitled; read it with AuroraMeter.feature_value/3.

recurring_credits is a list of allowance declarations in declaration order, each a map of name, amount, category, rollover and expires. It is empty unless the plan declares AuroraMeter.Plans.recurring_credits/2, which is what makes recurring grants off by default. AuroraMeter.Credits.Recurrences is the engine that reads it; a new declaration kind was added here rather than a new feature kind so every feature_config/0 consumer is untouched.

Identity

A plan is identified by {id, version}, not by id alone. version is a short opaque string the host chooses ("1" when a block declares none), effective_at is the UTC instant from which that version is the one a new subscription gets (nil means "from the beginning"), and fingerprint is the sha256 of the version's commercial content. Two deploys of the same {id, version} with different content raise AuroraMeter.PlanVersionConflictError rather than repricing every tenant: see Plans.