StateViewCache

The shared cache of another context's aggregate states, each read as its generated view V (the <State>View of the context's api module): what a Saga, a name lookup or an internal computation reads instead of querying the context on every call.

• Kept by the context that owns the aggregate. The owner writes each state into the cache after its own commit, in version order, so the cache follows the aggregate; a deleted aggregate reads as null. A state the cache does not hold is read from the owner (its typed query, in process or over HTTP as this service) and cached, an absent one too, for a while.

• Declared by no one. A service injects StateViewCache<OrderStateView>: everything else (the cache's name, its keys, the view's JSON) follows from the view, on the owner and on every reader alike.

• When it cannot serve. A state the cache does not hold, whose owner cannot be read now, is a StateViewUnavailableException. A read for the reader's own use (a name, a description) may fall back on it; a read a decision rests on must not, and fails as the owner's read fails. The cache logs the first such failure at WARN, and the next ones at DEBUG until it serves a read again, so a reader that falls back logs nothing itself.

• A trusted read. The cache holds the full view as this service's identity sees it, for every tenant and owner: never return it to an end user as it is, nor decide by it what the owner alone decides. A command's decision rests on its own aggregate's state; a check that must be consistent is the owner's, which rejects the command.