The address table's vote on a chart retirement: StatifierPersistence.PinSource implemented over the address rows.

StatifierPersistence.Executions.retire_chart/4 counts the pins it can see itself and asks the host's pin sources for the ones it cannot. An address row is one it cannot: it lives in this package's table, in a package statifier_persistence does not depend on, and it is the reason a later event still reaches the execution it names (ADR-0002, section 1). A retirement taken while such a row stands would leave that event routed to an execution whose chart is gone.

What the count is

%{addresses: n}, where n is the number of address rows naming one of the executions in the context. The context's :execution_ids are the ids of the :active executions on the content hash, which the retire call has already read, and that is the only handle this source needs: an address row carries an execution_id and no content hash, so a source over this table can answer for a hash it cannot see. The content hash is therefore not read here.

No horizon is applied to the count. The horizon in StatifierRouter.Addresses.reap/2 runs from terminal_seen_at, which is stamped only once this package has seen the row's execution terminal, so a row naming an :active execution has no horizon running against it yet. The rows this source counts are live addresses by construction.

So the pin releases exactly when the address it stands for is gone: the execution finishes, the reaper stamps the row terminal and deletes it once the horizon has elapsed, and the next retire call counts one pin fewer. Nothing here retains a row, and nothing here deletes one.

How a host installs it

The behaviour's callback takes a content hash and a context and nothing else, so the configuration this source reads the table through has to be bound into the module. use StatifierRouter.PinSource writes that module, with :config an expression it evaluates on every call:

defmodule MyApp.RouterPins do
  use StatifierRouter.PinSource, config: MyApp.Router.config()
end

MyApp.Router.config/0 is the host's own: the same %StatifierRouter.Config{} it routes events with. The host then names the module at the retire call:

StatifierPersistence.Executions.retire_chart(store, content_hash, [MyApp.RouterPins])

A host that would rather not use a macro writes the same module by hand against StatifierPersistence.PinSource and delegates to count/2 from its own pins/2.

A source that cannot answer raises

StatifierPersistence.PinSource makes raising the way to say "I could not answer", because a source that answers zero when it does not know retires a pinned chart. This one keeps that: a context without :execution_ids, or a configuration that is not a %StatifierRouter.Config{}, raises rather than counting nothing, and StatifierPersistence.PinSource.collect/3 turns the raise into {:error, {module, {:raised, exception}}}. A read that the repo itself refuses raises for the same reason and reaches the caller the same way.