Module retention 

Delivery-window retention (design: docs/mail4agent/messenger-model.md, “Server is a router”). The server is not an archive: a message event is only needed until every live device of every joined member has fetched it.

• record_device_ack — a /sync?since=s<N> proves the device holds every event up to stream id N (additive table device_acks).
• retention_report — how many message events a purge would drop.
• purge_delivered_events — drops them. NOT scheduled anywhere: the owner decides when to switch it on (it changes what /rooms/{id}/messages can return, see the design doc).

Only non-state events of CLOSED rooms are ever touched: plaintext public channels live in pub_events (crate::public_channels) and are excluded here by construction and by predicate. Only non-state events are ever touched. State, keys, membership and to-device queues are untouched here.

Structs

RetentionPolicy

Retention knobs.

RetentionReport

What a purge would do right now.

Constants

PURGE_BATCH

Most events one purge pass removes (keeps the DB lock short).

Functions

create_retention_schema

device_acks DDL. Called from init_messenger_db.

purge_delivered_events

Deletes eligible message events (and rows pointing at them). Returns how many events were removed.

record_device_ack

Records that device_id has received everything up to stream_id. Monotonic: an older token never moves the ack back.

retention_report

Counts message events and how many a purge would delete.