Function subscribed_feed_ids 

pub async fn subscribed_feed_ids(
    pool: &SqlitePool,
    did: &str,
) -> Result<Vec<i64>>

The feed ids a did currently subscribes to (its sub_ref rows). Bounded by the per-DID subscription cap, so callers can safely iterate it — e.g. the global “mark all read” path fans out over feeds (bounded) rather than over unread entries (unbounded).