Module ring 

Per-topic ring buffer for captured events.

Each TopicRing is bounded in capacity. When a push would exceed capacity, the oldest event is evicted (FIFO). Cursors are server- assigned and strictly increasing for the life of the ring — a WS reconnect bumps the ring’s reset_epoch but never rewinds its cursors.

A ring’s first cursor is its base. The connector derives the base from the boot time (see connector::cursor_base), so a restarted process hands out cursors ABOVE anything the previous process did and a client holding an old cursor is never told “caught up” by a ring whose cursors restarted at 1 below it. When that cannot be guaranteed (a clock that went backwards), a cursor from the future is answered with ReadResult::CursorExpired rather than silence.

The ring is read by cursor: read_since(cursor, limit) returns events whose cursor is strictly greater than cursor, up to limit. If the caller’s cursor is older than the buffer’s current head (the smallest cursor still buffered), the read returns ReadResult::CursorExpired so the client can resync to head and emit a synthetic gap event.

Structs

TopicRing

FIFO ring of ObservedEvent keyed by cursor. Single owner; not Send + Sync on its own — wrap in Arc<RwLock<…>> for cross-task access.

Enums

ReadResult

Outcome of TopicRing::read_since.