`BroadcastState.subs` stores each receiver's next unread deque
index, but `.statistics()` exposed that index as a queue length. A
caught-up receiver looked correct by accident while every queued
count was one short.
Convert cursors to retained, receivable counts and clamp lagged
receivers to the current queue length. Also avoid deprecated
`trio.Event` truthiness when reporting waiter counts.
Cover caught-up, queued, lagged and real-event states using actual
broadcast sends and receives.
Prompt-IO: ai/prompt-io/opencode/20260812T012324Z_06c4af17_prompt_io.md
(this patch was generated in some part by `opencode` using `gpt-5.6-sol` (`openai`))
Gud Boi