Two tasks could receive through one `BroadcastReceiver` and race its
single `_wait_scope`. A later call could replace the scope, leaving
the first blocked through `.aclose()`.
Track the active `trio.lowlevel.Task` per receiver and reject an
overlapping call with `trio.BusyResourceError`. Include the owner's
task name and repr in the error, then clear ownership in `finally`.
Define each receiver as one logical subscription cursor. Concurrent
consumers must use separate `.subscribe()` receivers so each retains
an independent cursor and lag policy. Strict mode reads every retained
value or raises `Lagged`; `raise_on_lag=False` explicitly permits
drops.
Cover the regression with a checkpoint loop synchronized on
`recv_ready`; explain the interleaving inline, assert the error names
the active consumer, then release the source and prove the original
receive remains usable.
Prompt-IO: ai/prompt-io/opencode/20260828T014247Z_d06ee34b_prompt_io.md
(this patch was generated in some part by `opencode` using `gpt-5.6-sol` (`openai`))
Gud Boi