inspect() awaited an in-flight retirement drain unconditionally before entering
serialize(), so a slow drain pinned a cancelled inspect until it finished, past
the documented cancellation boundary. Race the retirement wait against the
signal with observeQueuedAbort, matching serialize()'s queued-read behaviour.
Adds a regression that cancels an inspect while a gated retirement is pending
and asserts prompt rejection without a backend read.
_Kerman
63c8494d69