Gate finding BN10.r1.2c (Low): the inline re-entrant branch appended the
nested ctx to the outer load's scope and never removed it, so a nested
load that had already finished (and was recorded enabled under its own
key) got fenced by _abandon_load() when the outer load later timed out.
Keep the ctx in scope only while its fn() runs.
The kept nested-inline test now times the outer load out with one finished
and one hung nested load, asserting only outer + hung are abandoned; this
also pins the nested-abandon behaviour of the previous commit.
f7bbbc474e