PipePair has no continuous read pump — the test thread drains the pipe only
while it sits in ReadUntilAsync — so multi-megabyte DrainEvents frames
interleaved with the heartbeat loop wedge both ends inside FlushFileBuffers,
each waiting for the other to read. Negotiate a 128 KiB frame maximum instead:
the 10,000 byte-heavy events still overflow it many times over, so every
assertion (bounded reply, reported truncation, no event loss across repeated
drains, surviving session) is unchanged.
Joseph Doherty
7c2eaf09e2