The previous priority-then-round-robin shape applied the rotating
start-index globally over the sorted list, so the cross-tier order
flipped on alternate drains: drain N had high-priority first, drain
N+1 advanced streamRoundRobinStart and had low-priority first. The
priority hint was silently defeated under any sustained traffic.
Replace it with strict priority across tiers + round-robin only
within each same-priority tier. Higher tiers always drain ahead of
lower ones; same-priority peers continue to take turns via the
existing rotating start. Default-priority callers see no behaviour
change (single tier, identical rotation semantics).
Tighten the test: drain twice and assert the higher-priority stream
emits first on BOTH drains — the regression case that the single-
drain version of the test missed. Add a regression guard for the
same-priority round-robin so a future refactor can't silently
serialise on the first stream.
https://claude.ai/code/session_01KWdr4RjVvyYZfEuPVaQfUa
Claude
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