bench: orchestrate a multi-card campaign without touching the measurement path

campaign.sh fans a screened operator list across cards, one ab_repeat.sh per
card, serial within a card. It does no measuring: ab_repeat.sh is the path that
produced the four operator verdicts already on record, and it stays byte for
byte as it was.

Each card gets its own AB_ROOT. Eight ab_repeat.sh started in the same second
would otherwise compute the same timestamped directory name and two cards would
write into one.

ZL_ISOLATE_TUNER_CACHE=1 is forced, since eight processes on one sqlite is the
thing to avoid. The cost is that pinned configs differ from a shared-cache
batch, so absolute latencies cannot be quoted across the two; the caliber guard
refuses such comparisons on its own, which is why this is a note and not a
warning someone has to remember.

partition.py's shell output gained the per-card weight, because EXTRA_OPS has
to land on the lightest card and counting operators gets that wrong — one heavy
operator outweighs three light ones. It writes through stdout.buffer: Python
turns "\n" into CRLF on Windows, and the trailing \r then rides into the last
field and breaks the numeric comparison that picks the card.

ab_repeat.sh

@@ -42,7 +42,9 @@ if [[ -t 1 && -z "${NO_COLOR:-}" ]]; then
   export FLAGGEMS_PERF_COLOR=always
 fi
 
-ROOT="runs/ab_repeat_${SWITCH}_$(date +%Y%m%d-%H%M%S)"
+# AB_ROOT 供 campaign.sh 指定每卡独立的产物根：八个 ab_repeat.sh 同一秒启动时，
+# 默认的时间戳目录名会撞在一起，两张卡往同一个目录里写。
+ROOT="${AB_ROOT:-runs/ab_repeat_${SWITCH}_$(date +%Y%m%d-%H%M%S)}"
 mkdir -p "$ROOT"
 LOG="$ROOT/summary.log"
 STATUS="$ROOT/status.tsv"