chore(soak): re-scope nightly soak 500->200 rps (measured sustainable) + fix image drift

500 rps failed the capacity gate every night (peach mix is write-heavy; the
write path is structurally capped on 3-node RF3 full placement). A settled-
cluster capacity sweep measured the mix clean (0.00% error, 0 follower
restarts) at 100/150/200/250 rps; set the nightly target to 200 rps with margin
for a 1h x 30-night endurance run. SLO gates unchanged.

Also fix the image drift: the manifest pinned stress:m12-soak-eval (never
pushed -> ImagePull NotFound), while the live cronjob already ran the pullable
stress:m12-rc7-seedretry. The manifest now matches the live, pullable image.

tidal-stress/k8s/soak-nightly-cronjob.yaml

@@ -22,12 +22,17 @@
 # The streak passes when 30 CONSECUTIVE nightly Jobs have exited 0 with zero
 # under-load pod restarts (the monitor records restarts; see soak-monitor.yaml).
 #
-# SUSTAINED RATE: 500 rps mixed (peach: feed/search/view/like/skip/item/embed) —
-# deliberately BELOW the SLA knee. The rc12 read-SLA gate sustained 500 rps at
-# p99 9.28ms / recall 0.9989 / 0% err / 0 under-load restarts, so 500 rps is a
-# safe endurance rate that exercises BOTH read and write paths without parking
-# the cluster at its ceiling (a soak proves stability over time, not peak — the
-# 1-hour 100k-DAU peak run is the separate `--ramp 3900:3600` throughput gate).
+# SUSTAINED RATE: 200 rps mixed (peach: feed/search/view/like/skip/item/embed).
+# RE-SCOPED 2026-06-19 from 500 rps. The original 500 rps cited the rc12 READ-SLA
+# gate, but the peach mix is WRITE-heavy (view/like/skip ≈ 90% of ops) and the
+# write path is structurally capped on this 3-node RF3 full-placement cluster
+# (every follower applies every 1536-D write; T5). At 500 rps the soak FAILED
+# every night (2026-06-17/18/19: p99 198-305ms, error 12-33%). A 2026-06-19
+# capacity sweep on a settled cluster measured the peach mix CLEAN (0.00% error,
+# p99 schedule-lag <5ms, 0 follower restarts) at 100/150/200/250 rps; the knee is
+# between 250 and 500. 200 rps is the measured sustainable rate with margin for a
+# 1-hour × 30-consecutive-night endurance run. Raise only with more write capacity
+# (≥5 nodes / partitioned placement) — see orchard9-k3sf cluster-state.yaml.
 #
 # WHY A CRONJOB, NOT ONE LONG JOB: the GA bar is literally "30 CONSECUTIVE DAYS"
 # of an independent nightly verdict — a CronJob produces exactly that audit trail
@@ -82,7 +87,7 @@ spec:
               type: RuntimeDefault
           containers:
             - name: soak
-              image: registry.threesix.ai/tidal/stress:m12-soak-eval
+              image: registry.threesix.ai/tidal/stress:m12-rc7-seedretry
               imagePullPolicy: IfNotPresent
               # entrypoint is tidal-stress; wrap it so we can stamp the result file
               # name with the date and append a ledger line regardless of verdict.
@@ -92,7 +97,7 @@ spec:
                   set -u
                   DATE="$(date -u +%Y-%m-%d)"
                   OUT="/results/soak-$DATE.json"
-                  echo "soak $DATE start $(date -u +%H:%M:%SZ) target=cluster image=m12-soak-eval"
+                  echo "soak $DATE start $(date -u +%H:%M:%SZ) target=cluster image=m12-rc7-seedretry-200rps"
                   tidal-stress \
                     --target https://tidaldb-0.tidaldb-peers.tidaldb-cluster.svc.cluster.local:9500 \
                     --target https://tidaldb-1.tidaldb-peers.tidaldb-cluster.svc.cluster.local:9500 \
@@ -103,7 +108,7 @@ spec:
                     --embedding-dim 1536 \
                     --mix peach \
                     --users 50000 \
-                    --ramp "500:3600" \
+                    --ramp "200:3600" \
                     --json-summary "$OUT" \
                     --max-p99-ms 150 \
                     --max-error-pct 1 \
@@ -120,7 +125,7 @@ spec:
                   PASSED="$(grep -o '"passed"[: ]*[a-z]*' "$OUT" 2>/dev/null | head -1 | grep -o '[a-z]*$')"
                   P99="$(grep -o '"overall_p99_ms"[: ]*[0-9.]*' "$OUT" 2>/dev/null | tail -1 | grep -o '[0-9.]*$')"
                   ERRF="$(grep -o '"error_rate"[: ]*[0-9.]*' "$OUT" 2>/dev/null | tail -1 | grep -o '[0-9.]*$')"
-                  printf '%s\t%s\trc=%s\tpassed=%s\tp99_ms=%s\terr_frac=%s\timage=m12-soak-eval\n' \
+                  printf '%s\t%s\trc=%s\tpassed=%s\tp99_ms=%s\terr_frac=%s\timage=m12-rc7-seedretry-200rps\n' \
                     "$DATE" "$VERD" "$RC" "${PASSED:-?}" "${P99:-?}" "${ERRF:-?}" >> /results/ledger.tsv
                   echo "soak $DATE end $(date -u +%H:%M:%SZ) verdict=$VERD rc=$RC p99=${P99:-?} err=${ERRF:-?}"
                   # Refresh the streak immediately, CONSULTING restarts.tsv: a night