bench harness: env-tunable vLLM health timeout + both-modes 5-policy driver

- b3_isolated_policy.sh: HEALTH_MAX_TRIES now env-overridable (default 180 ->
  360s unchanged); slow-node launches can pass HEALTH_MAX_TRIES=300 (600s) to
  ride out a single-instance startup flake without aborting the whole arm.
- run_5policy_both_modes.sh: runs run_5policy_600s.sh twice on the SAME ttp
  trace with REPLAY_DISPATCH_MODE={tracets,thinktime}, so the only variable is
  dispatch mode. Outputs to outputs/policy5_600s_{mode}_<date>/.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/b3_isolated_policy.sh

@@ -126,8 +126,9 @@ done
 echo "[isolated] waiting for vLLM health ..."
 # NIXL init takes ~100-150s per instance even with concurrent launches;
 # Mooncake is closer to ~30-60s. Use a generous 360s timeout to cover
-# both (90s -> 360s vs the previous 180s).
-HEALTH_MAX_TRIES=180
+# both (90s -> 360s vs the previous 180s). Override via env for slow nodes
+# (e.g. HEALTH_MAX_TRIES=300 -> 600s).
+HEALTH_MAX_TRIES="${HEALTH_MAX_TRIES:-180}"
 for i in $(seq 0 $((N_INSTANCES - 1))); do
     port=$((BASE_PORT + i))
     tries=0