Engine-state ablation: full sweep harness + results

Real-time engine state is NOT the routing lever. Across 6 policies × es0/es1,
real state reshuffles 44-76% of decisions but never beats the champion
(unified+A+B, p90 7.62s). The effect's SIGN is set by reactivity: one-shot
placement (sticky) HELPS -26%; per-request affinity-dominated is a wash;
per-request pure-load (lmetric +17%, load_only +27%) HURTS via herding (stale
shadow was a dampener). Feed verified fresh (median 25ms, <=92ms during
prefills). Prior shadow-state results stand. ES_ABLATION_RESULTS.md has the
table + mechanism; run_full_ablation.sh / fresh_sampler.py / cmp_es.py are the
harness.

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

microbench/connector_tax/layerwise/fresh_sampler.py

@@ -0,0 +1,30 @@
+#!/usr/bin/env python3
+"""Sample engine-state feed freshness during the es1 run.
+Writes one jsonl record per engine per tick: age_s = now - state.ts.
+Stops when the DONE marker appears (run finished + /dev/shm wiped) or after 90min.
+"""
+import json, os, time, sys, glob
+
+esdir, outpath, donemarker = sys.argv[1], sys.argv[2], sys.argv[3]
+deadline = time.time() + 90 * 60
+with open(outpath, "a") as out:
+    while not os.path.exists(donemarker) and time.time() < deadline:
+        now = time.time()
+        if os.path.isdir(esdir):
+            for f in sorted(glob.glob(os.path.join(esdir, "engine_*.json"))):
+                try:
+                    s = json.load(open(f))
+                    rec = {
+                        "now": round(now, 3),
+                        "engine": os.path.basename(f)[:-5],
+                        "age_s": round(now - s.get("ts", 0), 4),
+                        "num_running": s.get("num_running"),
+                        "num_prefilling": s.get("num_prefilling"),
+                        "max_prefill_remaining": s.get("max_prefill_remaining"),
+                        "kv_used": s.get("gpu_kv_used_frac"),
+                    }
+                    out.write(json.dumps(rec) + "\n")
+                except Exception:
+                    pass
+            out.flush()
+        time.sleep(5)