CURRENT_TASK: Phase 72-2 complete (WarmPool sweep, all NO-GO, ENV knob ROI exhausted)

Phase 72-2 Results:
- WarmPool=16 (baseline): 56.23M ops/s
- WarmPool=20: 56.13M ops/s (-0.18%, NO-GO)
- WarmPool=24: 56.30M ops/s (+0.12%, noise)
- WarmPool=32: 56.07M ops/s (-0.28%, NO-GO)

Conclusion:
- ENV knob optimization exhausted
- WarmPool=16 remains optimal
- Next: Structural changes (Phase 74)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

docs/analysis/PHASE70_REFILL_OBSERVABILITY_PREREQS_SSOT.md

@@ -1,11 +1,12 @@
 # Phase 70: Refill Tuning Prerequisites (Observability SSOT)
 
-**Status**: 🟡 ACTIVE
+**Status**: ✅ COMPLETE (SSOT established)
 
 **Context**: 
 - Current baseline (Mixed WS=400 + prefault) generates almost **zero cache misses** (refills) in Unified Cache.
 - Optimizing `unified_cache_refill()` or Warm Pool logic will yield **zero throughput gain** if this path is not hot.
 - Phase 70 must be gated on *observing significant refill activity*.
+- Current conclusion (WS=400 SSOT): Refill/WarmPool-pop is **not hot** (misses are extremely low), so refill micro-optimizations are **frozen** for SSOT workloads; only research workloads should touch refill behavior.
 
 ## 1. Observability Protocol (Step 0)
 
@@ -53,6 +54,11 @@ HAKMEM_BENCH_PREFAULT=0 ./bench_random_mixed_hakmem_observe ...
 
 **WARNING**: Do NOT change `HAKMEM_TINY_STATIC_ROUTE` or `ULTRA` flags unless specifically testing routing changes. The default `LEGACY` route *does* use Unified Cache for alloc/free.
 
+**NOTE (Warm Pool sizing semantics)**:
+- `HAKMEM_WARM_POOL_SIZE` primarily controls the **registry-scan prefill cap** (`warm_pool_max_per_class()`).
+- The steady-state push-back cap inside `unified_cache_refill()` is `TinyClassPolicy.warm_cap` (typically 4/8), so
+  `HAKMEM_WARM_POOL_SIZE` only matters when registry scans/refills happen often enough to benefit from prefilled slabs.
+
 ## 3. Reference: Why "LEGACY" Route is OK
 
 - **LEGACY** route means "not ULTRA/MID/V7 specialized".
@@ -63,4 +69,4 @@ HAKMEM_BENCH_PREFAULT=0 ./bench_random_mixed_hakmem_observe ...
 Previous confusion ("LEGACY unused") was due to:
 1. Stats counting was gated by `#if !HAKMEM_BUILD_RELEASE`.
 2. Low miss rate in WS=400 made it look unused.
-3. Phase 70-0 fixed the stats visibility.
+3. Phase 70-0 fixed the stats visibility.