RESULT 31: decoupling — tail win is 101% beta, centered CE-neutral at 42M tail; plain-full-epoch + 72M A/B queued post-crown; beta ablation auto-triggered

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014FAPDWQ49M5Ye3NpTndTpn

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diff --git a/docs/campaign/CASCADE_ABLATION_PLAN.md b/docs/campaign/CASCADE_ABLATION_PLAN.md
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@@ -568,6 +568,28 @@ direction), not training-under-fault; wave-2 = co-training with faults injected
 
 
 
+### RESULT 31 (2026-07-16): DECOUPLING VERDICT — the tail win is ALL beta; centered is CE-neutral at 42M tail. RESULT 22's mechanism reading corrected.
+The missing arms7 control (user-demanded): plain single-sided @ beta 3e-3 flat tail.
+| arm (45k->55k) | best | note |
+|---|---|---|
+| ctl (plain @1e-3) | 1.2678 | |
+| **arm_plain_f3e3 (plain @3e-3)** | **1.2590** | = centered to the 4th decimal |
+| arm_cent_f3e3 (centered @3e-3) | 1.2591 | |
+| arm_centmirror (mirror @3e-3) | 1.2590 | downstream parity of the mirror trick CONFIRMED |
+beta share of the tail effect: 101%. Readings:
+- RESULT 22's causal story ("O(beta^2) bias lets beta ride high") is REFUTED at this scale: plain
+  rides 3e-3 equally well. The O(beta) secant bias at 3e-3 is measurable in cos but COSTLESS in CE
+  — third independent confirmation that direction-space error does not price CE; only SNR does.
+- The zero-gap driver in stage1b_cent (1.2334) is therefore suspect of being pure-beta too:
+  **stage1b_plain3e3 full epoch queued** (post-crown, GPU1/3). If it lands ~1.233, the C512
+  zero-gap recipe simplifies to plain + big-beta = 1.0x cost, and centered/centfast/centmirror
+  demote to cos-telemetry tools pending a scale where bias binds.
+- 72M check queued (post-crown A/B): resume fw72m_cent s175000, 10k steps, centered-continue vs
+  plain-switch at identical schedule — decides whether the crown recipe needs centered at all.
+- Auto-triggered beta ablation RUNNING (share>=0.5 rule): plain @ {2e-3, 5e-3, 1e-2} + centered
+  @1e-2 — maps CE-vs-beta and where plain's O(beta) bias finally bites; 1e-2 arms double as
+  42M wall-2 probes (guard telemetry free).
+
 ### RESULT 30 (2026-07-16): QUANTIZATION Delta-vs-Delta MATRIX — equal at the operating point, EP-SPECIFIC tax below it.
 BP mirror suite complete (bp_qctl baseline 1.2171 — resumed-tail+amp beats the original fp32 twin,
 which is exactly why in-family baselines were required; user's methodology point vindicated).