item 18 scored (uniform-depth collapse, CE depth-flatness mechanism); item 19 E1b pre-registered

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

results-loop/PROTOCOL_UNIFIED.md

@@ -383,3 +383,28 @@ is fully supported.
     arm (lambda=1e-3, seed 1) is added for immediate seed replication of
     the expected-winner penalty. Spark's queued gate jobs will be dropped
     to avoid duplication. Everything else per registration.
+
+--- Outcome, item 18 (scored 2026-07-16 ~00:40): predictions (b), (c)
+REFUTED, (a) marginal miss, (d) trivial pass. All arms converge to
+UNIFORM depth (lambda 0/1e-3/1e-2 -> E[k] 4/2-or-4/1; the two 1e-3 seeds
+picked different plateaus — degenerate penalty landscape), r = 0.000
+everywhere. Mechanism identified and consistent with prior findings:
+teacher-forced CE is depth-flat (stationarity), so CE provides no
+per-item depth gradient; the penalty alone cannot teach selectivity.
+The state DOES carry the signal (E0 probe: train acc 1.0) — the failure
+is the training signal, not the representation. E1-as-designed is dead;
+kill criterion NOT fully triggered (E2 untested, and the mechanism
+points at a repair).
+
+19. **E1b: label-supervised halting head (pre-registered 2026-07-16
+    ~00:45, before running).** Freeze the curriculum merge (adapter_code
+    s0); train ONLY the halting head (BCE): target halt=0 at iterations
+    below the label's depth (easy->1, hard->4, per STaR label), halt=1 at
+    or above it. 300 steps, mixed batches, head-only params. Eval: gated
+    eval as item 18, n=250. Predictions: (a) r(k*, hard) > 0.5 (the head
+    is a trained difficulty classifier now); (b) easy >= 95% at k*=1
+    (near-E0's 97.5); (c) hard >= 35.7% (>= best uniform arm, via better
+    recall than E0's frozen probe: more than 18/28 hard items routed
+    deep); (d) overall >= 52.0 at E[k] <= 2.2. If (c) fails while (a,b)
+    hold, halting-head recall saturates at probe level and gate quality,
+    not gate training, is the binding constraint.