neural: grounding refinement + all five Layer-1.5 figures

Grounding refinement (18 reps): forward-KL is the operative neural
collapse metric, not H or tail-survival. The RNN's smoothing keeps
spurious tail modes alive, so tail_truth_mass_alive is flat/non-monotone
in g and H stays ~0.8 of H*; only forward-KL falls monotonically (dry
2.08 -> g=0.2: 0.75, paired t up to 3.3). The sharp g* << 1 is an
exact-operator feature carried by the histogram bridge (0.047); the
trained RNN confirms the SIGN and softens the sharpness (half the KL gap
closes by g~0.04, but full recovery needs g~0.19). Blueprint 3.5's
directional claim holds; the pre-registered 95%-of-H*/tail falsifier is
not met because those are the wrong metrics for a smoothing model.

Robustness: a fully-degenerate RNN can emit only invalid codewords, so
measure_distribution now returns a terminal-collapse sentinel (fixation
on the dominant mode) instead of crashing a long sweep. Edge test added
(94 tests green).

Figures: plot_{bridge,collapse,grounding,architectures,recombination}.py,
each a pure function of its committed bundle, wired into `make figures`
(glob plot_*.py minus plot_E[1-6]/_*). bridge sits on the exact H_eq
curve (g*=0.047); recombination shows max-merge rising while mean-distill
stays flat; architectures shows the collapse/rescue signs across
histogram/GRU/MLP.

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

results/grounding/resolved_config.yaml

@@ -1,11 +1,11 @@
 experiment: grounding_phase_boundary
 seed: 20260704
-n_replicates: 5
+n_replicates: 18
 source_config:
   experiment: grounding_phase_boundary
   kind: gen_lineage
   seed: 20260704
-  n_replicates: 5
+  n_replicates: 18
   generations: 30
   synthetic:
     K: 256
@@ -25,7 +25,7 @@ source_config:
     epochs: 25
     lr: 0.002
     batch_size: 256
-    n_eval: 12000
+    n_eval: 15000
   dynamics:
     n: 200
     grounding:
@@ -45,7 +45,9 @@ source_config:
     - 0.005
     - 0.01
     - 0.02
+    - 0.035
     - 0.05
+    - 0.075
     - 0.1
     - 0.2
   output:
@@ -73,7 +75,7 @@ grid:
       epochs: 25
       lr: 0.002
       batch_size: 256
-      n_eval: 12000
+      n_eval: 15000
     dynamics:
       n: 200
       grounding:
@@ -109,7 +111,7 @@ grid:
       epochs: 25
       lr: 0.002
       batch_size: 256
-      n_eval: 12000
+      n_eval: 15000
     dynamics:
       n: 200
       grounding:
@@ -145,7 +147,7 @@ grid:
       epochs: 25
       lr: 0.002
       batch_size: 256
-      n_eval: 12000
+      n_eval: 15000
     dynamics:
       n: 200
       grounding:
@@ -181,7 +183,7 @@ grid:
       epochs: 25
       lr: 0.002
       batch_size: 256
-      n_eval: 12000
+      n_eval: 15000
     dynamics:
       n: 200
       grounding:
@@ -195,6 +197,42 @@ grid:
     metrics:
       kl_floor: 1.0e-09
       support_eps: 1.0e-09
+- label:
+    g: 0.035
+    m: 7
+  neural_cfg:
+    synthetic:
+      K: 256
+      R: 1
+      tail: zipf
+      zipf_s: 1.3
+      tail_frac: 0.5
+      tail_threshold: 0.001
+      init: truth
+      style_len: 3
+      style_vocab: 5
+      id_base: 2
+    model:
+      kind: rnn
+      hidden: 128
+      embed: 24
+      epochs: 25
+      lr: 0.002
+      batch_size: 256
+      n_eval: 15000
+    dynamics:
+      n: 200
+      grounding:
+        m: 7
+        policy: proportional
+      remint:
+        enabled: false
+        period: null
+        H_gate: null
+    generations: 30
+    metrics:
+      kl_floor: 1.0e-09
+      support_eps: 1.0e-09
 - label:
     g: 0.05
     m: 11
@@ -217,7 +255,7 @@ grid:
       epochs: 25
       lr: 0.002
       batch_size: 256
-      n_eval: 12000
+      n_eval: 15000
     dynamics:
       n: 200
       grounding:
@@ -231,6 +269,42 @@ grid:
     metrics:
       kl_floor: 1.0e-09
       support_eps: 1.0e-09
+- label:
+    g: 0.075
+    m: 16
+  neural_cfg:
+    synthetic:
+      K: 256
+      R: 1
+      tail: zipf
+      zipf_s: 1.3
+      tail_frac: 0.5
+      tail_threshold: 0.001
+      init: truth
+      style_len: 3
+      style_vocab: 5
+      id_base: 2
+    model:
+      kind: rnn
+      hidden: 128
+      embed: 24
+      epochs: 25
+      lr: 0.002
+      batch_size: 256
+      n_eval: 15000
+    dynamics:
+      n: 200
+      grounding:
+        m: 16
+        policy: proportional
+      remint:
+        enabled: false
+        period: null
+        H_gate: null
+    generations: 30
+    metrics:
+      kl_floor: 1.0e-09
+      support_eps: 1.0e-09
 - label:
     g: 0.1
     m: 22
@@ -253,7 +327,7 @@ grid:
       epochs: 25
       lr: 0.002
       batch_size: 256
-      n_eval: 12000
+      n_eval: 15000
     dynamics:
       n: 200
       grounding:
@@ -289,7 +363,7 @@ grid:
       epochs: 25
       lr: 0.002
       batch_size: 256
-      n_eval: 12000
+      n_eval: 15000
     dynamics:
       n: 200
       grounding: