Layer 1 complete: E3-E6 + E2 analysis add-ons

Finishes the Layer 1 analytical core. All six experiments run with honest,
publication-quality figures; 71 tests green.

- E3 region-matched grounding: `grounding.exercised` knob + per-region tail
  survival. Matched holds the exercised region's tail (0.49) where uniform
  spreads thin and lets it collapse (0.07).
- E4 multi-teacher recombination: `run_coverage` runner. Union coverage matches
  U(K_T,rho,q) exactly. Finding: mean-mixture distillation shows NO surviving
  benefit (a conservation law — 1/K_T dilution cancels the union gain); a
  union-preserving max-merge (M2N2-style) does. E4 reports both operators.
- E5 QD vs greedy: greedy drives fixation (H~0.01); QD holds H at 0.48-0.88,
  rising with the novelty exponent.
- E6 re-mint gate: `arm` multi-override sweep. Re-minting a collapsed lineage
  locks in divergence of KL-to-original; gating on diversity prevents it.
- E2 analysis add-ons (from the companion work order, numbers verified): new
  analysis.py (reduce_to_stationary, critical_grounding with bootstrap CI ->
  g*=0.048, 95% CI [0.047,0.050]); tail_band_metrics + per-band logging; the
  E2 figure rebuilt as a 2x2 (defined g*+CI, g=0 flagged as a finite-time
  artifact, tail item-vs-mass, per-rarity-band panel). Uses truth-mass-weighted
  tail coverage rather than the raw (martingale) tail_mass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

results/E2/manifest.json

@@ -1,7 +1,7 @@
 {
   "experiment": "E2_grounding_phase_boundary",
   "master_seed": 20260704,
-  "git_commit": null,
+  "git_commit": "a6eb9b75124779375fa1a0b3a64115ecd705b218",
   "python": "3.14.5",
   "libraries": {
     "numpy": "2.5.0",
@@ -10,5 +10,5 @@
     "pyarrow": "24.0.0"
   },
   "rows": 400800,
-  "results_sha256": "863d9d0777db6916032ee34e8fe5651d24d86443dcd60de8d0da4220eb7625a3"
+  "results_sha256": "aa8633171f833611b9c2cde3d13c61e65a81a7c9c6cef5bc76a79127d8af59a3"
 }