Paper A v13 rev9: sensitivity surface + honesty fixes (GPT-5.5 hostile review)

Pre-emptively address the three residual points from a hostile GPT-5.5
reviewer pass that rev8 had not fully closed (the rest of that review
matched the already-applied fusion revision):

- Sensitivity surface (Major 5): new Figure 6 maps the deployed rule over
  the full (cosine cut x dHash cut) plane - clean-group flag rate and the
  Firm A-minus-B/C/D contrast. Shows no cliff at (0.95, dHash<=5), contrast
  >45pp across a broad region (58pp at 0.97/dHash<=3), and that extending to
  the MC bound (dHash<=15) halves the contrast - so the thresholds are not
  cherry-picked and the weaker MC band is shown, not hidden. Reproducible
  via make_fig6_sensitivity.py (DB columns only).

- Soften "reuse-dominated" (Major 1): the assertion that Firm A "is" a
  reuse-dominated population now reads "behaves in the screen as," explicitly
  resting on interviews + byte-identity rather than per-signature ground
  truth; two other uses made conditional/generic.

- Shared-pipeline contamination of ICCR (Major 2): Sec III-E now names the
  shared within-firm imaging pipeline (scanners, PDF assembly, red-stamp
  removal) as a channel that can lift the inter-CPA rate above true chance,
  distinct from "shared template," supported by the Sec V-B pipeline audit;
  bias direction (higher floor) keeps the Firm-A contrast conservative.

rev9 docx rebuilt (6 figures embedded).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qn59FdF9JMyfFg3sjcUNNG

paper/v13_build/scripts/make_fig6_sensitivity.py

@@ -0,0 +1,61 @@
+"""Figure 6: two-measure sensitivity surface over the (cosine cut x dHash cut) plane.
+Panel A: clean-group (B/C/D) flag rate -- how permissive the operating point is.
+Panel B: Firm A minus B/C/D flag-rate contrast (pp) -- discrimination across the plane.
+Shows the chosen HC point (0.95, dHash<=5) is not a cherry-picked threshold and exposes
+the weaker MC band (dHash<=15). Reproduces from signature_analysis.db (DB columns only).
+"""
+import matplotlib
+matplotlib.use('Agg')
+import matplotlib.pyplot as plt
+import numpy as np
+import sqlite3
+
+DB = "/Volumes/NV2/PDF-Processing/signature-analysis/signature_analysis.db"
+BIG4 = ('勤業眾信聯合', '資誠聯合', '安侯建業聯合', '安永聯合')
+
+con = sqlite3.connect(DB); cur = con.cursor()
+cur.execute(f"""SELECT CASE WHEN excel_firm='勤業眾信聯合' THEN 1 ELSE 0 END isA,
+  max_similarity_to_same_accountant c, min_dhash_independent d
+FROM signatures WHERE is_valid=1 AND excel_firm IN ({','.join('?'*4)})
+  AND max_similarity_to_same_accountant IS NOT NULL AND min_dhash_independent IS NOT NULL""", BIG4)
+rows = cur.fetchall(); con.close()
+isA = np.array([r[0] for r in rows], bool)
+c = np.array([r[1] for r in rows]); d = np.array([r[2] for r in rows])
+cA, dA = c[isA], d[isA]; cB, dB = c[~isA], d[~isA]
+
+cos_cuts = np.arange(0.85, 0.9901, 0.0025)
+dh_cuts = np.arange(0, 21, 1)
+A = np.zeros((len(dh_cuts), len(cos_cuts)))
+B = np.zeros_like(A)
+for j, cc in enumerate(cos_cuts):
+    for i, dd in enumerate(dh_cuts):
+        A[i, j] = 100 * np.mean((cA > cc) & (dA <= dd))
+        B[i, j] = 100 * np.mean((cB > cc) & (dB <= dd))
+contrast = A - B
+
+extent = [cos_cuts[0], cos_cuts[-1], dh_cuts[0], dh_cuts[-1]]
+fig, axes = plt.subplots(1, 2, figsize=(10.5, 4.3))
+
+for ax, Z, title, cmap, lab in [
+    (axes[0], B, '(a) Clean group (B/C/D) flag rate', 'viridis', 'flag rate (%)'),
+    (axes[1], contrast, '(b) Firm A − B/C/D contrast', 'magma', 'contrast (pp)')]:
+    im = ax.imshow(Z, origin='lower', aspect='auto', extent=extent, cmap=cmap)
+    cb = fig.colorbar(im, ax=ax, pad=0.02); cb.set_label(lab, fontsize=8); cb.ax.tick_params(labelsize=7)
+    # operating points
+    ax.scatter([0.95], [5], marker='*', s=180, color='white', edgecolor='black', zorder=5,
+               label='HC operating point (0.95, dHash≤5)')
+    ax.axhline(15, color='white', ls=':', lw=1.0)
+    ax.text(0.853, 15.4, 'MC upper bound (dHash≤15)', color='white', fontsize=6.5, va='bottom')
+    ax.set_xlabel('cosine cut', fontsize=9)
+    ax.set_ylabel('dHash cut (≤)', fontsize=9)
+    ax.set_title(title, fontsize=9)
+    ax.tick_params(labelsize=7.5)
+    ax.legend(loc='lower left', fontsize=6.5, framealpha=0.85)
+
+fig.suptitle('Figure 6. Sensitivity surface of the deployed rule over the two-measure threshold plane (Big-4, n=%d).' % len(c),
+             fontsize=9, y=1.02)
+fig.tight_layout()
+out = '/Volumes/NV2/pdf_recognize/paper/v13_build/figures/fig6.png'
+fig.savefig(out, dpi=200, bbox_inches='tight')
+plt.close(fig)
+print(f"fig6 OK n={len(c)}; HC(0.95,5) contrast={contrast[5, np.argmin(abs(cos_cuts-0.95))]:.1f}pp; written {out}")