test(cso): T6 — pin must-preserve security phrases (Phase A.5)

cso/SKILL.md is a content-heavy security audit skill (75 KB after T3+T4).
Codex 2nd-pass critique #9: "cso exemption too broad ... should still get
resolver dedup, catalog trim, sectioning if safe, and targeted evals
around must-not-miss checks."

T3 (jargon dedup) and T4 (catalog trim) already applied to cso the same
way they applied to every other skill — confirmed by inspection:
- jargon list NOT inlined (0 inline term lines)
- catalog description trimmed to one line (74 bytes vs 774 bytes baseline)
- "## When to invoke" body section present

T6 work: lock in the security-prose preservation via a gate-tier test
that fails CI if future compression strips load-bearing phrases:
- OWASP, STRIDE positioning
- daily / comprehensive mode discipline
- confidence scoring language
- active verification ("verif" prefix catches verify/verified/verification)
- ## Preamble heading (preamble resolver still fires)

Also guards cso against accidental over-stripping: SKILL.md must stay
≥30 KB (currently 75 KB) — a sudden cliff would mean compression went
past the targeted-dedup line into structural removal.

No structural change to cso. Future Phase B sections/ work for cso
requires writing baseline parity tests FIRST per the v2_PLAN.md
sequencing.

Test plan:
- bun test test/cso-preserved.test.ts: 5 pass

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/cso-preserved.test.ts

@@ -0,0 +1,86 @@
+/**
+ * cso security-guidance preservation test (v1.45.0.0 T6).
+ *
+ * The cso skill carries load-bearing security prose: OWASP Top 10 mappings,
+ * STRIDE threat-model phrasing, "do not auto-fix without user approval"
+ * gates. Codex 2nd-pass critique #9: "cso exemption too broad ... should
+ * still get resolver dedup, catalog trim, sectioning if safe, and targeted
+ * evals around must-not-miss checks."
+ *
+ * This test pins the must-not-miss checks. cso gets the same resolver gate
+ * (T2), jargon dedup (T3), and catalog trim (T4) as every other skill — but
+ * its security-guidance body content stays intact. Future compression work
+ * that would strip this content fails CI here.
+ */
+
+import { describe, test, expect } from 'bun:test';
+import * as fs from 'fs';
+import * as path from 'path';
+
+const REPO_ROOT = path.resolve(import.meta.dir, '..');
+const CSO_SKILL = path.join(REPO_ROOT, 'cso', 'SKILL.md');
+
+const MUST_PRESERVE_PHRASES = [
+  // OWASP / STRIDE positioning
+  'OWASP',
+  'STRIDE',
+  // Mode discipline
+  'daily',
+  'comprehensive',
+  // Severity language
+  'confidence',
+  // Active verification requirement (codex critique: "active verification")
+  'verif', // covers "verify", "verification", "verified"
+];
+
+const MUST_PRESERVE_HEADINGS = [
+  '## Preamble',  // from PREAMBLE resolver
+];
+
+describe('cso skill preserves load-bearing security guidance', () => {
+  test('cso/SKILL.md exists and is non-trivial', () => {
+    expect(fs.existsSync(CSO_SKILL)).toBe(true);
+    const content = fs.readFileSync(CSO_SKILL, 'utf-8');
+    // cso is a content-heavy security skill; under 30 KB suggests stripping went too far.
+    expect(content.length).toBeGreaterThan(30_000);
+  });
+
+  test('cso preserves required security phrases (case-insensitive)', () => {
+    const content = fs.readFileSync(CSO_SKILL, 'utf-8').toLowerCase();
+    const missing: string[] = [];
+    for (const phrase of MUST_PRESERVE_PHRASES) {
+      if (!content.includes(phrase.toLowerCase())) missing.push(phrase);
+    }
+    if (missing.length > 0) {
+      throw new Error(
+        `cso/SKILL.md is missing required security phrases: ${missing.join(', ')}. ` +
+        `These are load-bearing for the skill's audit posture. If you intentionally ` +
+        `removed them, update this test with the new phrasing.`,
+      );
+    }
+  });
+
+  test('cso preserves required headings', () => {
+    const content = fs.readFileSync(CSO_SKILL, 'utf-8');
+    for (const heading of MUST_PRESERVE_HEADINGS) {
+      expect(content).toContain(heading);
+    }
+  });
+
+  test('cso catalog trim landed (frontmatter description ≤ 200 chars)', () => {
+    const content = fs.readFileSync(CSO_SKILL, 'utf-8');
+    const fmMatch = content.match(/^---\n([\s\S]*?)\n---/);
+    expect(fmMatch).not.toBeNull();
+    const fm = fmMatch![1];
+    const descMatch = fm.match(/^description:\s+(.+)$/m);
+    expect(descMatch).not.toBeNull();
+    const desc = descMatch![1].trim();
+    expect(desc.length).toBeLessThanOrEqual(200);
+    expect(desc).toContain('(gstack)');
+  });
+
+  test('cso routing prose moved to "## When to invoke" body section', () => {
+    const content = fs.readFileSync(CSO_SKILL, 'utf-8');
+    expect(content).toContain('## When to invoke this skill');
+  });
+});