diff --git a/web/scripts/__tests__/check-governance-health.test.ts b/web/scripts/__tests__/check-governance-health.test.ts
index 09cbaf55..64b0c0a0 100644
--- a/web/scripts/__tests__/check-governance-health.test.ts
+++ b/web/scripts/__tests__/check-governance-health.test.ts
@@ -1,4 +1,5 @@
 import { describe, it, expect } from 'vitest';
+import { computeGini, percentile } from '../../shared/governance-snapshot';
 import type {
   ActivityData,
   Comment,
@@ -9,7 +10,6 @@ import {
   buildHealthReport,
   computeCrossRoleReviewRate,
   computeDataWindowDays,
-  computeGini,
   computeMergeBacklogDepth,
   computeMergeLatency,
   computeContestedRate,
@@ -20,7 +20,6 @@ import {
   extractRole,
   hadQuorumFailure,
   inferEligibleVoterCount,
-  percentile,
   resolveActivityFile,
 } from '../check-governance-health';
 
diff --git a/web/scripts/check-governance-health.ts b/web/scripts/check-governance-health.ts
index 91a32932..646cb4f0 100644
--- a/web/scripts/check-governance-health.ts
+++ b/web/scripts/check-governance-health.ts
@@ -21,6 +21,7 @@
 import { existsSync, readFileSync } from 'node:fs';
 import { dirname, join, resolve } from 'node:path';
 import { fileURLToPath } from 'node:url';
+import { computeGini, percentile } from '../shared/governance-snapshot';
 import type {
   ActivityData,
   Comment,
@@ -156,33 +157,6 @@ export function extractRole(login: string): string | null {
   return match ? match[1] : null;
 }
 
-/**
- * Compute the p-th percentile of a pre-sorted ascending array.
- * Returns null for empty arrays.
- */
-export function percentile(sorted: number[], p: number): number | null {
-  if (sorted.length === 0) return null;
-  const index = Math.ceil((p / 100) * sorted.length) - 1;
-  return sorted[Math.max(0, index)];
-}
-
-/**
- * Compute the Gini coefficient for an array of non-negative values.
- * Returns 0 for arrays of length ≤ 1 or all-zero arrays.
- */
-export function computeGini(values: number[]): number {
-  if (values.length <= 1) return 0;
-  const sorted = [...values].sort((a, b) => a - b);
-  const n = sorted.length;
-  const total = sorted.reduce((a, b) => a + b, 0);
-  if (total === 0) return 0;
-  let sumOfDiffs = 0;
-  for (let i = 0; i < n; i++) {
-    sumOfDiffs += (2 * (i + 1) - n - 1) * sorted[i];
-  }
-  return sumOfDiffs / (n * total);
-}
-
 // ──────────────────────────────────────────────
 // Metric computation
 // ──────────────────────────────────────────────
diff --git a/web/shared/__tests__/governance-snapshot.test.ts b/web/shared/__tests__/governance-snapshot.test.ts
index 4474390c..38041603 100644
--- a/web/shared/__tests__/governance-snapshot.test.ts
+++ b/web/shared/__tests__/governance-snapshot.test.ts
@@ -7,6 +7,8 @@ import {
   buildGovernanceHistoryArtifact,
   parseGovernanceHistoryArtifact,
   serializeGovernanceHistoryForIntegrity,
+  percentile,
+  computeGini,
   type GovernanceSnapshot,
 } from '../governance-snapshot';
 import type { ActivityData, Proposal, AgentStats } from '../types';
@@ -356,3 +358,57 @@ describe('governance history artifact', () => {
     expect(decoded.schemaVersion).toBe(GOVERNANCE_HISTORY_SCHEMA_VERSION);
   });
 });
+
+// ──────────────────────────────────────────────
+// percentile
+// ──────────────────────────────────────────────
+
+describe('percentile', () => {
+  it('returns null for empty array', () => {
+    expect(percentile([], 50)).toBeNull();
+  });
+
+  it('returns single element for any percentile', () => {
+    expect(percentile([100], 50)).toBe(100);
+    expect(percentile([100], 95)).toBe(100);
+  });
+
+  it('computes median of sorted array', () => {
+    expect(percentile([10, 20, 30, 40, 50], 50)).toBe(30);
+  });
+
+  it('computes p95 of sorted array', () => {
+    const sorted = [1, 2, 3, 4, 5, 6, 7, 8, 9, 100];
+    expect(percentile(sorted, 95)).toBe(100);
+  });
+});
+
+// ──────────────────────────────────────────────
+// computeGini
+// ──────────────────────────────────────────────
+
+describe('computeGini', () => {
+  it('returns 0 for empty or single-element array', () => {
+    expect(computeGini([])).toBe(0);
+    expect(computeGini([10])).toBe(0);
+  });
+
+  it('returns 0 for perfectly equal distribution', () => {
+    expect(computeGini([5, 5, 5, 5])).toBe(0);
+  });
+
+  it('returns 0 for all-zero values', () => {
+    expect(computeGini([0, 0, 0])).toBe(0);
+  });
+
+  it('returns near 1 for maximum concentration', () => {
+    const gini = computeGini([0, 0, 0, 100]);
+    expect(gini).toBeGreaterThan(0.7);
+  });
+
+  it('returns a value between 0 and 1 for mixed distribution', () => {
+    const gini = computeGini([10, 20, 30, 40]);
+    expect(gini).toBeGreaterThan(0);
+    expect(gini).toBeLessThan(1);
+  });
+});
diff --git a/web/shared/governance-snapshot.ts b/web/shared/governance-snapshot.ts
index 97e06ae8..2a52e916 100644
--- a/web/shared/governance-snapshot.ts
+++ b/web/shared/governance-snapshot.ts
@@ -432,6 +432,16 @@ function computeConsensusScore(proposals: Proposal[]): number {
   return Math.min(25, voteScore + diversityScore + discussionScore);
 }
 
+/**
+ * Compute the p-th percentile of a pre-sorted ascending array.
+ * Returns null for empty arrays.
+ */
+export function percentile(sorted: number[], p: number): number | null {
+  if (sorted.length === 0) return null;
+  const index = Math.ceil((p / 100) * sorted.length) - 1;
+  return sorted[Math.max(0, index)];
+}
+
 /** Gini coefficient for distribution analysis. Returns 0-1. */
 export function computeGini(values: number[]): number {
   if (values.length <= 1) return 0;