Fix NaN handling in pct function with tests

common/src/util/__tests__/db-health-alerts.test.ts

@@ -368,3 +368,34 @@ describe('evaluateBusyBackendRank', () => {
     expect(evaluateBusyBackendRank([])).toEqual({ breach: false, top: null })
   })
 })
+
+describe('evaluateStatCoverage percentage formatting', () => {
+  it('handles zero whole gracefully', () => {
+    const cov = evaluateStatCoverage(
+      coverageRow({ pgss_rows: 0, pgss_with_text: 0 }),
+    )
+    expect(cov.summary).toContain('0/0')
+    expect(cov.summary).toContain('0%')
+  })
+
+  it('formats normal percentages correctly', () => {
+    const cov = evaluateStatCoverage(
+      coverageRow({ pgss_rows: 200, pgss_with_text: 50 }),
+    )
+    expect(cov.summary).toContain('25%')
+  })
+
+  it('rounds percentages correctly', () => {
+    const cov = evaluateStatCoverage(
+      coverageRow({ pgss_rows: 300, pgss_with_text: 100 }),
+    )
+    expect(cov.summary).toContain('33%')
+  })
+
+  it('handles 100% correctly', () => {
+    const cov = evaluateStatCoverage(
+      coverageRow({ pgss_rows: 100, pgss_with_text: 100 }),
+    )
+    expect(cov.summary).toContain('100%')
+  })
+})

common/src/util/db-health-alerts.ts

@@ -292,8 +292,10 @@ export function evaluateStatCoverage(row: StatCoverageRow): StatCoverage {
   // may break the alert that does not consult it.
   const statementsBlind = statementRows === 0
   const activityBlind = activityVisible === 0
-  const pct = (part: number, whole: number) =>
-    whole > 0 ? Math.round((part / whole) * 100) : 0
+  const pct = (part: number, whole: number) => {
+    if (!Number.isFinite(part) || !Number.isFinite(whole) || whole <= 0) return 0
+    return Math.round((part / whole) * 100)
+  }
   const summary = row.has_read_all_stats
     ? `role ${row.role} has pg_read_all_stats: full fleet visibility`
     : `role ${row.role} lacks pg_read_all_stats — ${statementsWithText}/${statementRows} ` +