fix(dashboard): extract shared getBudgetSettings — single source of truth

Argus found getBudgetSettings() duplicated in CostPage and BudgetAlertBanner
with different implementations. Now extracted to utils/budgetSettings.ts:

- Single getBudgetSettings() with Number()/Boolean() coercion
- Single STORAGE_KEY constant ('aegis:settings')
- Both CostPage and BudgetAlertBanner import from shared module
- No more duplicate logic divergence risk

1265 tests pass, tsc clean, build clean.

Refs: #3183 (review)

Author: OneStepAt4time

dashboard/src/components/shared/BudgetAlertBanner.tsx

@@ -10,34 +10,14 @@
 import { useState, useEffect, useCallback } from 'react';
 import { AlertTriangle, X } from 'lucide-react';
 import { formatCurrency } from '../../utils/formatNumber';
-
-interface BudgetSettings {
-  budgetDailyCapUsd: number;
-  budgetMonthlyCapUsd: number;
-  budgetAlertEnabled: boolean;
-}
+import { getBudgetSettings } from '../../utils/budgetSettings';
 
 interface AlertState {
   level: 'warning' | 'critical';
   message: string;
   dismissed: boolean;
 }
 
-function getBudgetSettings(): BudgetSettings {
-  try {
-    const raw = localStorage.getItem('aegis:settings');
-    if (raw) {
-      const parsed = JSON.parse(raw);
-      return {
-        budgetDailyCapUsd: parsed.budgetDailyCapUsd ?? 0,
-        budgetMonthlyCapUsd: parsed.budgetMonthlyCapUsd ?? 0,
-        budgetAlertEnabled: parsed.budgetAlertEnabled ?? false,
-      };
-    }
-  } catch { /* ignore */ }
-  return { budgetDailyCapUsd: 0, budgetMonthlyCapUsd: 0, budgetAlertEnabled: false };
-}
-
 const DISMISS_KEY = 'aegis:budget-alert-dismissed';
 
 export function BudgetAlertBanner() {

dashboard/src/pages/CostPage.tsx

@@ -30,6 +30,7 @@ import type { AnalyticsCostsResponse } from '../types';
 import { BudgetProgressBar } from '../components/shared/BudgetProgressBar';
 import { SpendSummary } from '../components/cost/SpendSummary';
 import { ForecastChart } from '../components/cost/ForecastChart';
+import { getBudgetSettings, type BudgetSettings } from '../utils/budgetSettings';
 
 const MODEL_COLORS: Record<string, string> = {
   'claude-sonnet-4.6': 'var(--color-accent-cyan)',
@@ -63,27 +64,6 @@ function CustomTooltip({ active, payload, label }: {
 }
 
 
-interface BudgetSettings {
-  budgetDailyCapUsd: number;
-  budgetMonthlyCapUsd: number;
-  budgetAlertEnabled: boolean;
-}
-
-function getBudgetSettings(): BudgetSettings {
-  try {
-    const raw = localStorage.getItem('aegis:settings');
-    if (raw) {
-      const parsed = JSON.parse(raw);
-      return {
-        budgetDailyCapUsd: Number(parsed.budgetDailyCapUsd) || 0,
-        budgetMonthlyCapUsd: Number(parsed.budgetMonthlyCapUsd) || 0,
-        budgetAlertEnabled: Boolean(parsed.budgetAlertEnabled),
-      };
-    }
-  } catch { /* ignore parse errors */ }
-  return { budgetDailyCapUsd: 0, budgetMonthlyCapUsd: 0, budgetAlertEnabled: false };
-}
-
 
 interface BudgetOverviewProps {
   dailyData: Array<{ date: string; estimatedCostUsd: number; sessions: number }>;

dashboard/src/utils/budgetSettings.ts

@@ -0,0 +1,29 @@
+/**
+ * budgetSettings.ts — Shared budget settings reader from localStorage.
+ *
+ * Single source of truth for budget configuration parsing.
+ * Used by CostPage, BudgetAlertBanner, and any future budget-aware components.
+ */
+
+export interface BudgetSettings {
+  budgetDailyCapUsd: number;
+  budgetMonthlyCapUsd: number;
+  budgetAlertEnabled: boolean;
+}
+
+const STORAGE_KEY = 'aegis:settings';
+
+export function getBudgetSettings(): BudgetSettings {
+  try {
+    const raw = localStorage.getItem(STORAGE_KEY);
+    if (raw) {
+      const parsed = JSON.parse(raw);
+      return {
+        budgetDailyCapUsd: Number(parsed.budgetDailyCapUsd) || 0,
+        budgetMonthlyCapUsd: Number(parsed.budgetMonthlyCapUsd) || 0,
+        budgetAlertEnabled: Boolean(parsed.budgetAlertEnabled),
+      };
+    }
+  } catch { /* ignore parse errors */ }
+  return { budgetDailyCapUsd: 0, budgetMonthlyCapUsd: 0, budgetAlertEnabled: false };
+}