Preserve stable snapshots and stabilize Electron e2e (#734)

tests/unit/models-usage-history.test.ts

@@ -2,6 +2,8 @@ import { describe, expect, it } from 'vitest';
 import {
   filterUsageHistoryByWindow,
   groupUsageHistory,
+  resolveStableUsageHistory,
+  resolveVisibleUsageHistory,
   type UsageHistoryEntry,
 } from '@/pages/Models/usage-history';
 
@@ -65,4 +67,25 @@ describe('models usage history helpers', () => {
     expect(filtered).toHaveLength(2);
     expect(filtered.map((entry) => entry.totalTokens)).toEqual([12, 11]);
   });
+
+  it('clears the stable usage snapshot when a successful refresh returns empty', () => {
+    const stable = [createEntry(12, 12)];
+
+    expect(resolveStableUsageHistory(stable, [])).toEqual([]);
+  });
+
+  it('can preserve the last stable usage snapshot while a refresh is still in flight', () => {
+    const stable = [createEntry(12, 12)];
+
+    expect(resolveStableUsageHistory(stable, [], { preservePreviousOnEmpty: true })).toEqual(stable);
+  });
+
+  it('prefers fresh usage entries over the cached snapshot when available', () => {
+    const stable = [createEntry(12, 12)];
+    const fresh = [createEntry(13, 13)];
+
+    expect(resolveVisibleUsageHistory([], stable)).toEqual([]);
+    expect(resolveVisibleUsageHistory([], stable, { preferStableOnEmpty: true })).toEqual(stable);
+    expect(resolveVisibleUsageHistory(fresh, stable, { preferStableOnEmpty: true })).toEqual(fresh);
+  });
 });