feat(app): daily budget alert (USD or token cap)

- Settings/General: Daily budget row (Off / USD amount / Tokens),
  positive-finite validation, warns at 80% and alerts at 100%
- app-wide one-line banner above every section: --warn at 80%+, --bad
  at 100%+, dismissible for the rest of the day
- USD caps compare raw USD against per-provider daily cost (works under
  any filter); token caps evaluate only on the all-providers view since
  provider-filtered history zeroes token fields (comparing against a
  false zero would always pass)

212/212, build green.

app/renderer/App.test.tsx

@@ -356,4 +356,51 @@ describe('App shortcuts', () => {
     expect(screen.getByRole('button', { name: /–/ })).toBeInTheDocument()
     expect(screen.getByText('30D')).not.toHaveClass('on')
   })
+
+  it('shows no daily budget banner when none is configured', async () => {
+    render(<App />)
+    expect(await screen.findByText('Most expensive sessions')).toBeInTheDocument()
+    expect(screen.queryByText(/daily budget/i)).not.toBeInTheDocument()
+  })
+
+  it('shows no banner when today spend is under 80% of the budget', async () => {
+    localStorage.setItem('codeburn.dailyBudget', JSON.stringify({ kind: 'usd', value: 100 }))
+    render(<App />)
+    expect(await screen.findByText('Most expensive sessions')).toBeInTheDocument()
+    expect(screen.queryByText(/daily budget/i)).not.toBeInTheDocument()
+  })
+
+  it('warns when today spend reaches 80% of the daily budget', async () => {
+    localStorage.setItem('codeburn.dailyBudget', JSON.stringify({ kind: 'usd', value: 14 }))
+    render(<App />)
+    // 12.34 / 14 = 88.1% → warning band
+    expect(await screen.findByText("Today's spend is at 88% of your daily budget")).toBeInTheDocument()
+  })
+
+  it('alerts and dismisses for the rest of the day when the budget is exceeded', async () => {
+    localStorage.setItem('codeburn.dailyBudget', JSON.stringify({ kind: 'usd', value: 10 }))
+    render(<App />)
+    expect(await screen.findByText('Daily budget exceeded: $12.34 of $10.00')).toBeInTheDocument()
+
+    fireEvent.click(screen.getByRole('button', { name: 'Dismiss' }))
+    await waitFor(() => expect(screen.queryByText(/Daily budget exceeded/)).not.toBeInTheDocument())
+    expect(localStorage.getItem('codeburn.dailyBudget.dismissed')).toBe(dateKey(new Date()))
+  })
+
+  it('evaluates a token budget only on the all-providers view', async () => {
+    const payload = overviewPayload()
+    payload.history.daily[0]!.inputTokens = 60_000
+    payload.history.daily[0]!.outputTokens = 40_000
+    mocks.getOverview.mockResolvedValue(payload)
+    localStorage.setItem('codeburn.dailyBudget', JSON.stringify({ kind: 'tokens', value: 90_000 }))
+    render(<App />)
+    expect(await screen.findByText('Daily budget exceeded: 100K of 90K')).toBeInTheDocument()
+
+    // A specific-provider filter zeroes history.daily token fields, so the token
+    // cap can no longer be evaluated: the banner must disappear.
+    fireEvent.click(screen.getByText('All providers'))
+    fireEvent.click(await screen.findByRole('option', { name: 'Claude' }))
+    await waitFor(() => expect(mocks.getOverview).toHaveBeenCalledWith('30days', 'claude'))
+    await waitFor(() => expect(screen.queryByText(/Daily budget exceeded/)).not.toBeInTheDocument())
+  })
 })

app/renderer/App.tsx

@@ -8,8 +8,10 @@ import { Sidebar, type Section } from './components/Sidebar'
 import { rangeLabel, TopBar } from './components/TopBar'
 import { Window } from './components/Window'
 import { usePolled } from './hooks/usePolled'
-import { formatUsd, setActiveCurrency } from './lib/format'
+import { readDailyBudget } from './lib/budget'
+import { formatCompact, formatUsd, setActiveCurrency } from './lib/format'
 import { codeburn } from './lib/ipc'
+import { localDateKey } from './lib/period'
 import { OverviewContent } from './sections/Overview'
 import { OptimizeContent } from './sections/Optimize'
 import { Models } from './sections/Models'
@@ -214,6 +216,7 @@ export function App() {
     <Window>
       <Sidebar active={section} onNavigate={navigate} status={<StatusLine polled={overview} />} />
       <div className="ct">
+        <DailyBudgetBanner payload={overview.data ?? null} provider={provider} />
         <ErrorBoundary key={section}>
         {section === 'plans' ? (
           <Plans period={period} refreshToken={refreshToken} onNavigate={navigate} />
@@ -291,3 +294,64 @@ function SectionPlaceholder({ title }: { title: string }) {
     </Panel>
   )
 }
+
+/** App-wide daily-budget alert: reads today's usage from the overview payload and
+ * warns at >=80% / alerts at >=100% of the configured cap. Dismissible per day. */
+function DailyBudgetBanner({ payload, provider }: { payload: MenubarPayload | null; provider: string }) {
+  const [, bumpDismiss] = useState(0)
+  const budget = readDailyBudget()
+  if (!budget || !payload) return null
+
+  // Token totals in history.daily are zeroed under a specific-provider filter
+  // (only cost is per-provider), so a token cap can only be evaluated honestly on
+  // the all-providers view; otherwise we'd compare usage against a false zero.
+  if (budget.kind === 'tokens' && provider !== 'all') return null
+
+  const todayKey = localDateKey(new Date())
+  let dismissed: string | null = null
+  try { dismissed = globalThis.localStorage?.getItem('codeburn.dailyBudget.dismissed') ?? null } catch { /* storage can be unavailable */ }
+  if (dismissed === todayKey) return null
+
+  // Today's entry may be absent when there has been no activity yet: that's 0 used.
+  const entry = payload.history.daily.find(day => day.date === todayKey)
+  const used = budget.kind === 'usd'
+    ? entry?.cost ?? 0
+    : entry ? entry.inputTokens + entry.outputTokens : 0
+  const percent = (used / budget.value) * 100
+  if (percent < 80) return null
+
+  const exceeded = percent >= 100
+  const accent = exceeded ? 'var(--bad)' : 'var(--warn)'
+  const spent = budget.kind === 'usd' ? formatUsd(used) : formatCompact(used)
+  const cap = budget.kind === 'usd' ? formatUsd(budget.value) : formatCompact(budget.value)
+  const text = exceeded
+    ? `Daily budget exceeded: ${spent} of ${cap}`
+    : `Today's spend is at ${Math.floor(percent)}% of your daily budget`
+
+  const dismiss = () => {
+    try { globalThis.localStorage?.setItem('codeburn.dailyBudget.dismissed', todayKey) } catch { /* storage can be unavailable */ }
+    bumpDismiss(tick => tick + 1)
+  }
+
+  return (
+    <div
+      role="status"
+      className="daily-budget-banner"
+      style={{
+        display: 'flex',
+        alignItems: 'center',
+        gap: 10,
+        padding: '6px 16px',
+        fontSize: 12,
+        fontWeight: 550,
+        color: accent,
+        borderLeft: `3px solid ${accent}`,
+        borderBottom: '1px solid var(--line)',
+        lineHeight: 1.4,
+      }}
+    >
+      <span style={{ flex: 1 }}>{text}</span>
+      <button type="button" className="set-text-button" style={{ color: 'var(--mut)' }} onClick={dismiss}>Dismiss</button>
+    </div>
+  )
+}

app/renderer/lib/budget.ts

@@ -0,0 +1,19 @@
+// Renderer-only daily budget setting (localStorage `codeburn.dailyBudget`).
+// A 'usd' cap is raw-USD (compared against history.daily cost, then displayed
+// via the currency-aware formatUsd); a 'tokens' cap counts input+output tokens.
+
+export type DailyBudget = { kind: 'usd' | 'tokens'; value: number }
+
+/** Parse the persisted budget, returning null when absent or malformed. */
+export function readDailyBudget(): DailyBudget | null {
+  let raw: string | null = null
+  try { raw = globalThis.localStorage?.getItem('codeburn.dailyBudget') ?? null } catch { return null }
+  if (!raw) return null
+  try {
+    const parsed = JSON.parse(raw) as Partial<DailyBudget>
+    if ((parsed.kind === 'usd' || parsed.kind === 'tokens') && typeof parsed.value === 'number' && Number.isFinite(parsed.value) && parsed.value > 0) {
+      return { kind: parsed.kind, value: parsed.value }
+    }
+  } catch { /* malformed JSON */ }
+  return null
+}

app/renderer/sections/Settings.test.tsx

@@ -114,6 +114,25 @@ describe('Settings', () => {
     expect(screen.queryByText('Claude config')).not.toBeInTheDocument()
   })
 
+  it('stores a positive daily budget from General', async () => {
+    const user = userEvent.setup()
+    render(<Settings period="month" />)
+    await user.click(screen.getByLabelText('Daily budget'))
+    await user.click(screen.getByRole('option', { name: 'USD amount' }))
+    await user.type(screen.getByLabelText('Daily budget amount'), '25')
+    expect(JSON.parse(localStorage.getItem('codeburn.dailyBudget')!)).toEqual({ kind: 'usd', value: 25 })
+  })
+
+  it('rejects a non-positive daily budget without persisting it', async () => {
+    const user = userEvent.setup()
+    render(<Settings period="month" />)
+    await user.click(screen.getByLabelText('Daily budget'))
+    await user.click(screen.getByRole('option', { name: 'Tokens' }))
+    await user.type(screen.getByLabelText('Daily budget amount'), '-5')
+    expect(screen.getByText('Enter a positive number.')).toBeInTheDocument()
+    expect(localStorage.getItem('codeburn.dailyBudget')).toBeFalsy()
+  })
+
   it('lists providers from the real overview payload', async () => {
     const user = userEvent.setup()
     render(<Settings period="week" />)

app/renderer/sections/Settings.tsx

@@ -7,6 +7,7 @@ import { Panel } from '../components/Panel'
 import { ProviderLogo } from '../components/ProviderLogo'
 import type { Section } from '../components/Sidebar'
 import { usePolled } from '../hooks/usePolled'
+import { readDailyBudget } from '../lib/budget'
 import { formatConverted, formatUsd } from '../lib/format'
 import { codeburn } from '../lib/ipc'
 import type { ActionResult, AliasRow, ClaudeConfigSelector, CliError, CombinedUsage, DeviceScanResult, Identity, JsonPlanSummary, MenubarPayload, Period, PlanId, PlanProvider, ShareStatus, StatusJson } from '../lib/types'
@@ -120,6 +121,9 @@ function GeneralPane({ period, refreshToken, claudeConfigs, claudeConfigSource }
     return saved === 'light' || saved === 'dark' ? saved : 'system'
   })
   const [defaultPeriod, setDefaultPeriod] = useState(() => readSetting('codeburn.defaultPeriod') ?? 'today')
+  const [budgetKind, setBudgetKind] = useState<'off' | 'usd' | 'tokens'>(() => readDailyBudget()?.kind ?? 'off')
+  const [budgetInput, setBudgetInput] = useState(() => { const budget = readDailyBudget(); return budget ? String(budget.value) : '' })
+  const [budgetError, setBudgetError] = useState('')
   const [message, setMessage] = useState<{ text: string; error: boolean } | null>(null)
 
   useEffect(() => {
@@ -127,6 +131,17 @@ function GeneralPane({ period, refreshToken, claudeConfigs, claudeConfigSource }
     else document.documentElement.setAttribute('data-theme', theme)
   }, [theme])
 
+  // Store on change; a positive finite amount persists, anything else clears the
+  // cap (so the banner turns off) and, when non-empty, flags a validation error.
+  const persistBudget = (kind: 'off' | 'usd' | 'tokens', input: string) => {
+    const trimmed = input.trim()
+    if (kind === 'off' || trimmed === '') { setBudgetError(''); writeSetting('codeburn.dailyBudget', ''); return }
+    const value = Number(trimmed)
+    if (!Number.isFinite(value) || value <= 0) { setBudgetError('Enter a positive number.'); return }
+    setBudgetError('')
+    writeSetting('codeburn.dailyBudget', JSON.stringify({ kind, value }))
+  }
+
   const chooseTheme = (next: Theme) => {
     setTheme(next)
     writeSetting('codeburn.theme', next)
@@ -165,6 +180,8 @@ function GeneralPane({ period, refreshToken, claudeConfigs, claudeConfigSource }
             <button className="set-text-button" onClick={() => void codeburn.resetCurrency().then(finishCurrency)}>Reset to USD</button>
           </span></div>
           <div className="about-row"><label className="tx" htmlFor="settings-period">Default period<small>Applied on next launch.</small></label><span className="r"><Dropdown id="settings-period" ariaLabel="Default period" value={defaultPeriod} options={[{ value: 'today', label: 'Today' }, { value: 'week', label: '7d' }, { value: '30days', label: '30d' }, { value: 'month', label: 'Month' }, { value: 'all', label: 'All' }]} onChange={value => { setDefaultPeriod(value); writeSetting('codeburn.defaultPeriod', value) }} width={92} /></span></div>
+          <div className="about-row"><label className="tx" htmlFor="settings-budget">Daily budget<small>Warns at 80%, alerts at 100%.</small></label><span className="r"><Dropdown id="settings-budget" ariaLabel="Daily budget" value={budgetKind} options={[{ value: 'off', label: 'Off' }, { value: 'usd', label: 'USD amount' }, { value: 'tokens', label: 'Tokens' }]} onChange={value => { const kind = value as 'off' | 'usd' | 'tokens'; setBudgetKind(kind); persistBudget(kind, budgetInput) }} width={120} />{budgetKind !== 'off' && <input className="set-input" type="text" inputMode="decimal" aria-label="Daily budget amount" placeholder={budgetKind === 'usd' ? 'USD' : 'tokens'} value={budgetInput} onChange={event => { setBudgetInput(event.target.value); persistBudget(budgetKind, event.target.value) }} style={{ width: 90 }} />}</span></div>
+          {budgetError && <p className="set-action-msg error">{budgetError}</p>}
           {message && <p className={message.error ? 'set-action-msg error' : 'set-action-msg'}>{message.text}</p>}
         </div>
       </div>