app: Download button direct-downloads the update asset

The update Download button opened the GitHub release page; it now
downloads the right artifact for the running platform directly: arm64
or x64 dmg on macOS (preload newly exposes process.arch), the Setup exe
on Windows. Linux keeps the release page since it ships three formats
and the user picks. Unknown platforms and preloads without arch fall
back to the page. URL mapping is unit-tested per platform.

app/electron/preload.ts

@@ -69,6 +69,7 @@ const bridge = {
     return () => { ipcRenderer.removeListener('codeburn:update', listener) }
   },
   platform: process.platform,
+  arch: process.arch,
 }
 
 contextBridge.exposeInMainWorld('codeburn', bridge)

app/renderer/components/AboutModal.tsx

@@ -3,7 +3,7 @@ import { useEffect, useState, type MouseEvent, type ReactNode } from 'react'
 import { version } from '../../package.json'
 import { FlameMark } from './FlameMark'
 import { BUILD_STAMP } from '../lib/build'
-import { releasePageUrl, useUpdateStatus } from '../hooks/useUpdateStatus'
+import { updateDownloadUrl, useUpdateStatus } from '../hooks/useUpdateStatus'
 import { codeburn } from '../lib/ipc'
 
 export type SocialLink = {
@@ -81,7 +81,7 @@ export function AboutModal({ socials, onClose }: { socials: SocialLink[]; onClos
                       <button
                         type="button"
                         className="set-text-button"
-                        onClick={() => { void codeburn.openExternal(releasePageUrl(status.tag!)) }}
+                        onClick={() => { void codeburn.openExternal(updateDownloadUrl(status.tag!)) }}
                       >
                         Download
                       </button>

app/renderer/components/UpdateBanner.tsx

@@ -1,6 +1,6 @@
 import { useState } from 'react'
 
-import { releasePageUrl, useUpdateStatus } from '../hooks/useUpdateStatus'
+import { updateDownloadUrl, useUpdateStatus } from '../hooks/useUpdateStatus'
 import { codeburn } from '../lib/ipc'
 
 const DISMISS_KEY = 'codeburn.updateDismissed'
@@ -32,7 +32,7 @@ export function UpdateBanner() {
     <div role="status" className="update-banner">
       <span>
         Update available: CodeBurn {status.latestVersion} ·{' '}
-        <button type="button" className="set-text-button" onClick={() => { void codeburn.openExternal(releasePageUrl(tag)) }}>Download</button>
+        <button type="button" className="set-text-button" onClick={() => { void codeburn.openExternal(updateDownloadUrl(tag)) }}>Download</button>
       </span>
       <button type="button" className="set-text-button" onClick={dismiss}>Dismiss</button>
     </div>

app/renderer/hooks/useUpdateStatus.test.ts

@@ -0,0 +1,44 @@
+import { describe, expect, it, vi } from 'vitest'
+
+vi.mock('../lib/ipc', () => ({
+  codeburn: { platform: 'linux', arch: 'x64' },
+}))
+
+import { directDownloadUrl, releasePageUrl, updateDownloadUrl } from './useUpdateStatus'
+
+const TAG = 'desktop-v0.9.19'
+const BASE = 'https://github.com/getagentseal/codeburn/releases/download/desktop-v0.9.19'
+
+describe('directDownloadUrl', () => {
+  it('maps macOS arm64 to the arm64 dmg', () => {
+    expect(directDownloadUrl(TAG, 'darwin', 'arm64')).toBe(`${BASE}/CodeBurn-0.9.19-arm64.dmg`)
+  })
+
+  it('maps macOS x64 to the plain dmg', () => {
+    expect(directDownloadUrl(TAG, 'darwin', 'x64')).toBe(`${BASE}/CodeBurn-0.9.19.dmg`)
+  })
+
+  it('maps Windows to the Setup exe regardless of arch', () => {
+    expect(directDownloadUrl(TAG, 'win32', 'x64')).toBe(`${BASE}/CodeBurn-Setup-0.9.19.exe`)
+    expect(directDownloadUrl(TAG, 'win32', undefined)).toBe(`${BASE}/CodeBurn-Setup-0.9.19.exe`)
+  })
+
+  it('returns null for Linux (three formats, the user picks on the page)', () => {
+    expect(directDownloadUrl(TAG, 'linux', 'x64')).toBeNull()
+  })
+
+  it('returns null for unknown platforms, missing mac arch, and foreign tags', () => {
+    expect(directDownloadUrl(TAG, 'freebsd', 'x64')).toBeNull()
+    expect(directDownloadUrl(TAG, 'darwin', undefined)).toBeNull()
+    expect(directDownloadUrl('mac-v0.9.19', 'darwin', 'arm64')).toBeNull()
+  })
+})
+
+describe('updateDownloadUrl fallback', () => {
+  it('falls back to the release page when no direct asset fits', () => {
+    // The mocked bridge reports linux, where no single asset fits, so the
+    // click target is the release page.
+    expect(releasePageUrl(TAG)).toBe('https://github.com/getagentseal/codeburn/releases/tag/desktop-v0.9.19')
+    expect(updateDownloadUrl(TAG)).toBe(releasePageUrl(TAG))
+  })
+})

app/renderer/hooks/useUpdateStatus.ts

@@ -23,8 +23,35 @@ export function useUpdateStatus(): UpdateStatus | null {
   return status
 }
 
-/** GitHub release page for a desktop tag — the Download target (no site #get
- *  anchor exists). https-only, so it passes the openExternal allowlist. */
+/** GitHub release page for a desktop tag — the fallback Download target when
+ *  no single direct asset fits (Linux ships three formats) or the platform is
+ *  unknown. https-only, so it passes the openExternal allowlist. */
 export function releasePageUrl(tag: string): string {
   return `https://github.com/getagentseal/codeburn/releases/tag/${tag}`
 }
+
+/**
+ * Direct asset download for the running platform, so Download saves the file
+ * instead of landing on a GitHub page. Filenames mirror the electron-builder
+ * output (app/DISTRIBUTION.md) and are version-derived from the tag. Returns
+ * null (callers fall back to the release page) for Linux — three formats, the
+ * user picks — and for unknown platforms or a preload without `arch`.
+ */
+export function directDownloadUrl(tag: string, platform: string | undefined, arch: string | undefined): string | null {
+  const version = tag.startsWith('desktop-v') ? tag.slice('desktop-v'.length) : null
+  if (!version) return null
+  let file: string | null = null
+  if (platform === 'darwin') {
+    if (!arch) return null
+    file = arch === 'arm64' ? `CodeBurn-${version}-arm64.dmg` : `CodeBurn-${version}.dmg`
+  } else if (platform === 'win32') {
+    file = `CodeBurn-Setup-${version}.exe`
+  }
+  if (!file) return null
+  return `https://github.com/getagentseal/codeburn/releases/download/${tag}/${file}`
+}
+
+/** The Download click target: direct asset when determinable, else the page. */
+export function updateDownloadUrl(tag: string): string {
+  return directDownloadUrl(tag, codeburn.platform, codeburn.arch) ?? releasePageUrl(tag)
+}

app/renderer/lib/types.ts

@@ -592,6 +592,9 @@ export interface CodeburnBridge {
   getPlans(period: Period): Promise<StatusJson>
   getActReport(): Promise<ActReportJson>
   readonly platform: string
+  /** Node process.arch of the host ('arm64', 'x64', ...). Absent on preloads
+   *  that predate the direct-download update link. */
+  readonly arch?: string
   getModels(period: Period, provider: string, byTask: boolean, range?: DateRange): Promise<ModelReportRow[]>
   getSessions(period: Period, provider: string, range?: DateRange): Promise<SessionRow[]>
   getCompareModels(period: Period, provider: string): Promise<ModelStats[]>

app/renderer/sections/Settings.tsx

@@ -8,7 +8,7 @@ import { Panel } from '../components/Panel'
 import { ProviderLogo } from '../components/ProviderLogo'
 import type { Section } from '../components/Sidebar'
 import { usePolled } from '../hooks/usePolled'
-import { releasePageUrl, useUpdateStatus } from '../hooks/useUpdateStatus'
+import { updateDownloadUrl, useUpdateStatus } from '../hooks/useUpdateStatus'
 import { version as appVersion } from '../../package.json'
 import { readDailyBudget } from '../lib/budget'
 import { formatConverted, formatUsd } from '../lib/format'
@@ -208,7 +208,7 @@ function GeneralPane({ period, refreshToken, claudeConfigs, claudeConfigSource,
         </div>
         <div className="about-sec set-last-sec">
           <div className="about-sec-h">About</div>
-          <div className="about-row"><span className="tx">Version {version}{updateNote && <small>{updateNote}</small>}</span><span className="r">{update?.updateAvailable && update.tag ? <button className="set-text-button" onClick={() => { void codeburn.openExternal(releasePageUrl(update.tag!)) }}>Download</button> : null}</span></div>
+          <div className="about-row"><span className="tx">Version {version}{updateNote && <small>{updateNote}</small>}</span><span className="r">{update?.updateAvailable && update.tag ? <button className="set-text-button" onClick={() => { void codeburn.openExternal(updateDownloadUrl(update.tag!)) }}>Download</button> : null}</span></div>
         </div>
       </div>
     </section>