Self-heal a stale cached bundle via a build version

Phones kept running old JS because their cached index.html pointed at an old
hashed asset. Both images now bake the commit SHA as BUILD_VERSION; the backend
exposes it at GET /api/version and the client reloads once with a cache-busting
query when its own baked version differs. Guarded by sessionStorage so it cannot
loop. /api/version is unauthenticated like /api/health.

frontend/src/App.vue

@@ -133,7 +133,27 @@ function handleMessage(message) {
   }
 }
 
+// If the server is running a newer build than this (possibly cached) bundle,
+// reload once with a cache-busting query so phones pick up deploys without a
+// manual hard-refresh. Guarded so it can never loop.
+async function ensureFreshBuild() {
+  try {
+    const { version } = await api.getVersion()
+    if (!version || version === 'unknown') return
+    if (version === __BUILD_VERSION__) return
+    const key = `reloaded:${version}`
+    if (sessionStorage.getItem(key)) return
+    sessionStorage.setItem(key, '1')
+    const url = new URL(window.location.href)
+    url.searchParams.set('v', version)
+    window.location.replace(url.toString())
+  } catch {
+    // ignore; not worth blocking the app
+  }
+}
+
 onMounted(async () => {
+  ensureFreshBuild()
   await Promise.all([
     loadStrategies(),
     loadPresets(),

frontend/src/api.js

@@ -2,6 +2,7 @@ import axios from 'axios'
 
 const http = axios.create({ baseURL: '/api', timeout: 10000 })
 
+export const getVersion = () => http.get('/version').then((r) => r.data)
 export const getStatus = () => http.get('/status').then((r) => r.data)
 export const getStrategies = () => http.get('/strategies').then((r) => r.data)
 export const getPositions = () => http.get('/positions').then((r) => r.data)