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/Dockerfile

@@ -1,5 +1,9 @@
 FROM node:22-alpine AS build
 
+# Same value as the backend's BUILD_VERSION so the client can compare them.
+ARG BUILD_VERSION=unknown
+ENV VITE_BUILD_VERSION=${BUILD_VERSION}
+
 WORKDIR /app
 COPY package.json package-lock.json ./
 RUN npm ci --no-audit --no-fund

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)

frontend/vite.config.js

@@ -1,7 +1,22 @@
 import { defineConfig } from 'vite'
 import vue from '@vitejs/plugin-vue'
+import { execSync } from 'node:child_process'
+
+// Short git SHA (or a timestamp fallback) baked into the bundle so the client
+// can detect when the server is running a newer build and reload itself.
+let buildVersion = process.env.VITE_BUILD_VERSION || String(Date.now())
+if (!process.env.VITE_BUILD_VERSION) {
+  try {
+    buildVersion = execSync('git rev-parse --short HEAD').toString().trim()
+  } catch {
+    // not a git checkout; keep the timestamp
+  }
+}
 
 export default defineConfig({
+  define: {
+    __BUILD_VERSION__: JSON.stringify(buildVersion),
+  },
   plugins: [vue()],
   server: {
     port: 5173,