✨ feat: implement build version check and update build info handling

frontend/src/lib/versionCheck.ts

@@ -0,0 +1,54 @@
+/**
+ * Build-Version-Check: Auto-Reload when a newer build is detected on the server
+ *
+ * Every GET API response includes the header X-Build-Time with the server's build
+ * timestamp. If it's newer than the one embedded in the frontend bundle, a toast
+ * is shown and the page is automatically reloaded after a short delay.
+ */
+import { buildTime } from "./buildInfo"
+import { addToast } from "./toast"
+
+/** Prevents multiple triggers within the same page session */
+let triggered = false
+
+const RELOAD_DELAY_MS = 3000
+const STORAGE_KEY = "__build_reload__"
+
+/**
+ * Checks whether the server has a newer build than the current frontend bundle.
+ * Only runs in the browser (SSR-safe).
+ *
+ * @param serverBuildTime - ISO timestamp from the X-Build-Time response header
+ */
+export function checkBuildVersion(serverBuildTime: string | null | undefined): void {
+    if (!serverBuildTime || typeof window === "undefined") return
+    if (triggered) return
+
+    // Only react if the server build is actually newer
+    if (serverBuildTime <= buildTime) return
+
+    // Loop protection: if we already reloaded for this exact build, don't reload again
+    // (e.g. CDN/cache still serving old bundle)
+    try {
+        if (sessionStorage.getItem(STORAGE_KEY) === serverBuildTime) return
+    } catch (_) {
+        // sessionStorage not available (e.g. privacy mode) – continue anyway
+    }
+
+    triggered = true
+
+    // Show toast notification
+    addToast("New version available – page will refresh…", "info", RELOAD_DELAY_MS + 2000)
+
+    // Remember that we're reloading for this build timestamp
+    try {
+        sessionStorage.setItem(STORAGE_KEY, serverBuildTime)
+    } catch (_) {
+        // ignore
+    }
+
+    // Auto-reload after short delay so toast is visible
+    setTimeout(() => {
+        window.location.reload()
+    }, RELOAD_DELAY_MS)
+}