enforce client server compatibility

src/App.svelte

@@ -4,6 +4,7 @@
   let serverAddress = 'http://127.0.0.1:8787';
   let connectionState = 'OFFLINE';
   let serverVersion = '—';
+  let serverCompatibility = '';
   let diagnostics: { status: string; database: string; twitch_identity_count: number; unseen_notification_count: number; realtime: string } | undefined;
   let backups: Array<{ filename: string; size_bytes: number; modified_at: string | null }> = [];
   let backupError = '';
@@ -101,6 +102,24 @@
     bot: { connected: false, missing_scopes: [], reauthorization_required: false },
   };
 
+  const CLIENT_VERSION = '0.1.0';
+
+  function versionParts(value: string) {
+    const match = value.match(/^(\d+)\.(\d+)\.(\d+)/);
+    return match ? [Number(match[1]), Number(match[2]), Number(match[3])] : undefined;
+  }
+
+  function isClientCompatible(minimum: string, maximum: string) {
+    const client = versionParts(CLIENT_VERSION);
+    const minimumParts = versionParts(minimum);
+    const maximumParts = versionParts(maximum);
+    if (!client || !minimumParts) return false;
+    const compare = (left: number[], right: number[]) => left[0] - right[0] || left[1] - right[1] || left[2] - right[2];
+    if (compare(client, minimumParts) < 0) return false;
+    if (maximum === '0.x' || !maximumParts) return true;
+    return compare(client, maximumParts) <= 0;
+  }
+
   $: if (authenticated && selectedOverlayId && overlayName && !overlayBusy) {
     const signature = overlayDraftSignature();
     cacheOverlayDraft();
@@ -129,6 +148,13 @@
         if (!response.ok) throw new Error(`HTTP ${response.status}`);
         const info: { server_version: string; minimum_client_version?: string; maximum_client_version?: string } = await response.json();
         serverVersion = info.server_version;
+        if (info.minimum_client_version && info.maximum_client_version && !isClientCompatible(info.minimum_client_version, info.maximum_client_version)) {
+          serverCompatibility = `Requires client ${info.minimum_client_version}–${info.maximum_client_version}`;
+          connectionState = 'INCOMPATIBLE';
+          connectionNotice = 'Client update required';
+          return;
+        }
+        serverCompatibility = info.minimum_client_version && info.maximum_client_version ? `${info.minimum_client_version}–${info.maximum_client_version}` : '';
         connectionState = 'CONNECTED';
         connectionNotice = '';
         return;
@@ -141,6 +167,10 @@
   }
 
   async function login() {
+    if (connectionState === 'INCOMPATIBLE') {
+      authError = 'This client version is not compatible with the server.';
+      return;
+    }
     authBusy = true;
     authError = '';
     try {