feat: add deployment reload controls

lib/realtime/sse.ts

@@ -19,8 +19,16 @@ type SubscriptionOptions = {
   onopen?: (event: Event) => void;
 };
 
-type StreamOptions = {
+type StreamMessage<T extends EventMap> = {
+  [K in Extract<keyof T, string>]: {
+    event: K;
+    data: z.input<T[K]>;
+  };
+}[Extract<keyof T, string>];
+
+type StreamOptions<T extends EventMap> = {
   signal?: AbortSignal;
+  motd?: StreamMessage<T> | StreamMessage<T>[];
 };
 
 const redisEnvelopeSchema = z.object({
@@ -154,7 +162,11 @@ export class SseEndpoint<T extends EventMap> {
     }
   }
 
-  async stream({ signal }: StreamOptions = {}) {
+  async stream({ signal, motd }: StreamOptions<T> = {}) {
+    const initialMessages = (Array.isArray(motd) ? motd : motd ? [motd] : [])
+      .map(({ event, data }) =>
+        encodeEvent(event, this.events[event].parse(data)),
+      );
     const subscriber = await getRedisSubscriber();
     const topic = this.topic;
     const channel = channelName(this.topic);
@@ -223,6 +235,7 @@ export class SseEndpoint<T extends EventMap> {
       start(streamController) {
         controller = streamController;
         write(`retry: ${DEFAULT_RETRY_MS}\n\n: connected ${topic}\n\n`);
+        for (const message of initialMessages) write(message);
 
         receive = handleMessage;
         for (const message of pendingMessages.splice(0)) {
@@ -287,6 +300,12 @@ export function createSseEndpoints<
 const updateActionSchema = z.enum(["created", "updated", "deleted"]);
 
 export const sse = createSseEndpoints({
+  active: {
+    events: {
+      version: z.string().min(1),
+      refresh: z.string().min(1).nullable(),
+    },
+  },
   forms: {
     events: {
       update: z.object({