Warm the server cache from client-side navigations, PUBLIC_SSR_WARM opts out

src/lib/config.ts

@@ -21,6 +21,11 @@ if (MODE === "simple" && !GROUP_ID) {
 // Server-side rendering: opt-in, decided at build time (vite.config.ts bakes
 // PUBLIC_SSR in; svelte.config.js picks the matching adapter).
 export const SSR_ENABLED = __SQUALK_SSR__;
+// With SSR on, a client-side navigation also asks the server for the same
+// snapshot (without waiting for it) so the page is already cached for the
+// next refresh, shared link or crawler. Costs one server→relay query per
+// navigation; opt out with PUBLIC_SSR_WARM=no.
+export const SSR_WARM = SSR_ENABLED && env.PUBLIC_SSR_WARM !== "no";
 // Server-rendered pages and snapshots are anonymous, so a shared cache may
 // hold them: fresh for 5 minutes, served stale for an hour while revalidating.
 // Browsers always revalidate (max-age=0) so a login shows its content at once.

src/lib/forum/snapshot.ts

@@ -1,5 +1,6 @@
 import { browser } from "$app/environment";
 import { error } from "@sveltejs/kit";
+import { SSR_WARM } from "$lib/config";
 import type { NostrUser } from "$lib/gadgets";
 import type { GroupMetadata, GroupSummary } from "./groups";
 import type { Resource } from "./resources";
@@ -37,14 +38,18 @@ type Fetch = typeof fetch;
 // Read a snapshot endpoint. On the server the response is inlined into the
 // HTML; in the browser it is consumed only while hydrating that HTML. Client
 // navigations get null, leaving the stores to fetch live (and authenticated)
-// data as they always did — the same path a client-only build takes.
+// data as they always did — the same path a client-only build takes — but
+// may still poke the endpoint so the server has the page cached.
 // A 404 from the endpoint becomes a real 404 page on the server, so crawlers
 // never index an empty shell; the client keeps its own not-found handling.
 export async function snapshot<T>(
   fetch: Fetch,
   url: string,
 ): Promise<T | null> {
-  if (browser && !hasInlinedResponse(url)) return null;
+  if (browser && !hasInlinedResponse(url)) {
+    if (SSR_WARM) fetch(url).catch(() => {});
+    return null;
+  }
   let res: Response;
   try {
     res = await fetch(url);