Perf: Serve homepage and assets without invoking Functions

Add _routes.json so /, /robots.txt and /assets/* skip the worker and
don't count against the Functions request quota. rate-limit.js moves to
assets/ so the homepage reads it client-side instead of via HTMLRewriter.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

_routes.json

@@ -0,0 +1,5 @@
+{
+  "version": 1,
+  "include": ["/*"],
+  "exclude": ["/", "/index.html", "/robots.txt", "/assets/*"]
+}

assets/rate-limit.js

@@ -1,5 +1,6 @@
 // New searches (cache misses) allowed per IP per day, reset at 00:00 UTC. Cache hits never count.
-// Safe to edit by hand. The homepage reads these automatically; README.md needs a manual update.
+// Safe to edit by hand. Imported by the worker and by the homepage (as a static file, so no Functions quota);
+// README.md needs a manual update.
 // The burst limit (~10 req/10s) is a Cloudflare WAF rule, not set here.
 export const DAILY_LIMIT = 35;
 export const FREE_DAILY_LIMIT = 100;

functions/[[path]].js

@@ -2,7 +2,7 @@ import { braveImageSearch } from "./_utils/brave.js";
 import { bingImageSearchFallback } from "./_utils/bing.js";
 import { freeImageUrls, parseFreeSource, FREE_UA } from "./_utils/free.js";
 import { isFlickrPlaceholder } from "./_utils/flickr.js";
-import * as LIMITS from "./_utils/rate-limit.js";
+import * as LIMITS from "../assets/rate-limit.js";
 
 const TTL_SECONDS = 90 * 24 * 60 * 60;
 const MAX_INDEX = 20;
@@ -13,8 +13,8 @@ export async function onRequest(context) {
   const path = params.path?.join("/") || "";
   const asset = f => env.ASSETS.fetch(new Request(new URL(`/assets/${f}`, url.origin)));
 
-  if (!path || path === "index.html") return homepage(env, url);
-  if (path === "robots.txt" || path.startsWith("assets/")) {
+  // _routes.json serves these statically without invoking this function; kept as a fallback
+  if (!path || path === "index.html" || path === "robots.txt" || path.startsWith("assets/")) {
     return env.ASSETS.fetch(request);
   }
   if (path === "favicon.ico") return asset("favicon.ico");
@@ -207,20 +207,6 @@ async function* webImageUrls(context, query) {
   yield* (await bingImageSearchFallback(query)) || [];
 }
 
-// Fills each <span data-limit="NAME"> with that export of rate-limit.js, so the page never shows stale limits.
-// Fetched without the browser's If-None-Match and served without an ETag, so a cached copy can't either.
-async function homepage(env, url) {
-  const res = await env.ASSETS.fetch(new Request(url));
-  const headers = new Headers(res.headers);
-  headers.delete("etag");
-  return new HTMLRewriter().on("[data-limit]", {
-    element: e => {
-      const v = LIMITS[e.getAttribute("data-limit")];
-      if (v != null) e.setInnerContent(`${v}`);
-    }
-  }).transform(new Response(res.body, { status: res.status, headers }));
-}
-
 async function setupSurreal(env) {
   if (!env.SURREAL_URL || !env.SURREAL_USER || !env.SURREAL_PASS) return jsonResponse(500, { error: "SurrealDB env vars missing" });
   const sql = `DEFINE NAMESPACE IF NOT EXISTS direct_img;

index.html

@@ -127,5 +127,9 @@ Use images to complement your responses, powered by Brave.</code></pre>
             },()=>getSelection().selectAllChildren(p));
         };
     </script>
+    <script type="module">
+        import * as L from '/assets/rate-limit.js';
+        for(const e of document.querySelectorAll('[data-limit]'))e.textContent=L[e.dataset.limit]??e.textContent;
+    </script>
 </body>
 </html>