fix(cdn): serve pre-compressed R2 bodies with encodeBody manual

Second half of the staging Firefox boot failure: the bucket stores
artifacts brotli-compressed (publish-wasm --compress br) with
Content-Encoding in the object metadata, but the worker returned them
with the default encodeBody:'automatic' — the runtime drops a user-set
Content-Encoding and re-negotiates, and on workers.dev that served the
raw brotli bytes with NO encoding header. The editor <script> tags
loaded binary garbage: Firefox fires onload and silently executes
nothing, so wxElementRegistry/Module never appeared even after the 206
fix. encodeBody:'manual' passes the header+body through untouched
(verified against local workerd with a br-encoded seeded object).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PmR6goSk7JC17h7fkgGvHG

workers/cdn/src/index.ts

@@ -86,9 +86,21 @@ export default {
       headers.set("Content-Length", String(object.size));
     }
 
+    // The bucket stores artifacts PRE-COMPRESSED (publish-wasm --compress br,
+    // Content-Encoding in the object metadata). `encodeBody: "manual"` tells
+    // the runtime the body already matches the Content-Encoding header, so it
+    // passes both through untouched. The default "automatic" mode DROPS a
+    // user-set Content-Encoding and re-negotiates against the client's
+    // Accept-Encoding — behind prod's custom-domain edge that happened to
+    // round-trip, but on workers.dev it served the raw brotli bytes with NO
+    // encoding header: binary garbage where the browser expected JS/wasm.
+    // Firefox executed the garbage <script> to nothing (silently — onload
+    // still fires), leaving the editor glue inert: the second half of the
+    // "runtime did not initialize (no FS)" staging boot failure.
     return new Response(request.method === "HEAD" ? null : object.body, {
       status,
       headers,
+      encodeBody: "manual",
     });
   },
 };