A page from before a deploy can still find its chunks, or reload once

Sentry WIZWAR-5: a table open through a deploy asked for the replay
module by its old hashed name, the deploy had deleted it, and the
server answered with the app shell as text/html — "not a valid
JavaScript MIME type". Three guards: deploys keep old chunks for a
week instead of deleting them; a missing asset is a plain 404, never
the shell; and the client reloads once when Vite reports a failed
import, so the live bundle takes over.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jm2auWk6RP71CjaAb4FMoG

packages/server/src/index.ts

@@ -387,7 +387,14 @@ const httpServer = createServer((req, res) => {
       res.writeHead(403).end();
       return;
     }
-    if (!existsSync(file)) file = join(staticRoot, "index.html"); // SPA fallback
+    if (!existsSync(file)) {
+      // A hashed asset that is gone is gone: a page built before the last
+      // deploy asking for its old chunk gets a plain 404 it can act on,
+      // never the app shell as text/html. Every other unknown path is the
+      // app's to route.
+      if (url.startsWith("/assets/")) { res.writeHead(404, { "content-type": "text/plain" }).end("gone"); return; }
+      file = join(staticRoot, "index.html");
+    }
     // Resolve symlinks and re-verify the real location stays inside the root.
     const real = realpathSync(file);
     if (real !== staticRoot && !real.startsWith(staticRoot + sep)) {