fix(dev): proxy content assets to cli server

The CLI content server serves the content directory at the URL root, so
images and other content assets are requested as root-relative paths
(e.g. /adventures/map.png). The dev proxy only forwarded /content, so
those requests fell through to historyApiFallback and the browser got
index.html instead of the asset.

Forward any request that maps to a real file under content/ to the CLI
server, keeping /static/ bundles on the web dev server.

rsbuild.config.ts

@@ -3,6 +3,43 @@ import { pluginBabel } from "@rsbuild/plugin-babel";
 import { pluginSolid } from "@rsbuild/plugin-solid";
 import tailwindcss from "@tailwindcss/postcss";
 import { BundleAnalyzerPlugin } from "webpack-bundle-analyzer";
+import { statSync } from "node:fs";
+import { join, resolve } from "node:path";
+
+// The CLI content server (`npm run dev:cli`, i.e. `tttk serve ./content`) keeps
+// port 3000. It serves the content directory at the URL *root*, so content
+// assets are requested as root-relative paths (e.g. `/adventures/map.png`),
+// not under `/content`.
+const CLI_TARGET = "http://localhost:3000";
+const CONTENT_DIR = resolve(process.cwd(), "content");
+
+/**
+ * True when a request targets a real file inside the content directory.
+ *
+ * Mirrors the CLI server's static handling: only files are served, so a
+ * directory path falls through to the SPA fallback. Requests for content
+ * assets must be proxied to the CLI; otherwise they reach
+ * `historyApiFallback` and the browser receives `index.html` instead of the
+ * asset (which is why images failed to render in dev).
+ */
+function isContentFile(pathname: string): boolean {
+  // The web dev server owns its own bundled assets under /static/.
+  if (pathname.startsWith("/static/")) return false;
+
+  let relativePath: string;
+  try {
+    relativePath = decodeURIComponent(pathname).replace(/^\/+/, "");
+  } catch {
+    return false;
+  }
+  if (!relativePath) return false;
+
+  try {
+    return statSync(join(CONTENT_DIR, relativePath)).isFile();
+  } catch {
+    return false;
+  }
+}
 
 export default defineConfig({
   plugins: [
@@ -51,14 +88,25 @@ export default defineConfig({
     // Dev web server runs on its own port; the CLI content server keeps
     // port 3000 (see the proxy targets below).
     port: 5173,
-    proxy: {
-      // Proxy content API requests to the CLI dev server (npm run tttk)
-      "/__CONTENT_INDEX.json": "http://localhost:3000",
-      "/__COMPLETIONS.json": "http://localhost:3000",
-      "/__CONTENT_REGISTRY.json": "http://localhost:3000",
-      "/content": "http://localhost:3000",
-      "/.ttrpg": "http://localhost:3000",
-    },
+    proxy: [
+      {
+        // Content API requests served by the CLI dev server (npm run dev:cli).
+        context: [
+          "/__CONTENT_INDEX.json",
+          "/__COMPLETIONS.json",
+          "/__CONTENT_REGISTRY.json",
+          "/.ttrpg",
+        ],
+        target: CLI_TARGET,
+      },
+      {
+        // Content assets (images, css, csv, …) live at the URL root on the CLI
+        // server, so forward any request that maps to a real file under
+        // content/ instead of letting it hit the SPA fallback.
+        context: (pathname: string) => isContentFile(pathname),
+        target: CLI_TARGET,
+      },
+    ],
     historyApiFallback: true,
   },
   output: {