diff --git a/packages/studio/package-subpaths.json b/packages/studio/package-subpaths.json
index 4bbea0a261..ac6ec74faf 100644
--- a/packages/studio/package-subpaths.json
+++ b/packages/studio/package-subpaths.json
@@ -19,6 +19,12 @@
       "types": null,
       "environments": ["browser"]
     },
+    "./styles.css": {
+      "source": "./src/styles/studio.css",
+      "runtime": "./dist/styles.css",
+      "types": null,
+      "environments": ["browser"]
+    },
     "./package.json": {
       "source": "./package.json",
       "runtime": "./package.json",
diff --git a/packages/studio/package.json b/packages/studio/package.json
index 744ee96b6a..79a4d578e2 100644
--- a/packages/studio/package.json
+++ b/packages/studio/package.json
@@ -27,6 +27,7 @@
       "types": "./src/styles/tailwind-preset.ts"
     },
     "./theme.css": "./src/styles/theme.css",
+    "./styles.css": "./src/styles/studio.css",
     "./package.json": "./package.json"
   },
   "publishConfig": {
@@ -41,6 +42,7 @@
         "types": "./dist/styles/tailwind-preset.d.ts"
       },
       "./theme.css": "./src/styles/theme.css",
+      "./styles.css": "./dist/styles.css",
       "./package.json": "./package.json"
     },
     "main": "./dist/index.js",
diff --git a/packages/studio/src/components/StudioHeader.tsx b/packages/studio/src/components/StudioHeader.tsx
index 7b88371373..10b733c830 100644
--- a/packages/studio/src/components/StudioHeader.tsx
+++ b/packages/studio/src/components/StudioHeader.tsx
@@ -17,7 +17,7 @@ export interface StudioHeaderProps {
   onExport?: () => void;
 }
 
-function HyperframesLogo() {
+export function HyperframesLogo() {
   // Full logo from logo-dark.svg (263×79): heygen label + gradient mark + hyperframes wordmark.
   // All fill="black" paths inverted to white for the dark header.
   const height = 28;
diff --git a/packages/studio/src/headerExports.test.tsx b/packages/studio/src/headerExports.test.tsx
new file mode 100644
index 0000000000..348fafef44
--- /dev/null
+++ b/packages/studio/src/headerExports.test.tsx
@@ -0,0 +1,23 @@
+// @vitest-environment happy-dom
+// Imports the header logo and button size classes the way a host app does: by package name.
+import { createRoot } from "react-dom/client";
+import { act } from "react";
+import { describe, expect, it } from "vitest";
+import { HyperframesLogo, buttonSizes } from "@hyperframes/studio";
+
+Object.assign(globalThis, { IS_REACT_ACT_ENVIRONMENT: true });
+
+describe("header package exports", () => {
+  it("mounts the logo mark", async () => {
+    const el = document.createElement("div");
+    document.body.append(el);
+    const root = createRoot(el);
+    await act(async () => root.render(<HyperframesLogo />));
+    expect(el.querySelector("svg")).not.toBeNull();
+    await act(async () => root.unmount());
+  });
+
+  it("exposes the button size classes a host reuses for matching chrome", () => {
+    expect(buttonSizes.md).toEqual(expect.any(String));
+  });
+});
diff --git a/packages/studio/src/index.ts b/packages/studio/src/index.ts
index 9608bc6ca8..9eb5473131 100644
--- a/packages/studio/src/index.ts
+++ b/packages/studio/src/index.ts
@@ -1,9 +1,10 @@
 // UI primitives
-export { Button, buttonBase, buttonVariants } from "./components/ui/Button";
+export { Button, buttonBase, buttonSizes, buttonVariants } from "./components/ui/Button";
 export type { ButtonSize, ButtonVariant, PreviewState } from "./components/ui/Button";
 export { IconButton } from "./components/ui/IconButton";
 export { Tab, TabPanel, Tabs, TabsList } from "./components/ui/Tabs";
 export { Tooltip } from "./components/ui/Tooltip";
+export { HyperframesLogo } from "./components/StudioHeader";
 export { cn } from "./components/ui/cn";
 export {
   ContextMenu,
diff --git a/packages/studio/vite.config.test.ts b/packages/studio/vite.config.test.ts
new file mode 100644
index 0000000000..29f35e916e
--- /dev/null
+++ b/packages/studio/vite.config.test.ts
@@ -0,0 +1,89 @@
+import { mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join, resolve } from "node:path";
+import { describe, expect, it } from "vitest";
+import config, { stableStylesCssPlugin } from "./vite.config";
+
+const packageJson = JSON.parse(readFileSync(resolve(__dirname, "package.json"), "utf8")) as {
+  publishConfig: { exports: Record<string, string> };
+};
+const subpaths = JSON.parse(readFileSync(resolve(__dirname, "package-subpaths.json"), "utf8")) as {
+  subpaths: Record<string, { runtime: string }>;
+};
+
+// Rollup's own asset/chunk types aren't imported here; the plugin only reads
+// `type` and `fileName`, so a minimal shape is enough to drive it.
+function asset(fileName: string): { type: "asset"; fileName: string } {
+  return { type: "asset", fileName };
+}
+function chunk(fileName: string): { type: "chunk"; fileName: string } {
+  return { type: "chunk", fileName };
+}
+
+function callWriteBundle(dir: string, bundle: Record<string, unknown>): void {
+  const writeBundle = stableStylesCssPlugin().writeBundle as (
+    options: { dir: string },
+    bundle: Record<string, unknown>,
+  ) => void;
+  writeBundle({ dir }, bundle);
+}
+
+describe("build.rollupOptions", () => {
+  it("does not override assetFileNames, so every asset stays content-hashed", () => {
+    // Regression for the cache bug this PR fixed: /assets/* is served with a
+    // one-year immutable Cache-Control by filename convention alone
+    // (packages/cli/src/server/studioServer.ts), so an unhashed name there
+    // sticks to every CLI user's cache for a year.
+    expect(config.build?.rollupOptions?.output).toBeUndefined();
+  });
+});
+
+describe("./styles.css export path", () => {
+  it("resolves outside dist/assets, so it never inherits the immutable cache header", () => {
+    const publishedPath = packageJson.publishConfig.exports["./styles.css"];
+    const runtimePath = subpaths.subpaths["./styles.css"]?.runtime;
+    expect(publishedPath).toBe("./dist/styles.css");
+    expect(runtimePath).toBe("./dist/styles.css");
+    for (const path of [publishedPath, runtimePath]) {
+      expect(path?.startsWith("./dist/assets/")).toBe(false);
+    }
+  });
+});
+
+describe("stableStylesCssPlugin", () => {
+  function tmpDir(): string {
+    return mkdtempSync(join(tmpdir(), "styles-css-plugin-"));
+  }
+
+  it("copies the single CSS asset, unhashed, to dist root, ignoring non-asset bundle entries", () => {
+    const dir = tmpDir();
+    try {
+      writeFileSync(join(dir, "app-abc123.css"), "body{color:red}");
+      callWriteBundle(dir, {
+        "app-abc123.css": asset("app-abc123.css"),
+        "app-def456.js": chunk("app-def456.js"),
+        // A chunk can't really carry a `.css` name, but proving the `type`
+        // guard (not just the filename suffix) does the filtering keeps the
+        // count right if a future asset kind ever ends in `.css` too.
+        "fake.css": chunk("fake.css"),
+      });
+      expect(readFileSync(join(dir, "styles.css"), "utf8")).toBe("body{color:red}");
+    } finally {
+      rmSync(dir, { recursive: true, force: true });
+    }
+  });
+
+  it("throws instead of guessing when the build emits zero or several CSS assets", () => {
+    const dir = tmpDir();
+    try {
+      expect(() => callWriteBundle(dir, { "app.js": chunk("app.js") })).toThrow(/found 0/);
+      writeFileSync(join(dir, "a.css"), "a");
+      writeFileSync(join(dir, "b.css"), "b");
+      expect(() =>
+        callWriteBundle(dir, { "a.css": asset("a.css"), "b.css": asset("b.css") }),
+      ).toThrow(/found 2/);
+    } finally {
+      rmSync(dir, { recursive: true, force: true });
+    }
+  });
+});
diff --git a/packages/studio/vite.config.ts b/packages/studio/vite.config.ts
index 2c4dd85e18..af78da1b4c 100644
--- a/packages/studio/vite.config.ts
+++ b/packages/studio/vite.config.ts
@@ -1,7 +1,14 @@
 import { defineConfig, type Plugin } from "vite";
 import react from "@vitejs/plugin-react";
 import tailwindcss from "@tailwindcss/vite";
-import { readFileSync, readdirSync, existsSync, lstatSync, realpathSync } from "node:fs";
+import {
+  copyFileSync,
+  readFileSync,
+  readdirSync,
+  existsSync,
+  lstatSync,
+  realpathSync,
+} from "node:fs";
 import { join, resolve } from "node:path";
 import { readNodeRequestBody } from "./vite.request-body.js";
 import { watch } from "chokidar";
@@ -27,6 +34,30 @@ async function loadRuntimeSourceForDev(
 
 const studioPkg = JSON.parse(readFileSync(resolve(__dirname, "package.json"), "utf-8"));
 
+/**
+ * Copies the build's one CSS asset, unhashed, to `dist/styles.css` for the
+ * `./styles.css` export. Throws if the build ever emits more than one.
+ */
+export function stableStylesCssPlugin(): Plugin {
+  return {
+    name: "studio-stable-styles-css",
+    writeBundle(options, bundle) {
+      const cssAssets = Object.values(bundle).filter(
+        (item) => item.type === "asset" && item.fileName.endsWith(".css"),
+      );
+      if (cssAssets.length !== 1) {
+        throw new Error(
+          `stableStylesCssPlugin: expected exactly one CSS asset for the ./styles.css ` +
+            `export, found ${cssAssets.length} (${cssAssets.map((a) => a.fileName).join(", ") || "none"}). ` +
+            `Scope this plugin to the entry stylesheet instead of assuming a single emit.`,
+        );
+      }
+      const outDir = options.dir ?? "dist";
+      copyFileSync(join(outDir, cssAssets[0]!.fileName), join(outDir, "styles.css"));
+    },
+  };
+}
+
 // ── Bridge Hono fetch → Node http response ───────────────────────────────────
 
 async function bridgeHonoResponse(
@@ -262,6 +293,12 @@ export default defineConfig({
   build: {
     outDir: "dist",
     emptyOutDir: true,
+    rollupOptions: {
+      // /assets/* caches by filename alone, immutably, for a year
+      // (studioServer.ts). Keep every hash; copy one CSS file, unhashed,
+      // to the dist ROOT instead for the ./styles.css export.
+      plugins: [stableStylesCssPlugin()],
+    },
   },
   optimizeDeps: {
     include: ["bpm-detective"],