feat(core-shared): add TanStack Start security header adapter

Exports withSecurityHeaders() and getNonce() from the
./security/tanstack subpath. withSecurityHeaders() returns all six
security headers plus x-nonce for use inside a TanStack/Nitro H3
server middleware; getNonce() reads x-nonce from the node request
headers forwarded by that middleware.

Mirrors the ./security/next adapter pattern while staying free of
any @tanstack/start dependency — the adapter works with plain H3
IncomingMessage types that TanStack Start exposes at wiring time
(Story 09).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-shared/package.json

@@ -23,7 +23,8 @@
     "./instrumentation/sentry/init-client": "./src/instrumentation/sentry/init-client.ts",
     "./instrumentation/sentry/init-client-react": "./src/instrumentation/sentry/init-client-react.ts",
     "./security": "./src/security/index.ts",
-    "./security/next": "./src/security/next/index.ts"
+    "./security/next": "./src/security/next/index.ts",
+    "./security/tanstack": "./src/security/tanstack/index.ts"
   },
   "scripts": {
     "build": "tsc --noEmit",

packages/core-shared/src/security/tanstack/get-nonce.test.ts

@@ -0,0 +1,28 @@
+import { describe, it, expect } from "vitest";
+import { getNonce } from "@/security/tanstack/get-nonce";
+
+describe("getNonce", () => {
+  it("reads x-nonce from node request headers", () => {
+    expect(getNonce({ headers: { "x-nonce": "test-nonce-value" } })).toBe(
+      "test-nonce-value",
+    );
+  });
+
+  it("returns the first value when x-nonce is an array", () => {
+    expect(
+      getNonce({ headers: { "x-nonce": ["first-nonce", "second"] } }),
+    ).toBe("first-nonce");
+  });
+
+  it("returns empty string when x-nonce is absent", () => {
+    expect(getNonce({ headers: {} })).toBe("");
+  });
+
+  it("returns empty string when x-nonce is undefined", () => {
+    expect(getNonce({ headers: { "x-nonce": undefined } })).toBe("");
+  });
+
+  it("returns empty string when x-nonce is an empty array", () => {
+    expect(getNonce({ headers: { "x-nonce": [] } })).toBe("");
+  });
+});

packages/core-shared/src/security/tanstack/get-nonce.ts

@@ -0,0 +1,14 @@
+/** Minimal shape of H3's event.node.req used to read x-nonce. */
+interface NodeRequest {
+  headers: Record<string, string | string[] | undefined>;
+}
+
+/**
+ * Reads the nonce from a TanStack Start / H3 server request.
+ * The nonce is set on req.headers["x-nonce"] by withSecurityHeaders().
+ */
+export function getNonce(req: NodeRequest): string {
+  const value = req.headers["x-nonce"];
+  if (Array.isArray(value)) return value[0] ?? "";
+  return value ?? "";
+}

packages/core-shared/src/security/tanstack/index.ts

@@ -0,0 +1,3 @@
+export { withSecurityHeaders } from "./middleware";
+export type { TanstackSecurityHeadersResult } from "./middleware";
+export { getNonce } from "./get-nonce";

packages/core-shared/src/security/tanstack/middleware.test.ts

@@ -0,0 +1,52 @@
+import { describe, it, expect, vi } from "vitest";
+import { withSecurityHeaders } from "@/security/tanstack/middleware";
+
+const ALL_SIX_HEADERS = [
+  "Strict-Transport-Security",
+  "X-Frame-Options",
+  "X-Content-Type-Options",
+  "Referrer-Policy",
+  "Permissions-Policy",
+  "Content-Security-Policy",
+] as const;
+
+describe("withSecurityHeaders", () => {
+  it("returns all six security headers", () => {
+    const { headers } = withSecurityHeaders();
+
+    for (const header of ALL_SIX_HEADERS) {
+      expect(headers).toHaveProperty(header);
+    }
+  });
+
+  it("returns x-nonce in headers equal to the returned nonce", () => {
+    const { headers, nonce } = withSecurityHeaders();
+
+    expect(headers["x-nonce"]).toBe(nonce);
+    expect(typeof nonce).toBe("string");
+    expect(nonce.length).toBeGreaterThan(0);
+  });
+
+  it("nonce in x-nonce matches nonce threaded into CSP in production mode", () => {
+    vi.stubEnv("NODE_ENV", "production");
+
+    const { headers, nonce } = withSecurityHeaders();
+
+    expect(headers["Content-Security-Policy"]).toContain(`'nonce-${nonce}'`);
+  });
+
+  it("uses dev-mode CSP when NODE_ENV is not production", () => {
+    vi.stubEnv("NODE_ENV", "test");
+
+    const { headers } = withSecurityHeaders();
+
+    expect(headers["Content-Security-Policy"]).toContain("'unsafe-inline'");
+  });
+
+  it("each call produces a unique nonce", () => {
+    const a = withSecurityHeaders();
+    const b = withSecurityHeaders();
+
+    expect(a.nonce).not.toBe(b.nonce);
+  });
+});

packages/core-shared/src/security/tanstack/middleware.ts

@@ -0,0 +1,24 @@
+import { generateNonce } from "../nonce";
+import { buildSecurityHeaders } from "../build-security-headers";
+
+export type TanstackSecurityHeadersResult = {
+  nonce: string;
+  headers: Record<string, string>;
+};
+
+/**
+ * Generates a nonce and builds all six security headers plus x-nonce.
+ * Intended for use inside a TanStack Start / Nitro server middleware:
+ *   const { nonce, headers } = withSecurityHeaders();
+ *   for (const [k, v] of Object.entries(headers)) setResponseHeader(event, k, v);
+ *   event.node.req.headers["x-nonce"] = nonce; // forward for getNonce()
+ */
+export function withSecurityHeaders(): TanstackSecurityHeadersResult {
+  const nonce = generateNonce();
+  const mode = process.env.NODE_ENV === "production" ? "prod" : "dev";
+  const secHeaders = buildSecurityHeaders({ mode, nonce });
+  return {
+    nonce,
+    headers: { ...secHeaders, "x-nonce": nonce },
+  };
+}