Security hardening from 2026-07-01 audit

- Exclude supabase/ from Docker build context (leaked service_role key file)
- /api/files: exact per-user namespace match + reject path traversal;
  storage resolveKey rejects ".."/"." segments (fixes cross-user file read)
- Add ownsProperty/Unit/Tenant checks to tenants, maintenance (landlord path),
  and documents (JSON branch, now field-whitelisted) create handlers
- Escape user data in follow-up + payment-link emails (reuse escapeHtml)
- Neutralize CSV formula injection in toCsv + export routes
- Tighter sign-in rate limit (10/min); env-gated email verification + sender
- Per-request nonce CSP; drop script-src 'unsafe-inline' (styles unchanged)
- Add input length bounds; validate follow-ups POST body

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

proxy.ts

@@ -27,6 +27,27 @@ const PROTECTED_PATHS = [
 
 const AUTH_PATHS = ["/login", "/signup", "/forgot-password"]
 
+// Build the per-request Content-Security-Policy. `script-src` carries a
+// per-request nonce instead of 'unsafe-inline'. `style-src` keeps
+// 'unsafe-inline' because Radix / Tailwind / framer-motion inject inline
+// styles and removing it would break the UI. Next.js reads the nonce from the
+// `content-security-policy` request header and applies it to its own inline
+// scripts automatically.
+function buildCsp(nonce: string): string {
+  return [
+    "default-src 'self'",
+    "img-src 'self' data: blob: https:",
+    "style-src 'self' 'unsafe-inline'",
+    `script-src 'self' 'nonce-${nonce}' https://challenges.cloudflare.com`,
+    "font-src 'self' data:",
+    "connect-src 'self' https://api.stripe.com https://api.openai.com https://api.resend.com https://challenges.cloudflare.com",
+    "frame-src https://js.stripe.com https://hooks.stripe.com https://challenges.cloudflare.com",
+    "frame-ancestors 'none'",
+    "base-uri 'self'",
+    "form-action 'self'",
+  ].join("; ")
+}
+
 export async function proxy(request: NextRequest) {
   const pathname = request.nextUrl.pathname
 
@@ -48,7 +69,21 @@ export async function proxy(request: NextRequest) {
     return NextResponse.redirect(url)
   }
 
-  return NextResponse.next()
+  // Per-request CSP nonce. UUID contains only hex + dashes, so it never
+  // includes HTML-escape characters (which Next rejects in nonces).
+  const nonce = crypto.randomUUID()
+  const csp = buildCsp(nonce)
+
+  // Forward the nonce + CSP on the request headers so Next.js can pick up the
+  // nonce and apply it to its own inline scripts during render.
+  const requestHeaders = new Headers(request.headers)
+  requestHeaders.set("x-nonce", nonce)
+  requestHeaders.set("Content-Security-Policy", csp)
+
+  const response = NextResponse.next({ request: { headers: requestHeaders } })
+  // Also set the CSP on the outgoing response so the browser enforces it.
+  response.headers.set("Content-Security-Policy", csp)
+  return response
 }
 
 export const config = {