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>

app/api/documents/route.ts

@@ -4,6 +4,7 @@ import { db } from "@/lib/db"
 import { documents, properties } from "@/lib/db/schema"
 import { getSessionUser } from "@/lib/session"
 import { saveFile } from "@/lib/storage"
+import { ownsProperty, ownsTenant } from "@/lib/db/ownership"
 
 export async function GET(request: Request) {
   const user = await getSessionUser()
@@ -76,9 +77,31 @@ export async function POST(request: Request) {
 
   // JSON fallback (metadata only)
   const body = (await request.json()) as Record<string, unknown>
+  const propertyId = body.property_id as string | undefined
+  const tenantId = body.tenant_id as string | undefined
+
+  // Verify the property/tenant belong to the user before attaching a document.
+  if (!(await ownsProperty(user.id, propertyId))) {
+    return NextResponse.json({ error: "Property not found" }, { status: 404 })
+  }
+  if (!(await ownsTenant(user.id, tenantId))) {
+    return NextResponse.json({ error: "Tenant not found" }, { status: 404 })
+  }
+
+  // Whitelist insertable columns — never trust client-supplied user_id/id/created_at.
   const [data] = await db
     .insert(documents)
-    .values({ ...(body as typeof documents.$inferInsert), user_id: user.id })
+    .values({
+      user_id: user.id,
+      property_id: propertyId as string,
+      tenant_id: tenantId,
+      name: body.name as string,
+      category: (body.category as typeof documents.$inferInsert.category) ?? "other",
+      file_url: body.file_url as string,
+      storage_path: body.storage_path as string | undefined,
+      file_type: body.file_type as string | undefined,
+      file_size: body.file_size as number | undefined,
+    })
     .returning()
 
   return NextResponse.json(data, { status: 201 })