diff --git a/docs/craftvia/ARCHITEKTUR.md b/docs/craftvia/ARCHITEKTUR.md
index 1cde6df..6ef129d 100644
--- a/docs/craftvia/ARCHITEKTUR.md
+++ b/docs/craftvia/ARCHITEKTUR.md
@@ -101,6 +101,13 @@ Konfiguration per Env (`AI_EXTRACTION_PROVIDER=anthropic`, `ANTHROPIC_API_KEY`,
 ### 4.7 Berichtsinhalt
 `src/lib/reports/content.ts#ReportContent` (Zod): Snapshot aller Berichtsdaten (Spec §16.2/§17.2) – wird beim Erstellen/Freigeben aus DB gebaut (`services/reports/build-content.ts`) und ist nach `approved` unveränderlich. Änderungen nach Freigabe = neue Version (`lineageId`, `version+1`, alte → `superseded`).
 
+### 4.8 Transaktionen, Header, Uploads (Fundament-Nachträge)
+- **Mehrschritt-Schreibvorgänge nur über `inTransaction(ctx, fn)`** (`src/server/services/context.ts`, basiert auf `tenantTransaction` in `db.ts`). Direktes `ctx.db.$transaction(...)` ist bei `RLS_ENFORCED=true` nicht atomar.
+- Datei-Routen, die im eigenen iframe angezeigt werden dürfen, stehen in `EMBEDDABLE_FILE_ROUTES` (`next.config.ts`, `frame-ancestors 'self'` / `SAMEORIGIN`); alles andere bleibt `DENY`.
+- Request-Bodies über den Proxy: `experimental.proxyClientMaxBodySize = 26mb` (größter Upload 25 MB).
+- Berichtsversionen (§4.7): Eine freigegebene Version wird erst `superseded`, wenn die NEUE Version freigegeben wird – so existiert immer ein gültiges freigegebenes PDF.
+- Neue Personenreferenz-Felder (`…ById`, `userId`) in `src/server/dsgvo/pii-fields.ts` eintragen.
+
 ## 5. Routen
 
 | Bereich | Route | Modul |
diff --git a/next.config.ts b/next.config.ts
index 5be4174..ab580d4 100644
--- a/next.config.ts
+++ b/next.config.ts
@@ -31,6 +31,13 @@ const csp = [
   "object-src 'none'",
 ].join("; ");
 
+// Same-origin embedding for inline document previews (PDF viewer in the import review
+// mask, document previews). Everything else stays frame-ancestors 'none' / DENY.
+const cspEmbeddable = csp.replace("frame-ancestors 'none'", "frame-ancestors 'self'");
+
+// Routes that stream stored files and may be shown in a same-origin <iframe>.
+const EMBEDDABLE_FILE_ROUTES = ["/files/:path*", "/imports/:id/file"];
+
 const securityHeaders = [
   { key: "Content-Security-Policy", value: csp },
   // HSTS bewusst zusätzlich in der App (neben dem Coolify-/Traefik-Proxy).
@@ -46,17 +53,27 @@ const securityHeaders = [
 const nextConfig: NextConfig = {
   // Standalone-Output für den Docker-Multi-Stage-Build (siehe Dockerfile)
   output: "standalone",
+  experimental: {
+    // Proxy (src/proxy.ts) buffers request bodies; the 10 MB default truncates uploads silently.
+    // Largest allowed upload is 25 MB (PDF import) plus multipart overhead.
+    proxyClientMaxBodySize: "26mb",
+  },
   // i18n-Kataloge werden zur Laufzeit per fs geladen (src/i18n/request.ts) — für den
   // standalone-Output explizit mitkopieren.
   outputFileTracingIncludes: {
     "/*": ["./messages/**/*.json"],
   },
   async headers() {
+    // Later entries override same-named headers of earlier matches (Next.js header semantics).
     return [
-      {
-        source: "/:path*",
-        headers: securityHeaders,
-      },
+      { source: "/:path*", headers: securityHeaders },
+      ...EMBEDDABLE_FILE_ROUTES.map((source) => ({
+        source,
+        headers: [
+          { key: "Content-Security-Policy", value: cspEmbeddable },
+          { key: "X-Frame-Options", value: "SAMEORIGIN" },
+        ],
+      })),
     ];
   },
 };
diff --git a/scripts/test-rls-enforcement.ts b/scripts/test-rls-enforcement.ts
index 653307e..686e171 100644
--- a/scripts/test-rls-enforcement.ts
+++ b/scripts/test-rls-enforcement.ts
@@ -42,9 +42,17 @@ async function expectThrow(fn: () => Promise<unknown>, msg: string) {
   }
 }
 
-const RLS_URL =
-  process.env.RLS_DATABASE_URL ??
-  "postgresql://craftvia_app:craftvia_app_local@localhost:5432/craftvia?schema=public";
+/**
+ * Default: same host/port/database as DATABASE_URL, but as the restricted role craftvia_app.
+ * Keeps the test pointed at the database that was actually migrated/seeded (e.g. lane DBs).
+ */
+function defaultRlsUrl(): string {
+  const base = new URL(process.env.DATABASE_URL ?? "postgresql://localhost:5432/craftvia?schema=public");
+  base.username = "craftvia_app";
+  base.password = "craftvia_app_local";
+  return base.toString();
+}
+const RLS_URL = process.env.RLS_DATABASE_URL ?? defaultRlsUrl();
 
 const SLUG_A = "zz-rls-test-a";
 const SLUG_B = "zz-rls-test-b";
diff --git a/scripts/test-tenant-transaction.ts b/scripts/test-tenant-transaction.ts
new file mode 100644
index 0000000..acc9e32
--- /dev/null
+++ b/scripts/test-tenant-transaction.ts
@@ -0,0 +1,102 @@
+import "dotenv/config";
+
+/**
+ * tenantTransaction(): atomic multi-step writes for one tenant.
+ * Runs in the mode given by RLS_ENFORCED (owner path by default). The runner executes this
+ * script once as-is; to verify the RLS path run: RLS_ENFORCED=true npx tsx scripts/test-tenant-transaction.ts
+ * (requires craftvia_app LOGIN, see test-rls-enforcement.ts — otherwise that mode is skipped).
+ *  (1) commit: two writes inside → both visible afterwards
+ *  (2) rollback: two writes, then throw → nothing visible
+ *  (3) a write for another tenant inside the transaction → rejected, whole tx rolled back
+ *  (4) nested tenantTransaction joins the outer transaction (rollback covers both)
+ */
+
+let failures = 0;
+function check(name: string, cond: boolean, detail?: unknown) {
+  if (cond) console.log(`  ✓ ${name}`);
+  else {
+    failures++;
+    console.log(`  ✗ ${name}`, detail ?? "");
+  }
+}
+
+async function main() {
+  const { prisma, dbForTenant, tenantTransaction, RLS_ENFORCED } = await import("../src/server/db");
+  console.log(`Modus: ${RLS_ENFORCED ? "RLS (craftvia_app)" : "Owner"}`);
+
+  const stamp = Date.now();
+  const a = await prisma.tenant.create({ data: { name: "ZZ Tx A", slug: `zz-tx-a-${stamp}` } });
+  const b = await prisma.tenant.create({ data: { name: "ZZ Tx B", slug: `zz-tx-b-${stamp}` } });
+  const dbA = dbForTenant(a.id);
+
+  const countA = () => prisma.numberSequence.count({ where: { tenantId: a.id } });
+
+  try {
+    // (1) commit
+    await tenantTransaction(dbA, a.id, async (tx) => {
+      await tx.numberSequence.create({ data: { tenantId: a.id, key: "customer", prefix: "K-" } });
+      await tx.numberSequence.create({ data: { tenantId: a.id, key: "work_order", prefix: "A-" } });
+    });
+    check("(1) commit: both rows persisted", (await countA()) === 2, await countA());
+
+    // (2) rollback
+    try {
+      await tenantTransaction(dbA, a.id, async (tx) => {
+        await tx.numberSequence.create({ data: { tenantId: a.id, key: "report", prefix: "B-" } });
+        await tx.numberSequence.create({ data: { tenantId: a.id, key: "emergency", prefix: "N-" } });
+        throw new Error("boom");
+      });
+      check("(2) rollback: error propagated", false);
+    } catch (err) {
+      check("(2) rollback: error propagated", (err as Error).message === "boom", (err as Error).message);
+    }
+    check("(2) rollback: no rows from failed tx", (await countA()) === 2, await countA());
+
+    // (3) foreign tenant inside the tx
+    try {
+      await tenantTransaction(dbA, a.id, async (tx) => {
+        await tx.numberSequence.create({ data: { tenantId: a.id, key: "report", prefix: "B-" } });
+        const foreign = await prisma.numberSequence.create({ data: { tenantId: b.id, key: "customer", prefix: "K-" } });
+        await tx.numberSequence.update({ where: { id: foreign.id }, data: { prefix: "HACK-" } });
+      });
+      check("(3) foreign update rejected", false);
+    } catch {
+      check("(3) foreign update rejected", true);
+    }
+    const foreignRow = await prisma.numberSequence.findFirst({ where: { tenantId: b.id } });
+    check("(3) foreign row unchanged", foreignRow?.prefix === "K-", foreignRow?.prefix);
+    check("(3) own write of failed tx rolled back", (await countA()) === 2, await countA());
+
+    // (4) nested join
+    try {
+      await tenantTransaction(dbA, a.id, async (tx) => {
+        await tx.numberSequence.create({ data: { tenantId: a.id, key: "report", prefix: "B-" } });
+        await tenantTransaction(tx, a.id, async (inner) => {
+          await inner.numberSequence.create({ data: { tenantId: a.id, key: "emergency", prefix: "N-" } });
+        });
+        throw new Error("outer boom");
+      });
+    } catch {
+      /* expected */
+    }
+    check("(4) nested writes rolled back with outer tx", (await countA()) === 2, await countA());
+  } finally {
+    await prisma.numberSequence.deleteMany({ where: { tenantId: { in: [a.id, b.id] } } });
+    await prisma.auditLog.deleteMany({ where: { tenantId: { in: [a.id, b.id] } } });
+    await prisma.tenant.deleteMany({ where: { id: { in: [a.id, b.id] } } });
+    await prisma.$disconnect();
+  }
+
+  console.log(failures ? `\n${failures} Fehler` : "\nOK");
+  process.exit(failures ? 1 : 0);
+}
+
+main().catch((err) => {
+  const msg = String((err as Error)?.message ?? err);
+  if (/craftvia_app|password authentication|permission denied for role/i.test(msg)) {
+    console.log(`⚠ ÜBERSPRUNGEN: RLS-Verbindung nicht möglich (${msg.split("\n")[0]})`);
+    process.exit(0);
+  }
+  console.error(err);
+  process.exit(1);
+});
diff --git a/src/server/db.ts b/src/server/db.ts
index f75babc..b469b18 100644
--- a/src/server/db.ts
+++ b/src/server/db.ts
@@ -1,3 +1,4 @@
+import { AsyncLocalStorage } from "node:async_hooks";
 import { PrismaClient } from "@prisma/client";
 import { PrismaPg } from "@prisma/adapter-pg";
 
@@ -329,6 +330,11 @@ async function applyTenantGuard(
  * `app.tenant_id` transaktionslokal gesetzt wird (verworfen bei Commit/Rollback
  * → kein Leak über den Pool). Die Guard-Logik ist in beiden Pfaden identisch.
  */
+type TxClient = Parameters<Parameters<PrismaClient["$transaction"]>[0]>[0];
+
+/** Active tenant transaction for the current async call chain (RLS path only). */
+const tenantTx = new AsyncLocalStorage<{ tenantId: string; tx: TxClient }>();
+
 export function dbForTenant(tenantId: string) {
   if (!tenantId) throw new Error("dbForTenant: tenantId is required");
 
@@ -353,6 +359,26 @@ export function dbForTenant(tenantId: string) {
             );
           }
 
+          // Inside tenantTransaction(): run on the shared transaction (atomic, context set once).
+          const active = tenantTx.getStore();
+          if (active) {
+            if (active.tenantId !== tenantId) {
+              throw new Error("Tenant isolation violation: nested transaction for another tenant");
+            }
+            const txDelegate = (active.tx as unknown as Record<
+              string,
+              Record<string, (a: unknown) => Promise<unknown>>
+            >)[model.charAt(0).toLowerCase() + model.slice(1)];
+            return applyTenantGuard(
+              active.tx as unknown as DelegateSource,
+              tenantId,
+              model,
+              operation,
+              args,
+              (a) => txDelegate[operation](a),
+            );
+          }
+
           // RLS-Pfad: alles in EINER Transaktion des Basisclients, damit
           // Kontextsetzung und Ausführung garantiert auf derselben Connection
           // liegen. `tx` ist uneextendiert → keine Rekursion in die Extension.
@@ -381,3 +407,37 @@ export function dbForTenant(tenantId: string) {
 }
 
 export type TenantDb = ReturnType<typeof dbForTenant>;
+
+/**
+ * Run `fn` atomically for one tenant. ALWAYS use this (or `inTransaction` in services)
+ * instead of `db.$transaction(...)` for multi-step writes — atomic in both modes:
+ *  - Owner mode: interactive transaction of the guarded client (the extension applies to tx).
+ *  - RLS mode: one craftvia_app transaction with app.tenant_id set once; every operation of the
+ *    guarded client inside `fn` (same async call chain) runs on that transaction.
+ * Nested calls join the outer transaction.
+ */
+export async function tenantTransaction<T>(
+  db: TenantDb,
+  tenantId: string,
+  fn: (tx: TenantDb) => Promise<T>,
+  options?: { timeout?: number; maxWait?: number },
+): Promise<T> {
+  if (!RLS_ENFORCED) {
+    if (isTransactionClient(db)) return fn(db);
+    return db.$transaction((tx) => fn(tx as unknown as TenantDb), options) as Promise<T>;
+  }
+  const active = tenantTx.getStore();
+  if (active) {
+    if (active.tenantId !== tenantId) throw new Error("Tenant isolation violation: nested transaction for another tenant");
+    return fn(db);
+  }
+  return appBase!.$transaction(async (tx) => {
+    await tx.$executeRaw`SELECT set_config('app.tenant_id', ${tenantId}, true)`;
+    return tenantTx.run({ tenantId, tx }, () => fn(db));
+  }, options);
+}
+
+/** Interactive transaction clients have no $transaction method. */
+function isTransactionClient(db: TenantDb): boolean {
+  return typeof (db as unknown as { $transaction?: unknown }).$transaction !== "function";
+}
diff --git a/src/server/dsgvo/pii-fields.ts b/src/server/dsgvo/pii-fields.ts
index e49e28c..d7a1ffe 100644
--- a/src/server/dsgvo/pii-fields.ts
+++ b/src/server/dsgvo/pii-fields.ts
@@ -20,4 +20,33 @@ export interface PiiReference {
 export const PII_REFERENCE_FIELDS: readonly PiiReference[] = [
   { model: "AuditLog", field: "actorId" },
   { model: "NotificationPreference", field: "userId" },
+  // ── Craftvia domain (0002_craftvia_domain) ──
+  { model: "Customer", field: "createdById" },
+  { model: "Team", field: "leaderUserId" },
+  { model: "TeamMember", field: "userId" },
+  { model: "WorkOrder", field: "createdById" },
+  { model: "WorkOrder", field: "teamLeadUserId" },
+  { model: "WorkOrderAssignee", field: "userId" },
+  { model: "WorkOrderStatusChange", field: "actorId" },
+  { model: "ChecklistItem", field: "checkedById" },
+  { model: "MaterialUsage", field: "recordedById" },
+  { model: "WorkSession", field: "userId" },
+  { model: "TimeEntry", field: "userId" },
+  { model: "TimeEntry", field: "correctedById" },
+  { model: "ActivityNote", field: "authorId" },
+  { model: "Document", field: "uploadedById" },
+  { model: "Photo", field: "takenById" },
+  { model: "VoiceNote", field: "recordedById" },
+  { model: "Report", field: "createdById" },
+  { model: "Report", field: "teamApprovedById" },
+  { model: "Report", field: "approvedById" },
+  { model: "Signature", field: "capturedById" },
+  { model: "ImportJob", field: "importedById" },
+  { model: "ImportJob", field: "confirmedById" },
+  { model: "Notification", field: "userId" },
+  { model: "SyncOperation", field: "userId" },
+  { model: "SyncOperation", field: "resolvedById" },
+  { model: "AiGeneration", field: "createdById" },
+  // Free-text person data of END CUSTOMERS (Customer/Contact/Site/Signature.signerName) is
+  // tenant business data under data processing — not part of the employee subject export.
 ];
diff --git a/src/server/services/context.ts b/src/server/services/context.ts
index 29284d7..4e4eaa1 100644
--- a/src/server/services/context.ts
+++ b/src/server/services/context.ts
@@ -1,5 +1,5 @@
 import type { Session } from "next-auth";
-import type { TenantDb } from "@/server/db";
+import { tenantTransaction, type TenantDb } from "@/server/db";
 
 /**
  * Context passed to every domain service. Created by server actions (from moduleGuard)
@@ -23,6 +23,15 @@ export function ctxFromGuard(g: { session: Session; db: TenantDb; permissions: R
   };
 }
 
+/**
+ * Run a multi-step write atomically (ARCHITEKTUR §4.8). `fn` receives a ctx whose `db`
+ * is bound to the transaction; nested calls join the outer transaction.
+ * Never use `ctx.db.$transaction(...)` directly — it is not atomic with RLS_ENFORCED=true.
+ */
+export function inTransaction<T>(ctx: ServiceCtx, fn: (ctx: ServiceCtx) => Promise<T>): Promise<T> {
+  return tenantTransaction(ctx.db, ctx.tenantId, (tx) => fn({ ...ctx, db: tx }));
+}
+
 export function can(ctx: ServiceCtx, permission: string): boolean {
   return ctx.permissions.has(permission);
 }
diff --git a/src/server/services/imports/confirm.ts b/src/server/services/imports/confirm.ts
index 76bca1f..6ee359d 100644
--- a/src/server/services/imports/confirm.ts
+++ b/src/server/services/imports/confirm.ts
@@ -1,8 +1,7 @@
 import type { Prisma } from "@prisma/client";
-import type { TenantDb } from "@/server/db";
 import { writeAuditLog } from "@/server/audit";
 import { nextNumber } from "@/server/services/numbering";
-import { assertCan, ServiceError, type ServiceCtx } from "@/server/services/context";
+import { assertCan, inTransaction, ServiceError, type ServiceCtx } from "@/server/services/context";
 import { readStoredExtraction } from "@/lib/imports/extraction";
 import { computeCorrections, reviewFormSchema, type ReviewForm } from "@/lib/imports/review";
 // TODO(L3→L2): replace with the L2 work order service after merge (same input type).
@@ -65,9 +64,8 @@ export async function confirmImport(ctx: ServiceCtx, importId: string, rawForm:
   const corrections = computeCorrections(stored.fields, form);
   const now = new Date();
 
-  const result = await ctx.db.$transaction(async (tx) => {
-    const db = tx as unknown as TenantDb;
-    const txCtx: ServiceCtx = { ...ctx, db };
+  const result = await inTransaction(ctx, async (txCtx) => {
+    const db = txCtx.db;
 
     const switched = await db.importJob.updateMany({
       where: { id: job.id, status: "review_required" },