diff --git a/src/document-workbench/doc0-upload-client.ts b/src/document-workbench/doc0-upload-client.ts
index 1aa6eb8..05d1673 100644
--- a/src/document-workbench/doc0-upload-client.ts
+++ b/src/document-workbench/doc0-upload-client.ts
@@ -51,6 +51,45 @@ export type Doc0Inspection =
   | { status: 'not_found' | 'in_progress' | 'reconciliation_required' }
   | { status: 'completed_recorded'; documentId: string; versionId: string };
 
+/**
+ * DOC0 fingerprints the multipart parser's filename and MIME, not the values
+ * supplied to FormData. Use an ASCII wire name and a restricted, normalized
+ * MIME so their parser interpretation is deterministic. The original name is
+ * preserved separately as DOC0's displayName.
+ *
+ * Internal contract only: callers must retain this identity before dispatch,
+ * authorize its scope, and keep the same input bytes/metadata until dispatch.
+ */
+export function prepareDoc0UploadIdentity(input: Doc0UploadInput): {
+  sourceSha256: string;
+  sourceSizeBytes: number;
+  requestFingerprint: string;
+  wireFilename: string;
+  wireMimeType: string;
+} {
+  if (
+    ![input.tenantId, input.projectId, input.actorId, input.requestId, input.idempotencyKey, input.filename, input.mimeType]
+      .every((value) => typeof value === 'string' && value.trim()) ||
+    ![input.tenantId, input.actorId, input.requestId, input.idempotencyKey]
+      .every((value) => /^[\x21-\x7e]{1,256}$/.test(value)) ||
+    !['public', 'internal', 'confidential', 'restricted', 'personal-data', 'financial', 'legal'].includes(input.classification) ||
+    !(input.bytes instanceof Uint8Array) || input.bytes.byteLength === 0
+  ) throw new Error('Invalid DOC0 upload input');
+  const wireMimeType = input.mimeType.toLowerCase();
+  if (!/^[a-z0-9][a-z0-9!#$&^_.+-]*\/[a-z0-9][a-z0-9!#$&^_.+-]*$/.test(wireMimeType)) {
+    throw new Error('Invalid DOC0 upload MIME type');
+  }
+  const extension = /\.([a-z0-9]{1,16})$/i.exec(input.filename)?.[1]?.toLowerCase() ?? 'bin';
+  const wireFilename = `source.${extension}`;
+  const sourceSha256 = createHash('sha256').update(input.bytes).digest('hex');
+  const sourceSizeBytes = input.bytes.byteLength;
+  const requestFingerprint = createHash('sha256').update(JSON.stringify([
+    'doc0-upload-v1', input.tenantId, input.projectId, input.actorId, sourceSha256,
+    sourceSizeBytes, wireFilename, wireMimeType, input.filename, 'unknown', input.classification, [], null,
+  ])).digest('hex');
+  return { sourceSha256, sourceSizeBytes, requestFingerprint, wireFilename, wireMimeType };
+}
+
 const MAX_RECEIPT_BYTES = 128 * 1024;
 
 async function readBoundedJson(response: Response): Promise<unknown> {
@@ -108,26 +147,9 @@ export class Doc0UploadClient {
   }
 
   async upload(input: Doc0UploadInput): Promise<Doc0UploadReceipt> {
-    if (
-      ![
-        input.tenantId,
-        input.projectId,
-        input.actorId,
-        input.requestId,
-        input.idempotencyKey,
-        input.filename,
-        input.mimeType,
-      ].every((value) => typeof value === 'string' && value.trim()) ||
-      !['public', 'internal', 'confidential', 'restricted', 'personal-data', 'financial', 'legal'].includes(
-        input.classification,
-      ) ||
-      !(input.bytes instanceof Uint8Array) ||
-      input.bytes.byteLength === 0 ||
-      input.bytes.byteLength > this.options.maxBytes
-    ) {
-      throw new Error('Invalid DOC0 upload input');
-    }
-    const expectedHash = createHash('sha256').update(input.bytes).digest('hex');
+    const identity = prepareDoc0UploadIdentity(input);
+    if (identity.sourceSizeBytes > this.options.maxBytes) throw new Error('Invalid DOC0 upload input');
+    const expectedHash = identity.sourceSha256;
     const body = new FormData();
     body.set(
       'input',
@@ -138,7 +160,7 @@ export class Doc0UploadClient {
         classification: input.classification,
       }),
     );
-    body.set('file', new Blob([new Uint8Array(input.bytes)], { type: input.mimeType }), input.filename);
+    body.set('file', new Blob([new Uint8Array(input.bytes)], { type: identity.wireMimeType }), identity.wireFilename);
     let response: Response;
     try {
       response = await this.fetchImpl(`${this.baseUrl}/v1/doc0/documents`, {
diff --git a/tests/document-workbench/doc0-upload-client.test.ts b/tests/document-workbench/doc0-upload-client.test.ts
index ed2ed5e..36a04ca 100644
--- a/tests/document-workbench/doc0-upload-client.test.ts
+++ b/tests/document-workbench/doc0-upload-client.test.ts
@@ -1,6 +1,6 @@
 import { createHash } from 'node:crypto';
 import { describe, expect, it, vi } from 'vitest';
-import { Doc0UploadClient, Doc0UploadOutcomeUnknownError, Doc0InspectionUnavailableError } from '../../src/document-workbench/doc0-upload-client';
+import { Doc0UploadClient, Doc0UploadOutcomeUnknownError, Doc0InspectionUnavailableError, prepareDoc0UploadIdentity } from '../../src/document-workbench/doc0-upload-client';
 
 const bytes = new TextEncoder().encode('source bytes');
 const input = {
@@ -48,6 +48,39 @@ describe('DOC0 upload client', () => {
       pipelineStage: 'parsed',
     });
   });
+  it.each(['rapport åäö.xlsx', 'folder/name.txt', 'Back\\path.txt', 'A"B.txt', 'row\r\nname.txt'])(
+    'uses stable multipart metadata while retaining original name: %s', async (filename) => {
+      const fixture = { ...input, filename, mimeType: 'APPLICATION/PDF' };
+      const identity = prepareDoc0UploadIdentity(fixture);
+      const fetchImpl = vi.fn(async (_url: string | URL | Request, init?: RequestInit) => {
+        const form = init?.body as FormData;
+        expect(JSON.parse(form.get('input') as string).displayName).toBe(filename);
+        expect((form.get('file') as File).name).toBe(identity.wireFilename);
+        expect((form.get('file') as File).type).toBe('application/pdf');
+        return Response.json(receipt, { status: 201 });
+      });
+      await new Doc0UploadClient({ baseUrl: 'https://doc0.test', serviceToken: 'test', maxBytes: 100, fetchImpl }).upload(fixture);
+      expect(identity.sourceSha256).toBe(receipt.currentVersion.checksumSha256);
+      expect(identity.requestFingerprint).toMatch(/^[0-9a-f]{64}$/);
+      expect(fetchImpl).toHaveBeenCalledOnce();
+    },
+  );
+  it('rejects non-canonical identity headers before any upload', async () => {
+    const fetchImpl = vi.fn();
+    const client = new Doc0UploadClient({ baseUrl: 'https://doc0.test', serviceToken: 'test', maxBytes: 100, fetchImpl });
+    for (const tenantId of [' tenant-a', 'tenant-a ', 'tenant-å', 'tenant-\n']) {
+      await expect(client.upload({ ...input, tenantId })).rejects.toThrow(/Invalid/);
+    }
+    expect(fetchImpl).not.toHaveBeenCalled();
+  });
+  it('rejects ambiguous MIME values before any upload', async () => {
+    const fetchImpl = vi.fn();
+    const client = new Doc0UploadClient({ baseUrl: 'https://doc0.test', serviceToken: 'test', maxBytes: 100, fetchImpl });
+    for (const mimeType of ['text/plain; charset=utf-8', 'text/å', ' text/plain', 'not-a-mime']) {
+      await expect(client.upload({ ...input, mimeType })).rejects.toThrow(/MIME/);
+    }
+    expect(fetchImpl).not.toHaveBeenCalled();
+  });
   it.each([
     { document: { ...receipt.document, tenantId: 'tenant-b' } },
     { document: { ...receipt.document, projectId: 'other' } },