feat(07-04): POST /classify re-queues Celery, removes synchronous classify (D-11)

- Replace synchronous await classifier.classify_document() with extract_and_classify.delay()
- Set doc.status='processing' and commit before dispatching Celery task
- Return {'document_id': str, 'status': 'processing'} instead of assigned topics
- Promote test_reclassify_requeues_celery from xfail stub to passing test
- Add test_reclassify_cross_user_returns_404 for IDOR security invariant (T-07-10)

backend/tests/test_documents.py

@@ -926,10 +926,107 @@ async def test_delete_cloud_remove_only(async_client, auth_user, db_session):
 
 
 # ---------------------------------------------------------------------------
-# Phase 7 Wave 0 xfail stub — D-11 re-classify endpoint
+# Phase 7 Plan 04 — D-11 re-classify endpoint (POST /{id}/classify → Celery)
 # ---------------------------------------------------------------------------
 
 
-@pytest.mark.xfail(strict=False, reason="Wave 0 stub — promoted in Plan 07-04")
-async def test_reclassify_requeues_celery():
-    pytest.xfail("not implemented yet — Plan 07-04")
+async def test_reclassify_requeues_celery(async_client, auth_user, db_session, monkeypatch):
+    """POST /api/documents/{id}/classify sets doc.status='processing', enqueues
+    Celery task via extract_and_classify.delay, and returns {'document_id': ...,
+    'status': 'processing'}.
+
+    D-11: reclassify endpoint triggers async processing instead of running
+    synchronously. The previous synchronous call to classifier.classify_document()
+    is replaced by extract_and_classify.delay(doc_id).
+    """
+    import uuid as _uuid
+    from unittest.mock import MagicMock
+    from db.models import Document
+
+    # Patch Celery delay to avoid real broker
+    mock_delay = MagicMock()
+    monkeypatch.setattr("tasks.document_tasks.extract_and_classify.delay", mock_delay)
+
+    # Create a document owned by auth_user
+    doc_id = _uuid.uuid4()
+    doc = Document(
+        id=doc_id,
+        user_id=auth_user["user"].id,
+        filename="reclassify_test.txt",
+        content_type="text/plain",
+        size_bytes=100,
+        storage_backend="minio",
+        status="uploaded",
+        object_key=f"{auth_user['user'].id}/{doc_id}/{_uuid.uuid4()}.txt",
+    )
+    db_session.add(doc)
+    await db_session.commit()
+
+    resp = await async_client.post(
+        f"/api/documents/{doc_id}/classify",
+        headers=auth_user["headers"],
+    )
+    assert resp.status_code == 200, resp.text
+    data = resp.json()
+    assert data["status"] == "processing", f"Expected status=processing: {data}"
+    assert data["document_id"] == str(doc_id), f"Expected document_id={doc_id}: {data}"
+
+    # Celery task was dispatched once with the doc's string ID
+    mock_delay.assert_called_once_with(str(doc_id))
+
+    # DB row was updated to processing
+    await db_session.refresh(doc)
+    assert doc.status == "processing", f"Expected doc.status=processing, got {doc.status}"
+
+
+async def test_reclassify_cross_user_returns_404(async_client, auth_user, db_session):
+    """POST /api/documents/{other_user_doc_id}/classify by a different user returns 404.
+
+    T-07-10 / D-16: cross-user reclassify attempt must return 404 (not 403) to
+    avoid information leakage. _get_owned_doc ownership check enforces this.
+    """
+    import uuid as _uuid
+    from db.models import Document, User, Quota
+    from services.auth import hash_password, create_access_token
+
+    # Create a document owned by auth_user
+    doc_id = _uuid.uuid4()
+    doc = Document(
+        id=doc_id,
+        user_id=auth_user["user"].id,
+        filename="other_user_doc.txt",
+        content_type="text/plain",
+        size_bytes=100,
+        storage_backend="minio",
+        status="uploaded",
+        object_key=f"{auth_user['user'].id}/{doc_id}/{_uuid.uuid4()}.txt",
+    )
+    db_session.add(doc)
+
+    # Create User B
+    user_b_id = _uuid.uuid4()
+    user_b = User(
+        id=user_b_id,
+        handle=f"classify_idor_{user_b_id.hex[:8]}",
+        email=f"classify_idor_{user_b_id.hex[:8]}@example.com",
+        password_hash=hash_password("Testpassword123!"),
+        role="user",
+        is_active=True,
+        password_must_change=False,
+    )
+    quota_b = Quota(user_id=user_b_id, limit_bytes=104857600, used_bytes=0)
+    db_session.add(user_b)
+    db_session.add(quota_b)
+    await db_session.commit()
+
+    token_b = create_access_token(str(user_b_id), "user")
+    headers_b = {"Authorization": f"Bearer {token_b}"}
+
+    # User B attempts to reclassify User A's document — must get 404
+    resp = await async_client.post(
+        f"/api/documents/{doc_id}/classify",
+        headers=headers_b,
+    )
+    assert resp.status_code == 404, (
+        f"Expected 404 for cross-user reclassify, got {resp.status_code}: {resp.text}"
+    )