test: strengthen Content-Disposition header assertions

- v2/test_files.py: expected_rfc5987 now includes the file extension so a
  regression that strips the extension from the RFC 5987 value is detected
- test_database.py: strengthen the dual-flow download assertion to verify
  both filename= and filename*= params are present, not just the prefix
- test_database.py: rename test_download_flows_non_ascii_content_disposition
  to test_download_flows_content_disposition_dual_param and update the
  docstring to accurately reflect that the ZIP filename is always ASCII
  (timestamp-based); the test now verifies the dual-param format

Author: AntonioABLima

src/backend/tests/unit/api/v2/test_files.py

@@ -625,11 +625,11 @@ async def test_unique_filename_path_storage(files_client, files_created_api_key)
 @pytest.mark.parametrize(
     ("filename", "expected_rfc5987"),
     [
-        ("龙.txt", "%E9%BE%99"),
-        ("测试文件.txt", "%E6%B5%8B%E8%AF%95%E6%96%87%E4%BB%B6"),
-        ("日本語ファイル.txt", "%E6%97%A5%E6%9C%AC%E8%AA%9E%E3%83%95%E3%82%A1%E3%82%A4%E3%83%AB"),
-        ("arquivo_com_acentuação.txt", "arquivo_com_acentua%C3%A7%C3%A3o"),
-        ("normal_file.txt", "normal_file"),
+        ("龙.txt", "%E9%BE%99.txt"),
+        ("测试文件.txt", "%E6%B5%8B%E8%AF%95%E6%96%87%E4%BB%B6.txt"),
+        ("日本語ファイル.txt", "%E6%97%A5%E6%9C%AC%E8%AA%9E%E3%83%95%E3%82%A1%E3%82%A4%E3%83%AB.txt"),
+        ("arquivo_com_acentuação.txt", "arquivo_com_acentua%C3%A7%C3%A3o.txt"),
+        ("normal_file.txt", "normal_file.txt"),
     ],
 )
 async def test_download_file_non_ascii_content_disposition(
@@ -657,8 +657,9 @@ async def test_download_file_non_ascii_content_disposition(
     assert expected_rfc5987 in content_disposition
     rfc5987_value = content_disposition.split("filename*=UTF-8''")[-1].split(";")[0].strip()
     decoded = unquote(rfc5987_value)
-    # The original filename stem must appear in the server-returned decoded name
+    # The decoded RFC 5987 value must contain both the stem and the extension
     assert filename.rsplit(".", 1)[0] in decoded
+    assert decoded.endswith(".txt")
 
 
 async def test_batch_download_files_non_ascii_content_disposition(files_client, files_created_api_key):

src/backend/tests/unit/test_database.py

@@ -562,15 +562,24 @@ async def test_download_file(
     # Check response data
     # Since the endpoint now returns a zip file, we need to check the content type and the filename in the headers
     assert response.headers["Content-Type"] == "application/x-zip-compressed"
-    assert "attachment; filename=" in response.headers["Content-Disposition"]
+    content_disposition = response.headers["Content-Disposition"]
+    assert "attachment" in content_disposition
+    assert 'filename="' in content_disposition
+    assert "filename*=UTF-8''" in content_disposition
 
 
 @pytest.mark.usefixtures("session")
-async def test_download_flows_non_ascii_content_disposition(client: AsyncClient, logged_in_headers):
-    """Downloading multiple flows must produce RFC 5987-encoded Content-Disposition for non-ASCII flow names."""
+async def test_download_flows_content_disposition_dual_param(client: AsyncClient, logged_in_headers):
+    """Downloading multiple flows must produce a dual-param RFC 5987 Content-Disposition header.
+
+    The ZIP filename is always timestamp-based (pure ASCII). This test verifies
+    that both the legacy 'filename=' param and the RFC 5987 'filename*=' param
+    are present and well-formed, as required for compatibility with both old
+    and new HTTP clients.
+    """
     from urllib.parse import unquote
 
-    # Create two flows with Chinese names
+    # Create two flows (names don't affect the ZIP filename, which is timestamp-based)
     chinese_names = ["龙流程", "测试下载"]
     flow_ids = []
     for name in chinese_names:
@@ -591,9 +600,11 @@ async def test_download_flows_non_ascii_content_disposition(client: AsyncClient,
     assert download_response.headers["Content-Type"] == "application/x-zip-compressed"
 
     content_disposition = download_response.headers["Content-Disposition"]
+    # Must include both params: ASCII fallback and RFC 5987
     assert "attachment" in content_disposition
+    assert 'filename="' in content_disposition
     assert "filename*=UTF-8''" in content_disposition
-    # The RFC 5987 value must be decodable and produce a valid filename
+    # The RFC 5987 value must decode to a .zip filename
     rfc5987_value = content_disposition.split("filename*=UTF-8''")[-1].split(";")[0].strip()
     decoded = unquote(rfc5987_value)
     assert decoded.endswith(".zip")