Add default-prefix constant usage architecture guard

Co-authored-by: Shri Sukhani <shrisukhani@users.noreply.github.com>

Author: cursoragent

CONTRIBUTING.md

@@ -135,6 +135,7 @@ This runs lint, format checks, compile checks, tests, and package build.
   - `tests/test_extension_request_internal_reuse.py` (extension request-helper internal reuse of shared model request helpers),
   - `tests/test_extension_route_constants_usage.py` (extension manager route-constant usage enforcement),
   - `tests/test_extract_payload_helper_usage.py` (extract start-payload helper usage enforcement),
+  - `tests/test_file_message_default_constant_usage.py` (extension/session file-message default-prefix constant usage enforcement),
   - `tests/test_file_message_prefix_literal_boundary.py` (extension/session file-message prefix literal centralization in shared metadata modules),
   - `tests/test_file_open_error_helper_import_boundary.py` (shared file-open error-message helper import boundary enforcement),
   - `tests/test_file_open_error_helper_usage.py` (shared file-open error-message helper usage enforcement),

tests/test_architecture_marker_usage.py

@@ -50,6 +50,7 @@
     "tests/test_model_request_wrapper_internal_reuse.py",
     "tests/test_tool_mapping_reader_usage.py",
     "tests/test_display_helper_usage.py",
+    "tests/test_file_message_default_constant_usage.py",
     "tests/test_file_message_prefix_literal_boundary.py",
     "tests/test_file_open_error_helper_import_boundary.py",
     "tests/test_file_open_error_helper_usage.py",

tests/test_file_message_default_constant_usage.py

@@ -0,0 +1,50 @@
+from pathlib import Path
+
+import pytest
+
+pytestmark = pytest.mark.architecture
+
+
+MODULE_EXPECTATIONS = (
+    (
+        "hyperbrowser/client/managers/extension_create_utils.py",
+        (
+            "EXTENSION_DEFAULT_MISSING_FILE_MESSAGE_PREFIX",
+            "EXTENSION_DEFAULT_NOT_FILE_MESSAGE_PREFIX",
+        ),
+    ),
+    (
+        "hyperbrowser/client/managers/sync_manager/extension.py",
+        ("EXTENSION_DEFAULT_OPEN_FILE_ERROR_PREFIX",),
+    ),
+    (
+        "hyperbrowser/client/managers/async_manager/extension.py",
+        ("EXTENSION_DEFAULT_OPEN_FILE_ERROR_PREFIX",),
+    ),
+    (
+        "hyperbrowser/client/managers/session_upload_utils.py",
+        (
+            "SESSION_DEFAULT_UPLOAD_MISSING_FILE_MESSAGE_PREFIX",
+            "SESSION_DEFAULT_UPLOAD_NOT_FILE_MESSAGE_PREFIX",
+            "SESSION_DEFAULT_UPLOAD_OPEN_FILE_ERROR_PREFIX",
+        ),
+    ),
+)
+
+FORBIDDEN_DEFAULT_PREFIX_LITERALS = (
+    'default_prefix="Extension file not found at path"',
+    'default_prefix="Extension file path must point to a file"',
+    'default_prefix="Failed to open extension file at path"',
+    'default_prefix="Upload file not found at path"',
+    'default_prefix="Upload file path must point to a file"',
+    'default_prefix="Failed to open upload file at path"',
+)
+
+
+def test_file_message_helpers_use_shared_default_prefix_constants():
+    for module_path, expected_constant_names in MODULE_EXPECTATIONS:
+        module_text = Path(module_path).read_text(encoding="utf-8")
+        for constant_name in expected_constant_names:
+            assert constant_name in module_text
+        for forbidden_literal in FORBIDDEN_DEFAULT_PREFIX_LITERALS:
+            assert forbidden_literal not in module_text