fix: auto-add --disable-extensions-except for --load-extension in args

[onepaperbox]

Problem

When Chrome extensions are loaded via --load-extension in args/extra_args (e.g., through CloakBrowser-Managers launch_args), extensions fail to load because Playwrights default --disable-extensions flag blocks all extensions.

The extension_paths parameter (added in #210) already handles this correctly by injecting both --load-extension and --disable-extensions-except. However, when --load-extension is passed via args directly (as CloakBrowser-Manager does), the companion --disable-extensions-except flag is not automatically injected, leaving extensions broken.

This affects all CloakBrowser-Manager users who try to load extensions via launch_args. Related issues:

• Failed to load extensions with launch args CloakBrowser-Manager#30
• Unable to install Chrome Web Store extensions CloakBrowser-Manager#37

Fix

In build_args(), after processing extension_paths, check if --load-extension exists in the seen dict (from extra_args) but --disable-extensions-except does not. If so, automatically inject the companion flag with the same paths.

This makes extension loading work seamlessly via either:

1. extension_paths=["/path/to/ext"] — existing, unchanged behavior
2. args=["--load-extension=/path/to/ext"] — now auto-fixed

Files changed:

• cloakbrowser/browser.py — Python build_args() — auto-inject companion flag
• js/src/args.ts — JS buildArgs() — same logic
• tests/test_build_args.py — 5 new Python tests
• js/tests/extension-loading.test.ts — 4 new JS tests

Testing

All 43 Python tests pass, all 5 JS tests pass:

tests/test_build_args.py::test_load_extension_auto_adds_companion PASSED
tests/test_build_args.py::test_load_extension_multi_path_auto_adds_companion PASSED
tests/test_build_args.py::test_load_extension_no_duplicate_companion PASSED
tests/test_build_args.py::test_no_companion_without_load_extension PASSED
tests/test_build_args.py::test_extension_paths_still_works PASSED

js/tests/extension-loading.test.ts (5 tests) PASSED

Backward Compatibility

• Existing extension_paths parameter behavior is unchanged (the elif only fires when extension_paths is falsy)
• If users already manually include --disable-extensions-except in their args, no duplication occurs (checked via seen dict)
• No API changes, no new parameters