fix(python): support @typechecked decorator

[pyranota]

WindmillFinder's ModuleSpec lacked origin, so file was never set on loaded modules. inspect.getfile() then raised "is a built-in module", breaking typeguard's @TypeChecked and anything else that introspects module source. Use spec_from_file_location() which sets origin correctly.

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PR Review: fix @TypeChecked decorator in Python relative imports

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• Review code quality, bugs, security, performance
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Summary

Clean, well-scoped fix. The root cause is correctly identified: ModuleSpec(name, SourceFileLoader(name, fullpath)) doesn't set spec.origin, so module.__file__ is never populated. spec_from_file_location(name, fullpath) sets origin (and has_location=True), which means inspect.getfile() works correctly — fixing @typechecked and any other decorator/tool that introspects module sources.

Code Review

loader.py changes — looks good. Both call sites (line 37: local cache hit, line 66: freshly downloaded) are updated consistently. spec_from_file_location internally creates a SourceFileLoader under the hood, so behavior is otherwise identical.

Minor nit: SourceFileLoader is still imported on line 4 but is no longer used directly. Consider removing it to keep the imports clean:

from importlib.machinery import ModuleSpec

Fix this →

Test (python_jobs.rs) — well structured. The test creates a helper script via SQL fixture that uses inspect.getfile() (the same mechanism typeguard uses), then imports it from another script. The assertion starts_with("Hello, World! from ") correctly validates that __file__ was set without being brittle about the exact path. Good approach.

Fixture (typechecked_python.sql) — clean and minimal. Hash 12349 doesn't collide with existing fixtures.

No Issues Found

The change is minimal, correct, and well-tested. No security, performance, or correctness concerns.

Testing Instructions

To verify this fix, create two Python scripts in a Windmill workspace. First, create a helper script at path f/system/typechecked_helper with content that uses inspect.getfile(sys.modules[__name__]) and returns the result (or uses @typechecked from typeguard). Then create a second script that does from f.system.typechecked_helper import greet and calls the imported function. Run the second script — it should succeed without raising "<module> is a built-in module" errors. Previously, inspect.getfile() would fail because __file__ was not set on dynamically loaded Windmill modules.