lake exe leanPython hangs on any Python file input

[pirapira]

Description

Running lake exe leanPython <file.py> hangs indefinitely on any Python file, including trivial ones. The lake test suite (which uses #eval assertPy) works correctly.

# Hangs forever:
echo 'print("hello")' > /tmp/test.py
timeout 15 lake exe leanPython /tmp/test.py  # killed by timeout

# Even simpler:
echo 'x = 1' > /tmp/test2.py
timeout 15 lake exe leanPython /tmp/test2.py  # killed by timeout

# But lake test passes fine:
lake test  # all tests pass

Expected Behavior

lake exe leanPython file.py should parse and interpret the file, printing output to stdout.

Actual Behavior

The process hangs indefinitely with no output. Requires kill/timeout to terminate.

Notes

• lake build succeeds
• All #eval assertPy tests pass via lake test
• The hang appears to be in the executable startup or file reading path, not in the interpreter itself
• This is a pre-existing issue (not introduced by recent changes)