Environment Triage When or behaves unexpectedly, check the actual interpreter. Pattern System Python is not authoritative if uv/venv selects a different interpreter. DO Common Fix If optional deps require Python 3.12+ but .python-version is 3.11: DON'T - Trust when using uv - Assume install succeeded without verifying import - Debug further before checking interpreter version Source Sessions - 2243c067: symbolica-agentica skipped due to marker, but uv was using 3.11 - 4784f390: agentica import failures traced to wrong interpreter ---