Problem

dialyxir is listed as a test dependency but Dialyzer is not run in the Anvil CI pipeline (.anvil.yml). Typespecs exist in the codebase but are never machine-verified.

Impact

• Type errors go undetected
• Typespecs may be stale or incorrect
• False sense of type safety

Acceptance Criteria

• Add mix dialyzer step to .anvil.yml
• PLT cache configured to avoid rebuilding on every CI run
• All existing dialyzer warnings resolved (zero warnings)
• Any new warning fails the build