TypeSpec & Dialyzer

RULES — Follow these with no exceptions

1. Run Dialyzer in CI — catch type errors before they reach production
2. Start with core modules — add typespecs incrementally, don't try to type everything at once
3. Never ignore Dialyzer warnings without documenting why — use .dialyzer_ignore.exs

Basic TypeSpecs

defmodule MyApp.Accounts do
  alias MyApp.Accounts.User