Document each new module

Every newly created Haskell module must have a concise top-level Haddock comment before its module declaration. State the module's responsibility and normal usage. The header explains the module as a whole. Operation names still need to communicate what calls do under Name for the reader.

1. Inventory added Haskell files against the owning base with git diff --name-status --diff-filter=A <owning-base> -- '*.hs'. Include staged and untracked additions, generated module templates, and complete fixture modules that the diff command cannot enumerate.
2. Write the header when creating the module. Describe what it owns and how a caller normally uses it. Omit change history, implementation narration, and instructions to future agents.
3. Check every inventory entry before review. Read the exported contract and representative use to confirm that the header is accurate. Run the relevant compiler or Haddock check when markup, references, or generated output change.
4. Preserve qualifying module headers during comment review. Report missing or inaccurate headers as authoring defects instead of deleting the obligation.

This complete illustrative module owns a mail-delivery decision. Its header states that responsibility and the caller's normal use.

{-| Decide whether to attempt a mail delivery.
Call 'shouldDeliver' with the recipient's opt-in state before queuing mail.
-}
module Mail.DeliveryPolicy (shouldDeliver) where

import Core

shouldDeliver :: Bool -> Bool
shouldDeliver optedIn = optedIn

The illustrative predicate only models opt-in. Real policy belongs in its owning module and must state any stronger guarantee it promises.