# Link URL Policy

## Purpose

`internal/link` defines shared validation for configured and persisted HTTP link URLs.

## Inputs and outputs

Input is a URL string. Output is either nil for an accepted URL or a concise validation error that callers wrap with field context.

## Validation behavior

Accepted URLs must parse successfully, use `http` or `https`, include a host, and omit query strings and fragments.

## Boundaries

This package validates URL shape only. It does not construct destination output URLs, choose primary URLs, infer public URLs from backend configuration, or read configuration files.

## Tests

Before changing link URL policy, inspect tests under `internal/link` and callers in `internal/config`, `internal/state`, and `internal/publish`.

## Invariants

- Configured `links.base_url`, persisted `links.primary_url`, persisted output `url`, and publish link planning use the same URL policy.
- Callers own field-specific error context.
- URL path construction remains in `internal/publish`.