Start with the facts that change decisions
Name the application entry points, the package or service you are working on, and one nearby implementation that reflects current conventions. Include the usual verification commands and any required local services. Avoid copying the entire file tree; it rarely explains which parts matter for the next task.
Give every important note a source
A statement such as "the service owns validation" should point to the relevant code or project instruction. Mark assumptions and open questions separately. When the repository changes, revisit the note before reusing it. A context document is a useful orientation aid, not a guarantee that every detail remains current.