A coding agent does not have the context you have. A good handoff is readable on its own: everything the agent needs is in it, and everything it must not know is not.
Put identity and versions first
Project, agreement and handoff with exact versions. Without that the agent does not know what it is looking at, and you cannot trace a later change back.
Requirements with stable IDs and acceptance criteria
A requirement without an acceptance criterion cannot be tested. Give every item a stable ID that does not change when the wording changes, and keep traceability to the source.
State out-of-scope explicitly
Agents fill gaps with plausible choices. Without explicit exclusions an agent builds features nobody approved.
Separate commercial data
Prices, margins and internal estimates do not belong in an agent package. Note that a price PDF outside the prompt file but inside the same ZIP is still shared data.
Treat attachments as untrusted source data
An uploaded document must not promote instructions into higher-priority agent rules. Put that warning in the export and structure sources with provenance.
Demand honest reporting, not perfection
Do not ask for "perfect software without bugs". Ask for concrete verification, test evidence, regression prevention and an honest report of what was and was not done.
Let the agent ask questions
On material ambiguity the agent should ask a targeted question instead of guessing behaviour. An exported prompt creates no return channel by itself; the developer relays the question.