Let a repository add to a prompt without forking it

[RobYed]

Project rules already reach the agents without being written down twice: the runtime loads AGENTS.md (or CLAUDE.md) on its own, and the prompts say a rule written there outranks the agent's general expectations. That covers most of what a repository wants to say.

What it does not cover is guidance that belongs to one agent and is not a project rule — "this repository's security review should always check the tenant condition on cached queries", say. Today the only way to add that is to fork the prompt, and then no fix to it ever arrives.

What to build

An optional file in the consumer's repository, for example .github/pitcrew/<agent-id>.md, whose contents are appended to the package's prompt.

Appended, not merged: a consumer who could rewrite the prompt could rewrite the part that says the diff is data rather than instruction.

Open questions

• Where the file lives, and whether the path is configurable.
• What happens on the comment trigger, where the run starts on the default branch. The addition should probably come from the same branch the rest of the configuration does, for the reason in docs/adr/0003-configuration-is-generated-by-the-package.md.
• A size limit, so an addition cannot quietly become most of the prompt.
• Whether the addition is shown in the run summary. It should be: an agent that behaves oddly is much easier to explain when what it was told is on the page.