Cookbook: write a recipe for an agent that does not have one

[arpanghoshal]

The cookbook has 22 recipes. Each one is a single consequential action, the policy that
governs it, and a runnable example. The ones below have no recipe and would each make a good
first contribution.

Claim one in a comment before you start so two people don't write the same page.

Recipe	Category	The action worth gating
A subscription-cancellation agent	Money	Cancelling or refunding a plan mid-term, with a tier where a human answers
A price or inventory-change agent	Money	A price write that a fat-fingered decimal makes catastrophic
A DNS-record change agent	Infrastructure	An A or MX change that takes a domain off the internet
A feature-flag rollout agent	Infrastructure	Moving a flag to 100% of traffic
A document-sharing agent	Permissions	Granting access to somebody outside the organisation
A payroll-change agent	Records	Editing an amount that reaches a bank file

What a recipe is

Read two or three existing ones first — refund-agent.mdx
is the shortest, data-deletion-agent.mdx shows a
constraint carrying the interesting part. Each has: the action, the policy YAML, the decorated
function, what happens when the guard fires, and what CTRLRun does not do for that scenario.

Done means

• The page is in docs/cookbook/, linked from docs/cookbook/index.mdx under its category.
• Every fenced block marked runnable executes offline and exits 0 — tools/docs_audit/
  runs them in CI with a socket guard. A sample either runs or is not marked.
• Behind every expected refusal, an else that fails. A sample that asserts a refusal
  raises on the path where the refusal did not happen. Documentation that quietly starts
  succeeding is worse than none.
• docs/STYLE.md — run the four checks in its last section before opening the PR.
• No compliance or standards language anywhere in it. The forbidden-words lint will tell you,
  but the rule is in CONTRIBUTING.md and it is not negotiable.

A recipe not on this list is welcome too, if it is a real action that can move money, delete
infrastructure or grant permissions. Say which one in a comment first.