The agents that buy things need the strongest budgets
Procurement and purchasing agents exist to spend — one unvetted vendor, one wrong purchase. Why the buying agents get the tightest rules.
Most agents spend as a side effect of doing work. Procurement agents spend as the point of their existence — they source, compare, and buy. The rules that fit a coding agent don't fit them.
The buying agent's risk profile
Purchasing is irreversible and vendor-directed: one unvetted merchant, one approved purchase, and procurement has happened. There's no retry to catch — the buy is the event.
The tightest controls
The allowlist is the centerpiece — unapproved vendors are simply not payable. Then a per-requisition cap, an approval threshold for new vendors, and a full audit trail on every purchase. Buy with the strongest budget, always.