The QA Margin Curve: Why Testing Tooling Decides Which Agency Retainers Survive

QA tooling is the cheapest lever an agency has on revision-cycle cost, because every annotated client comment replaces an email thread and every automated regression check replaces a billable re-test. The economics cut both ways: bundled QA raises retainer value, but test suites that grow faster than the code they guard turn fixed-bid delivery into unpaid maintenance. The agencies winning 2026 work are the ones that can show a client a passing checkout flow on every deploy, not the ones with the largest test count.