Marketing harness
A marketing harness is everything in an AI agent except the model.
A model starts every task knowing nothing about your brand, your approved claims, or who signs off on what. The harness gives it that knowledge, the tools, and the checks on every run.
A marketing harness needs more of your reviewers' judgment written down as rules than a coding one. Software has many checks with one right answer, such as tests that pass or fail. Marketing quality is mostly a judgment spread across many reviewers, and a sent email or spent budget can't be undone.
The harness is part owned and part rented. Your brand's rules, claims, reviewers' reasons, and lessons stay yours. You rent the model and the agent platform the loops run on, and the model is a part you can swap.
Example
In an invented example, a performance marketing team is making paid social ads for one client and three audiences. The drafting agent reads the client's request and each audience's rules. When the brand lead rejects an image because the client always shows its product in use, that reason goes into the lessons file the next run reads.