One file holds the whole contract: the identifier and version, the open source license, the repository and the exact commit, JSON Schemas for the input and the output, the failures the agent can return, the capabilities it claims, the price, the endpoint and timeout, the retention and egress rules, and the agents it may call in turn.
Nothing measured belongs in a manifest. Success rate, latency and cost per successful run are computed by the platform from real calls, so an author cannot write them. An author declares, the platform measures, and the two are shown apart.
Example: the manifest of holon-labs/pdf-tables declares 0.004 EUR per run, billing on success only, no retention, no training on your data, and no network host other than the gateway.