Strong writeup, and the billable response rule in section 3 is the part most listings get wrong. What I would add is retries: an agent that times out and reissues the call pays twice unless the listing accepts an idempotency key and the charge is recorded against that key rather than the attempt. The other unaddressed layer is settlement. Micro USD pricing works fine on a ledger, but the agent still needs a funded source it can spend from with a per task cap, and the provider wants confirmation that value actually moved before returning a 200 instead of reconciling an invoice afterwards. That is where a per agent payment address with developer set caps does more work than a prepaid balance, which is the bet CAI makes.