We get a few not infinite. with a Claude 5x Max subscription I get 3-5 workable parallel agents that themselves spawn subagents to complete work in a ~3 hour window before tokens are spent. I imagine with 20x Max that could be increased to maybe 10 within a 5 hour window? so if you want infinite you're also talking infinite money. Working in parallel takes me personally to a higher plane of output than that of a 10x engineer as it pertains to fulfilling requirements.
Modern agents can write tests that are meaningful and require the agent to pass them with any change to avoid regressions. Humans can review the code/test the downstream application to ensure it works as intended.
It rarely takes a single prompt to get something done, but the agents can figure out as long as the human is specific about what constitutes accurate.