AgentKit vs LangChain vs Direct HTTP — picking the right integration for paid agent APIs

When you're plugging an LLM agent into an external API, you have three reasonable patterns: hand-rolled HTTP, AgentKit's action provider model, or LangChain's tool calling. They all work. They produce identical outputs against the same input. So which one should you actually use? I built the exact same agent three different ways - answering the same Kelly Criterion question - and the answer to "which one" depends on your stack, your team, and (most underrated) your wallet model. Here's the honest comparison.