2 parts · July 27, 2026 — read in order, start to finish.
The loop every tutorial shows you is five lines. The loop that survives a real agent is defined by its edges — four message-shape rules the API enforces with a 400, and four stopping conditions that keep it from running forever.
Your loop checks for one stop_reason and assumes the rest never happen. Then max_tokens truncates a tool call mid-JSON, pause_turn strands a web search, and a refusal returns empty content — and your agent hangs or crashes. Here's what each of the six actually means and what to do about it.
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