The boring secret to a cheap AI coding agent — a byte-stable prompt prefix

I tried using Claude Code for a few weeks and quietly stopped. Not because it was bad — it's great — but because I'd hesitate before kicking off any non-trivial task, doing the math on what a 30-minute debugging session would cost. That's the wrong incentive for an agent. The whole pitch of "let it run" depends on the bill not scaring you. So I went the other direction. I built Reasonix — same shape as Claude Code or Aider, runs in your terminal, plan mode, tool calls, MCP — but it only talks to