I had a gut feeling that my general-purpose subagent was the slow one. Then I measured it: 18 seconds on average, faster than Explore at 22. The real drag was code-reviewer at 37 seconds. Changing one habit based on that number dropped my weekly Claude Code spend by roughly 15–20%.
I made a couple hundred thousand yen a month as a student juggling side gigs, got laid off and went back to zero, and spent six months building an autonomous Claude Code setup that now runs at about ¥1.2M in monthly revenue. The foundation of that setup is post-session log collection driven by a Stop hook. This post covers the implementation, the 12 pitfalls I hit along the way, and the jq recipes I use every week.
Why this works
After using Claude Code for a while, a nagging feeling sets in: "I have no idea where the cost is going." You mix Explore agents, code-reviewer agents, general-purpose agents, and before you know it a session has been running for tens of minutes. But which agent is slow? Which one errors most often? I had never seen a number.
Saying "that agent feels heavy" is not data. Without data, you can't tell what to fix. For someone shipping systems solo at volume, that's a fatal blind spot. Optimizing a workflow starts with measuring it.
