For 24 hours, every dashboard was green. Every launchd job reported exit 0, and the logs lined up neatly with (exit 0) on every row. Meanwhile, DM replies on X (formerly Twitter) were at zero for the entire day, and YouTrust was the same. The failures were happening. The exit codes just never made it back to the caller.
Back in university I stacked freelance gigs up to ¥600k/month, then got laid off and went back to zero. Over the following six months I built an autonomous Claude Code environment, and I'm now at ¥1.2M/month in revenue. This article is about the hook wiring that holds that environment together — more precisely, about the time I thought I'd wired it up and nothing was actually plugged in.
Why This Mechanism Works
Claude Code has two kinds of hook points: PreToolUse and Stop. PreToolUse interrupts right before Claude invokes a tool; Stop runs right before Claude tries to finish a response. If a hook script returns exit 1, Claude blocks that tool call or Stop action — by specification.
When I learned about this, I immediately wanted to use it as a guardrail for my automation environment. "Don't let an implementation be marked complete without an audit." "Stop if a secret is about to slip into a commit." "Cancel the Action if a designated script fails." You write these in code and control Claude's behavior from the outside.
