Bonus 6. A rule you wrote down can be forgotten, misread, or reasoned around at two in the morning. A reflex cannot. This is how you build the things that simply refuse.
You wrote in CLAUDE.md: never touch the camera originals.
That is an instruction. It is read, it is understood, and it is followed almost always.
Almost always is not the same as always, and the one time it is not followed is the time you had one copy of the rushes.
It sits between the intention and the machine, looks at what is about to happen, and says no.
It cannot be persuaded, because it is not listening.
Something is about to happen. Before it does, your script gets a look at it and can stop it.
| Moment | What you use it for |
|---|---|
| before a command runs | refuse the dangerous ones |
| before a file is written | refuse secrets, refuse protected folders |
| when a session starts | brief yourself on where things stand |
| when a session ends | save, log, tidy |
The first two are safety. The second two are convenience. Build the first two.
In Module 0 of the main course, you watched something refuse a destructive command.
That was one of these. You have already seen it work, which means the rest of this deck is about writing your own rather than about trusting the idea.
A small script. It receives what is about to happen, and it exits with a code that either allows or blocks.
#!/usr/bin/env bash
# Refuse anything that would touch the camera originals.
if echo "$1" | grep -q "_originals"; then
echo "BLOCKED: _originals is read only. Nothing writes there, ever."
exit 1 # non-zero stops it
fi
exit 0 # zero lets it throughNon-zero means no. That is the entire contract.
"Write me a guard that blocks any command touching _originals, explain each line in plain English, and tell me exactly how to test that it works."
Ask for the explanation and the test in the same sentence. A guard you cannot read is a guard you cannot trust, and a guard you have not seen fire is not a guard.
{
"hooks": {
"PreToolUse": [
{ "matcher": "Bash", "command": ".claude/hooks/originals_guard.sh" }
]
}
}In your settings file, the same one from Bonus 3. Names of the moments change between versions, so ask rather than copy:
"Read the current documentation and tell me the exact configuration to run this script before any command executes, for the version I have installed."
Break it on purpose. Today. While the stakes are zero.
Ask for something the guard should refuse. Watch it refuse.
If it does not, you have learned something enormous for the price of thirty seconds, and you have learned it now rather than during a delivery week.
"Try to do the thing my guard should refuse, and tell me exactly what happened."
Thirty seconds. Put it in the monthly audit with the memory decay check.
Refuses recursive deletes, and refuses anything deleting outside the project folder.
Not "asks about." Refuses. There is no legitimate reason for an automated pass to remove a tree of files, and the one time there is, you can do it yourself with your own hands.
Looks at anything about to be written and refuses if it contains something shaped like a password, a key or a token.
This one saves you from yourself. The realistic way a credential leaks is not an attack. It is being pasted into a config file, committed, and pushed, in about four seconds, by someone helpful.
Whatever your irreplaceable thing is. Camera media, masters, delivered files, the archive.
The folder you must protect is the one you never think about, because you never touch it. That is precisely why an automated pass will reach it before you notice.
They are not for taste, style or quality. They are for the irreversible.
A guard that blocks things you merely dislike will fire constantly, and a guard that fires constantly gets switched off, taking the two that mattered with it.
Every guard you add makes the whole set slightly more likely to be disabled in frustration. Three good ones beat fifteen.
Once safety is handled, the same mechanism does pleasant things:
Nice, and genuinely useful. But build them second, and never let them delay the three above.
Thirty minutes, and this is the half hour that makes everything else safe.
how to test it."*
Your rules became reflexes, and reflexes do not have bad nights.
Teaching It a Procedure. Writing down how you do a thing once, so it is done your way every time without you being in the room.
Verified against Claude Code 2.1.220 · 2026-07-30.