# .claude/hooks — enforcement, not advice

`CLAUDE.md` files can only ask. These hooks are the part that enforces, and they
travel with the repo so a session started anywhere in this checkout gets them.

They are wired up in `.claude/settings.json`.

| Hook | Event | What it does |
|---|---|---|
| `prod-guard.sh` | PreToolUse | Live-host commands: reads run unprompted, mutations ask first |
| `secrets-guard.sh` | PreToolUse | Denies any direct write to `infra/deploy/secrets/*.yaml` |
| `lint-after-edit.sh` | PostToolUse | shellchecks an edited `*.sh` and feeds findings back immediately |

## Why prod-guard exists

`agent` has passwordless sudo on prod and beta, and the operator's global settings
allow `Bash(ssh prod:*)` outright. Nothing about `ssh prod 'docker service rm …'`
goes through a pull request, so CI cannot see it — before this hook, any session in
any directory could delete production with no prompt.

**It classifies by allowlist, not blocklist.** Only commands positively recognised as
read-only are allowed through; everything else asks. A blocklist of dangerous verbs
is wrong by construction — the first destructive verb nobody thought of sails
straight through. Being wrong in the "ask" direction costs a keystroke; being wrong
the other way costs production.

Beta is guarded as strictly as prod: it serves beta.thermograph.org *and* hosts
Forgejo, so a destructive command there takes out git, CI and the registry at once.
The LAN dev box is deliberately unguarded.

## Changing the classifier

`is_readonly()` in `prod-guard.sh` splits a command on `&&`, `||`, `;` and `|`, then
checks each segment's leading word. Redirection to a file, command substitution,
`sed -i`, and mutating `docker`/`git`/`systemctl` subcommands all count as writes.

If you add a command to the allowlist, **re-run the test matrix**. There is a
non-obvious failure mode this already hit once: the loop is fed by
`printf '%s\n' | sed`, and dropping that trailing newline makes `read` return
non-zero on the only line, so the loop body never runs and *every* command
classifies as read-only — a silent, total bypass that still looks like it works.

Test by piping a payload straight in:

```bash
echo '{"tool_name":"Bash","tool_input":{"command":"ssh prod '\''rm -rf /'\''"}}' \
  | .claude/hooks/prod-guard.sh
# expect: permissionDecision "ask"
```

Exit 0 with no output means "no opinion" and the normal permission flow proceeds.
That is also what happens if `jq` is missing or the script errors, so a bug here
fails toward the prompt rather than toward silent execution.

## lint-after-edit needs shellcheck on PATH

It exits quietly when shellcheck is absent, so it is **inert until installed** — a
missing local tool must not break editing, and `shell-lint` CI is still the backstop.
Install the same pinned version CI uses:

```bash
VER=v0.11.0
curl -fsSL "https://github.com/koalaman/shellcheck/releases/download/${VER}/shellcheck-${VER}.linux.x86_64.tar.xz" \
  | tar -xJ --strip-components=1 -C ~/.local/bin "shellcheck-${VER}/shellcheck"
```