The assertions

A rule reads a command before it runs. An assertion checks what a command that already reported success actually did.

The two halves are not the same job. pipe-to-tail can refuse git push … | tail -5 because the mistake is visible in the command string. Nothing in a command string tells you that the push you just ran reported Everything up-to-date about a branch you were not on.

Only successful calls

Claude Code sends a failed tool call to PostToolUseFailure, an event this crate ignores. So everything an assertion sees claimed to work — which is the whole point. A command that returned an error is already in front of the model; there is nothing invisible left to point out.

An assertion cannot refuse

The tool has already run. A deny stance therefore speaks exactly like advise, the same way it does at a session opening.

What an assertion can do is state a fact:

amont-agent/push-landed: `git push` exited 0, but origin/main is at d0765d4f9
while the local branch is at 8970c7ffb. The push did not land. Run the push
again on its own and read its output, then confirm with `git ls-remote`.

That is not advice to weigh. It is the remote's answer.

What it refuses to judge

push-landed handles the unambiguous shapes and nothing else. A HEAD:refs/heads/other refspec, a tag push, several refspecs at once, --delete, --mirror, --all: each needs a different question asked of the remote, and a confidently wrong accusation costs the channel its credibility — which is the only thing the channel has.

The same goes for everything it cannot establish: a detached HEAD, a remote given as a URL, a working directory that has gone, a remote that cannot be reached without a password. All silence.

It can never prompt

Hooks run with no controlling terminal, so a credential prompt does not fail — it hangs, and it hangs the session rather than this process. Every child runs with GIT_TERMINAL_PROMPT=0, GIT_ASKPASS/SSH_ASKPASS disabled, ssh in BatchMode, and a five-second deadline. A guard installed to make pushing safer must never be the reason a push becomes impossible.

Measuring

examine is pure, so the backtester replays it like any rule:

$ amont-agent backtest push-landed --since 2026-07-06
push-landed   1007   38.7   routine   observe

Read that number correctly. For a rule, a firing is a mistake caught. For an assertion, a firing is a question asked — 1,007 pushes in 29,758 Bash calls, about one call in twenty-six paying for one git ls-remote. It speaks only when the answer disagrees, which is far rarer.

How often a claim is actually broken is not backtestable at all: verify touches the world, and the world has moved since those commands ran. That number accumulates forward, in the journal:

$ grep push-landed ~/.claude/amont-agent/journal.log

held is a push that landed, broken one that did not, unverified one this crate declined to judge.