Privacy-Period-Tracker/docs/architecture/githooks

Git hooks

Status: Current
Owner: _null
Last reviewed: 2026-08-18
Governs: .githooks/ — what runs before and after a commit
Review trigger: A new guard the repository wants run before a commit; any change
                to what a commit message must contain; any change to which
                Gradle tasks pre-commit runs

Three hooks, and the reason they live in the repository rather than in .git/hooks: that directory is not versioned, so a hook living there protects exactly one clone on exactly one machine.

The hooks are in .githooks/, and only there

The template this repository adopted keeps a master copy under docs/architecture/githooks/ and installs copies into .githooks/. Period does not, deliberately: pre-commit here is adapted for Gradle rather than npm, so a second copy would be a second version of a file somebody edits once and forgets — the exact failure ../../DOC_TRUST_MAP.md exists to prevent.

So .githooks/ holds the hooks and this document describes them. One copy of the code, one copy of the explanation.

Install

git config core.hooksPath .githooks

That is the whole setup, and it is per clone — every checkout runs it once, including a fresh clone on the same machine. An uninstalled hook fails silently, which is the same class of problem the hooks exist to prevent.

What each one does

Hook	Guard
pre-commit	the staged-diff secret scan; then :domain:cycle:test and :domain:prediction:test when .kt/.kts or a build file is staged; then scripts/schema-guard.sh when a Room entity or the schema export is staged
commit-msg	refuses a message with no conventional type — the closed vocabulary is in the hook's own header
post-commit	pushes to origin, so a guarded commit does not sit unpushed

Two things worth knowing before you rely on them

pre-commit does not compile the Android modules. It runs the two pure-JVM suites, which need no SDK and take about a second. Compiling :app needs the Android SDK and half a minute, and a hook people reach for --no-verify to avoid is worse than one that checks less. ./gradlew assembleRelease belongs to ../../security/SECURITY_CHECKLIST.md, which is where it is.

The suite it does run is not an arbitrary subset: it is the prediction acceptance cases from ../../planning/PRODUCT_PLAN.md §51, which guard the one claim this product is built on.

The schema guard is here rather than in the suite for a reason worth knowing. Room rewrites the schema export during compilation, so by the time any test runs, both sides of any in-process comparison describe the changed entity and agree. Only git can see that an already-committed schema file changed, and only a hook can ask git before the commit exists. scripts/schema-guard.sh carries the proof in its header — the check it replaced was watched staying green over exactly the failure it claimed to catch.

It exits 2 for "nothing was checked", and the hook treats 2 as a refusal. A missing schema directory is not a clean schema.

The secret scan's 2 is handled differently, and deliberately. A commit that only deletes files gives it nothing to scan, which is the right answer rather than a fault — so the hook accepts a 2 when the staged diff adds no lines, and refuses it whenever the diff adds any. Before that distinction existed, git rm was impossible and the refusal claimed a credential had been found.

post-commit pushes. That is the intent — the commit that first added a pre-commit hook to the project this came from sat unpushed for a day, guarded and invisible — but it is a surprise if you were not expecting it. It never forces, stays out of the way mid-rebase, and SKIP_PUSH=1 opts out loudly.

It has a second consequence worth knowing about: the push is what the Command Center reads, so whatever documentation was not in that commit is now behind the code by one push. That is the mechanical reason ../../WORK_CYCLE.md asks for doc edits in the same commit as the change rather than in a tidy-up afterwards — with this hook installed, "I will document it next commit" means the site has already published the version without it.

Escape hatches, and why they are loud

SKIP_GUARDS=1 git commit ...    # skips the scan and the tests, and says so
SKIP_PUSH=1   git commit ...    # commits without publishing, and says so
git commit --no-verify ...      # skips the hooks entirely, silently

Prefer the first two. They leave a line in the terminal saying the guard did not run, which is the difference between a deliberate exception and a habit.

Why a hook and not CI

Both, eventually. These are the guards that must run before the artifact exists: a check that fires after a push, or after a Play upload, catches the problem once it is already somewhere it cannot be taken back from. CI is the second opinion; this is the one that runs first.