build: unify the gate so root make check covers the backend (closes #16)

Root `make check` only ever ran the frontend, so the "main is always
green" policy was satisfied vacuously: the Go backend could be entirely
broken and the root gate stayed green.

- The backend moves onto scripts-to-rule-them-all. Its test, lint, fmt,
  fmt-check, build, run and clean implementations now live in
  `backend/script/`, and `backend/Makefile` is thin shims. The backend
  is its own project (own module, README, LICENSE, linter config,
  Dockerfile stage), and `Dockerfile.backend` only copies `backend/`
  into its builder, so its scripts have to live under `backend/`.
- The root `script/test`, `script/lint`, `script/fmt` and
  `script/fmt-check` now run the frontend step and then the matching
  `backend/script/*` step, so `script/check` — and therefore the
  pre-commit hook — gates both halves. The frontend-only steps moved
  into `script/frontend-*` so nothing is duplicated.
- `script/bootstrap` now provisions the backend's toolchain as well,
  because widening the gate without widening bootstrap left the
  documented fresh-clone path (`make setup`) installing a pre-commit
  hook that rejected every commit with `golangci-lint: not found`. Go
  is reused when the installed version is new enough, otherwise it is
  installed from the official `go1.25.7` release archive; golangci-lint
  is installed at exactly `2.7.2`, the version `Dockerfile.backend`
  pins, so local findings match CI. Both come from a specific release
  archive whose sha256 is hardcoded here and verified before anything
  is unpacked — never an install script piped to a shell — and both are
  symlinked onto `PATH`, since nvm-style activation does not reach
  `make` or the git hook.
- `script/frontend-check` is the frontend half of the gate, exposed as
  the `frontend-check` target, for the frontend Dockerfile: its build
  stage is a node image with no Go toolchain. The backend half is gated
  by `Dockerfile.backend`, and `script/cibuild` builds both images, so
  the two Dockerfiles together still gate the whole repo. The
  `backend-check` target is the mirror of it. Both targets are named
  after the script they shim, like every other target.
- `script/cibuild` builds both images through one `build_image` helper,
  and the Gitea workflow's only build step is `script/cibuild`; the raw
  `docker build -f Dockerfile.backend .` is gone from the workflow.
  `script/docker` likewise builds and tags both images.
- `backend/Makefile`'s `hooks` target is removed. It wrote the same
  `.git/hooks/pre-commit` as `script/install-precommit`, so the two
  clobbered each other and the developer silently ended up gating on
  only one half of the repo. `script/install-precommit` is now the only
  installer, and the hook it writes runs the repo-wide `script/check`.
- `backend/Makefile`'s `docker` target is removed too: the backend image
  builds from the repo root with a root-level Dockerfile, so it belongs
  to the root `script/docker` and `script/cibuild` rather than to a
  backend script that would have to reach outside `backend/`.
- `backend/script/lint` verifies that `.golangci.yml` still matches its
  pinned sha256 before running the linter. Offline hash comparison, no
  network. The pin is marked provisional in the file: it is the config
  currently on `main`, and the comment names PR #31 and the canonical
  hash that must replace it when #31 lands.
- Every script locates the repo root with the mandated
  `$(cd "$(dirname "$0")/.." && pwd -P)` idiom, `cd`s there, and calls
  siblings as `"$ROOT/script/<name>"`; the `SCRIPT_DIR` variant is gone.

READMEs at the root and in `backend/` document every script, the
backend's Getting Started separates commands run from `backend/` from
those run at the repo root, and `TODO.md` records the change.

backend/Makefile

@@ -1,53 +1,38 @@
-UNAME_S := $(shell uname -s)
-VERSION := $(shell git describe --always --dirty)
-BUILDARCH := $(shell uname -m)
-BINARY := netwatch-server
+# Standard targets are thin shims; the implementations live in
+# backend/script/ per the scripts-to-rule-them-all pattern (see the
+# Entrypoints section of README.md).
+#
+# There is no `hooks` target here: the repo has exactly one pre-commit
+# hook installer, the root `script/install-precommit`, and the hook it
+# installs gates both halves of the repo. There is no `docker` target
+# either: the backend image is built from Dockerfile.backend with the
+# repo root as its context, so it belongs to the root `make docker` and
+# `script/cibuild`.
 
-GOLDFLAGS += -X main.Version=$(VERSION)
-GOLDFLAGS += -X main.Buildarch=$(BUILDARCH)
-
-ifeq ($(UNAME_S),Darwin)
-	GOFLAGS := -ldflags "$(GOLDFLAGS)"
-else
-	GOFLAGS = -ldflags "-linkmode external -extldflags -static $(GOLDFLAGS)"
-endif
-
-.PHONY: all build test lint fmt fmt-check check docker hooks run clean
+.PHONY: all build test lint fmt fmt-check check run clean
 
 all: build
 
-build: ./$(BINARY)
-
-./$(BINARY): $(shell find . -name '*.go' -type f) go.mod go.sum
-	go build -o $@ $(GOFLAGS) ./cmd/netwatch-server/
+build:
+	@script/build
 
 test:
-	timeout 30 go test ./...
+	@script/test
 
 lint:
-	golangci-lint run ./...
+	@script/lint
 
 fmt:
-	go fmt ./...
+	@script/fmt
 
 fmt-check:
-	@test -z "$$(gofmt -l .)" || \
-		(echo "Files not formatted:"; gofmt -l .; exit 1)
+	@script/fmt-check
 
-check: test lint fmt-check
+check:
+	@script/check
 
-docker:
-	timeout 300 docker build -t netwatch-server -f ../Dockerfile.backend ..
-
-hooks:
-	@printf '#!/bin/sh\ncd backend && make check\n' > \
-		$$(git rev-parse --show-toplevel)/.git/hooks/pre-commit
-	@chmod +x \
-		$$(git rev-parse --show-toplevel)/.git/hooks/pre-commit
-	@echo "Pre-commit hook installed"
-
-run: build
-	./$(BINARY)
+run:
+	@script/run
 
 clean:
-	rm -f ./$(BINARY)
+	@script/clean

backend/README.md

@@ -4,18 +4,54 @@ SPA and persists them as zstd-compressed JSONL files on disk.
 
 ## Getting Started
 
+From this directory (`backend/`):
+
 ```bash
 # Build and run locally
 make run
 
-# Run tests, lint, and format check
+# Run the backend's tests, lint, and format check
 make check
+```
 
-# Docker
-docker build -t netwatch-server .
+From the repo root, one directory up — `Dockerfile.backend` lives there and its
+build context is the repo root, so there is no `docker` target here:
+
+```bash
+# Build both images, including netwatch-server
+make docker
+
+# Run the backend image
 docker run -p 8080:8080 netwatch-server
 ```
 
+## Entrypoints
+
+This project follows the same
+[Scripts to Rule Them All](https://github.com/github/scripts-to-rule-them-all)
+pattern as the repo root: the implementations live in `backend/script/` and the
+targets in `backend/Makefile` are thin shims that call them. The repo root's
+`script/test`, `script/lint`, `script/fmt` and `script/fmt-check` call these
+too, so the root `make check` covers the backend.
+
+- `script/build` — compile `netwatch-server` with the version and architecture
+  stamped in via ldflags (statically linked on Linux)
+- `script/test` — run the Go tests under a 30-second timeout
+- `script/lint` — assert `.golangci.yml` still matches its pinned sha256, then
+  run golangci-lint
+- `script/fmt` — format the Go sources (writes)
+- `script/fmt-check` — check Go formatting (read-only)
+- `script/check` — run test, lint, and fmt-check
+- `script/run` — build and run the server locally
+- `script/clean` — remove build artifacts
+
+There is deliberately no `hooks` target here: the repo has exactly one
+pre-commit hook installer, the root `script/install-precommit`, and the hook it
+installs runs the root `script/check`, which gates both halves of the repo.
+There is no `docker` target either: `Dockerfile.backend` lives at the repo root
+and builds with the repo root as its context, so the backend image is built by
+the root `make docker` and by `script/cibuild`.
+
 ## Rationale
 
 The NetWatch frontend collects latency measurements from the browser but has no

backend/script/build

@@ -0,0 +1,27 @@
+#!/bin/sh
+# script/build: compile the netwatch-server binary into the backend
+# project root. Version and architecture are stamped into the binary via
+# ldflags; on Linux the binary is statically linked.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+BINARY="netwatch-server"
+
+main() {
+    cd "$ROOT"
+
+    # git describe fails outside a working repo (e.g. a source tarball),
+    # which must not abort the build.
+    version="$(git describe --always --dirty 2>/dev/null || echo unknown)"
+    buildarch="$(uname -m)"
+
+    ldflags="-X main.Version=$version -X main.Buildarch=$buildarch"
+    if [ "$(uname -s)" != "Darwin" ]; then
+        ldflags="-linkmode external -extldflags -static $ldflags"
+    fi
+
+    go build -o "$BINARY" -ldflags "$ldflags" ./cmd/netwatch-server/
+}
+
+main "$@"

backend/script/check

@@ -0,0 +1,16 @@
+#!/bin/sh
+# script/check: run all backend checks (test, lint, fmt-check). Must not
+# modify any files. The root script/check calls this, so the repo-wide
+# gate covers the backend.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    "$ROOT/script/test"
+    "$ROOT/script/lint"
+    "$ROOT/script/fmt-check"
+}
+
+main "$@"

backend/script/clean

@@ -0,0 +1,12 @@
+#!/bin/sh
+# script/clean: remove build artifacts.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    rm -f netwatch-server
+}
+
+main "$@"

backend/script/fmt

@@ -0,0 +1,12 @@
+#!/bin/sh
+# script/fmt: format all Go sources in the backend (writes).
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    go fmt ./...
+}
+
+main "$@"

backend/script/fmt-check

@@ -0,0 +1,18 @@
+#!/bin/sh
+# script/fmt-check: check Go formatting (read-only). Same scope as
+# script/fmt, but fails instead of writing.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    unformatted="$(gofmt -l .)"
+    if [ -n "$unformatted" ]; then
+        echo "Files not formatted:"
+        echo "$unformatted"
+        exit 1
+    fi
+}
+
+main "$@"

backend/script/lint

@@ -0,0 +1,56 @@
+#!/bin/sh
+# script/lint: run the Go linter over the backend.
+#
+# .golangci.yml is standardized org-wide and must never be edited here
+# (REPO_POLICIES.md). Its last silent drift replaced the v2 schema with
+# v1 keys, which left every threshold in the file inert while the build
+# stayed green. This script therefore asserts the file still matches the
+# pinned copy byte for byte before the linter runs. The check is a local
+# hash comparison: no network, no remote schema, nothing unpinned in the
+# build path.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+# sha256 of the pinned backend/.golangci.yml.
+#
+# PROVISIONAL. The hash below is the file currently on main, which is
+# the schema-invalid v1-keyed config described above: it is pinned only
+# so this branch and main stay green, NOT because it is canonical.
+#
+# The canonical org-wide .golangci.yml is
+# 021cc83f4e6fc7c31b95b34b846723dfcf20b66b7baeea1dc40406e643346bcb,
+# and PR #31 replaces backend/.golangci.yml with it. When #31 lands,
+# GOLANGCI_CONFIG_SHA256 must be updated to that hash in the same
+# commit. Until then, do not treat the pinned file as the standard.
+GOLANGCI_CONFIG_SHA256="33ba2bf7fe4a44779d09b0fb31d6daf03685f8dc9d2bc417f963d7aabb0d17dc"
+
+# sha256 <file>: print the file's sha256, coreutils or Darwin/busybox.
+sha256() {
+    if command -v sha256sum >/dev/null 2>&1; then
+        sha256sum "$1" | cut -d' ' -f1
+    else
+        shasum -a 256 "$1" | cut -d' ' -f1
+    fi
+}
+
+check_config_hash() {
+    actual="$(sha256 .golangci.yml)"
+    if [ "$actual" != "$GOLANGCI_CONFIG_SHA256" ]; then
+        echo ".golangci.yml has drifted from the pinned config."
+        echo "  expected $GOLANGCI_CONFIG_SHA256"
+        echo "  actual   $actual"
+        echo "Restore it verbatim from sneak/prompts; do not edit it."
+        echo "Only update GOLANGCI_CONFIG_SHA256 in this script when the"
+        echo "pinned config is deliberately replaced with a new standard."
+        exit 1
+    fi
+}
+
+main() {
+    cd "$ROOT"
+    check_config_hash
+    golangci-lint run ./...
+}
+
+main "$@"

backend/script/run

@@ -0,0 +1,13 @@
+#!/bin/sh
+# script/run: build and run netwatch-server locally.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    "$ROOT/script/build"
+    exec ./netwatch-server "$@"
+}
+
+main "$@"

backend/script/test

@@ -0,0 +1,12 @@
+#!/bin/sh
+# script/test: run the backend test suite.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    timeout 30 go test ./...
+}
+
+main "$@"