main() is one call into internal/cli (closes #160)

cmd/netwatch-server/main.go parsed the command line, ran the check-cidr
and prepare-data-dir subcommands and built the fx application itself;
the Go style guide puts all of that in internal/ or pkg/. The new
package internal/cli does it, with the same arguments, messages and
exit codes. main() is now os.Exit(cli.Main(os.Stderr, Appname, Version,
os.Args[1:], cli.RunServer)): Main takes the writer for errors and the
function that runs the server, so its tests give it a buffer and a
function that fails them. Appname and Version stay in main, where the
build sets Version. The function behind prepare-data-dir also takes the
volume and the user's name, so its own tests give it a temporary
directory and the user they run as.

Model: opus-5-5

.gitea/workflows/check.yml

@@ -1,9 +1,20 @@
 name: check
 on: [push]
+# Free the shared runner: a new push cancels only the same branch's older run.
+concurrency:
+    group: ${{ github.workflow }}-${{ github.ref }}
+    cancel-in-progress: true
 jobs:
     check:
         runs-on: ubuntu-latest
+        # Free the shared runner from a hung build.
+        timeout-minutes: 20
         steps:
             # actions/checkout v4.2.2, 2026-02-22
             - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+              # script/cibuild needs no token, so none is left in .git/config.
+              with:
+                  persist-credentials: false
+                  # All history and tags, so git describe finds the version tag.
+                  fetch-depth: 0
             - run: script/cibuild

README.md

@@ -41,11 +41,13 @@ The scripts cover both the frontend and the Go backend, so `make check` fails if
 either one is broken. We provide:
 
 - `script/bootstrap` — install all dependencies (the pinned node via nvm unless
-  one new enough for the frontend's dependencies is installed, yarn via
-  corepack, `yarn install --frozen-lockfile`, Go `GO_VERSION` unless the `go` on
-  `PATH` is exactly that version, and the Go modules), linking what it installs
-  itself into `~/.local/bin`, which has to be on `PATH`. It installs no Go
-  linter and not Docker: `make test` and `make lint` run in Docker
+  the `node` on `PATH` has the pinned major version and is new enough for the
+  frontend's dependencies, yarn `YARN_VERSION` via corepack, or npm where there
+  is no corepack, unless the `yarn` on `PATH` is exactly that version,
+  `yarn install --frozen-lockfile`, Go `GO_VERSION` unless the `go` on `PATH` is
+  exactly that version, and the Go modules), linking what it installs itself
+  into `~/.local/bin`, which has to be on `PATH`. It installs no Go linter and
+  not Docker: `make test` and `make lint` run in Docker
 - `script/setup` — make a fresh clone ready for development: bootstrap plus the
   git pre-commit hook
 - `script/dev` — run the Vite dev server, which proxies `/api` to a locally
@@ -58,6 +60,12 @@ either one is broken. We provide:
   defaults (see [Settings](#settings))
 - `script/clean` — remove what `script/build` writes
 - `script/projectname` — print the project name (used for the Docker image tag)
+- `script/yarn` — run yarn with the given arguments under the node
+  `script/bootstrap` would use: with `~/.local/bin` first on `PATH`, the first
+  `node` on that `PATH` when it has the pinned major version and is new enough
+  for the frontend's dependencies, and otherwise the pinned node in nvm. Every
+  script that runs yarn on the host runs it through this one, except
+  `script/bootstrap`, which picks its own node and yarn
 - `script/test` — build the `test` phase of `Dockerfile`, writing no image: the
   frontend's unit tests in its `frontend-test` stage, and the backend's Go tests
   with the race detector and coverage. The frontend's production build is left

TODO.md

@@ -12,7 +12,8 @@
 pre-1.0. No git tags. `main` is the stable branch and `next` the development
 branch, which every PR targets. The frontend and the Go backend ship as one
 Docker image, and the Gitea workflow `.gitea/workflows/check.yml` runs
-`script/cibuild` on every push. Working toward 1.0.0.
+`script/cibuild` on every push, and cancels the older run on the same branch.
+Working toward 1.0.0.
 
 # Next Step
 
@@ -29,11 +30,41 @@ Run `make frontend-viewport-test` in CI as its own step; it is not part of
   `Appname` and `Version` stay in `main`, where the build sets `Version`, and
   `main` gives `cli.Main` stderr and the function that runs the server, which
   the tests replace with a buffer and a function that fails them. Unit tests
-  call `cli.Main` with `check-cidr` and a CIDR it takes and one it refuses, and
-  check the exit code, and with `prepare-data-dir` and a path outside `/data`,
-  and check that it exits 1 with the error from looking up the `netwatch` user,
-  which the test image does not have. Others give each subcommand input it takes
-  and input it refuses, and check the exit code and what it writes to stderr
+  call `cli.Main` with `check-cidr` and a CIDR the server takes and one it
+  refuses, and check the exit code and what it writes to stderr, and with
+  `prepare-data-dir` and a path outside `/data`, and check that it exits 1 with
+  the error from looking up the `netwatch` user, which the test image does not
+  have. Others give the functions behind the subcommands input they take and
+  input they refuse, and check the exit code and what they write to stderr
+- 2026-10-19: `.gitea/workflows/check.yml` is the sneak/prompts copy at
+  `0653579` ([#153](https://git.eeqj.de/sneak/netwatch/issues/153)). Its
+  checkout step sets `fetch-depth: 0`, so CI clones all history and tags, and
+  `git describe` in `script/cibuild` gives the image built from a tagged commit
+  the tag as its version; it gave the short commit. The checkout step also sets
+  `persist-credentials: false`, so the job's token is not left in `.git/config`.
+  A new push cancels the older run on the same branch, and a run stops after 20
+  minutes
+- 2026-10-19: `script/bootstrap` keeps the `yarn` on `PATH` only when
+  `yarn --version` is exactly `YARN_VERSION`, and otherwise installs that
+  version as it did when no yarn was installed
+  ([#154](https://git.eeqj.de/sneak/netwatch/issues/154)); any yarn used to be
+  kept. It uses the `node` on `PATH` only when that node has the major version
+  of `NODE_VERSION`, as `REPO_POLICIES.md` asks, and is at least
+  `NODE_MIN_VERSION`; a node 24 was kept before. After installing node or yarn
+  it looks the tool up through `PATH` again and stops if that one fails the same
+  check, as it does for Go, and it prints the node and yarn versions it uses.
+  Every script that runs yarn on the host, except `script/bootstrap`, which
+  picks its own node and yarn, runs it through the new `script/yarn`. That
+  script puts `~/.local/bin` first on `PATH`, uses the first `node` on that
+  `PATH` when it passes the same test, and otherwise runs yarn under the pinned
+  node in nvm; `make build` ran yarn under whatever node was first on `PATH`
+- 2026-10-19: `bin/entrypoint.sh` has each of its steps in a function, and a
+  `main` at the end calls them in order, as the shell section of the code style
+  guide asks ([#163](https://git.eeqj.de/sneak/netwatch/issues/163)). It is
+  still POSIX sh with no `set -e`, and does what it did, with the same messages
+  and exit codes. Checked by running the image with each script: a normal start,
+  bad `PORT`, `TRUSTED_PROXIES` and `DATA_DIR` values, `docker stop`, INT, and
+  nginx exiting on its own
 - 2026-10-19: while report files cannot be written, the health check answers 503
   with `"status":"error"` and the same fields, so the image's `HEALTHCHECK`
   reports the container `unhealthy`

bin/entrypoint.sh

@@ -13,24 +13,27 @@ set -u
 # address and start anyway, and reports a bad port without naming
 # PORT, so a value that is not a usable port stops the container here,
 # before either process starts.
-export PORT="${PORT:-8080}"
-case "$PORT" in
-    *[!0-9]*)
-        echo "entrypoint: PORT must be a port number, not '$PORT'" >&2
+check_port() {
+    export PORT="${PORT:-8080}"
+    case "$PORT" in
+        *[!0-9]*)
+            echo "entrypoint: PORT must be a port number, not '$PORT'" >&2
+            exit 1
+            ;;
+    esac
+    # The length is checked first because, for a number too big for it,
+    # the shell's test prints an error and is false, so the range checks
+    # alone would let it through.
+    if [ "${#PORT}" -gt 5 ] || [ "$PORT" -lt 1 ] || [ "$PORT" -gt 65535 ]; then
+        echo "entrypoint: PORT must be from 1 to 65535, not '$PORT'" >&2
         exit 1
-        ;;
-esac
-# The length is checked first because, for a number too big for it,
-# the shell's test prints an error and is false, so the range checks
-# alone would let it through.
-if [ "${#PORT}" -gt 5 ] || [ "$PORT" -lt 1 ] || [ "$PORT" -gt 65535 ]; then
-    echo "entrypoint: PORT must be from 1 to 65535, not '$PORT'" >&2
-    exit 1
-fi
-if [ "$PORT" -eq 8081 ]; then
-    echo "entrypoint: PORT cannot be 8081, netwatch-server listens there" >&2
-    exit 1
-fi
+    fi
+    if [ "$PORT" -eq 8081 ]; then
+        echo "entrypoint: PORT cannot be 8081, netwatch-server" \
+            "listens there" >&2
+        exit 1
+    fi
+}
 
 # TRUSTED_PROXIES names the reverse proxies in front of the container,
 # as IP addresses or CIDRs separated by commas. nginx takes the client
@@ -47,21 +50,23 @@ fi
 # TRUSTED_PROXIES. Its error, naming the CIDR, is dropped for the one
 # below, naming the entry as written. set -f keeps a * in an entry from
 # becoming a list of file names.
-TRUSTED_PROXIES="${TRUSTED_PROXIES-10.0.0.0/8,172.16.0.0/12,192.168.0.0/16}"
-set -f
-for proxy in $(printf '%s' "$TRUSTED_PROXIES" | tr ',' ' '); do
-    case "$proxy" in
-        */*) cidr="$proxy" ;;
-        *:*) cidr="$proxy/128" ;;
-        *) cidr="$proxy/32" ;;
-    esac
-    if ! netwatch-server check-cidr "$cidr" 2> /dev/null; then
-        echo "entrypoint: TRUSTED_PROXIES must be IP addresses or CIDRs" \
-            "separated by commas; '$proxy' is neither" >&2
-        exit 1
-    fi
-    echo "set_real_ip_from $cidr;"
-done > /etc/nginx/trusted-proxies.conf
+write_trusted_proxies() {
+    TRUSTED_PROXIES="${TRUSTED_PROXIES-10.0.0.0/8,172.16.0.0/12,192.168.0.0/16}"
+    set -f
+    for proxy in $(printf '%s' "$TRUSTED_PROXIES" | tr ',' ' '); do
+        case "$proxy" in
+            */*) cidr="$proxy" ;;
+            *:*) cidr="$proxy/128" ;;
+            *) cidr="$proxy/32" ;;
+        esac
+        if ! netwatch-server check-cidr "$cidr" 2> /dev/null; then
+            echo "entrypoint: TRUSTED_PROXIES must be IP addresses or CIDRs" \
+                "separated by commas; '$proxy' is neither" >&2
+            exit 1
+        fi
+        echo "set_real_ip_from $cidr;"
+    done > /etc/nginx/trusted-proxies.conf
+}
 
 # netwatch-server keeps its report files in DATA_DIR, on the /data
 # volume, which may be a host directory owned by root or by another
@@ -73,12 +78,10 @@ done > /etc/nginx/trusted-proxies.conf
 # naming DATA_DIR, unless DATA_DIR is /data or a path below it, and it
 # acts on nothing outside /data, whatever symbolic or hard links it
 # meets there.
-export DATA_DIR="${DATA_DIR:-/data/reports}"
-netwatch-server prepare-data-dir "$DATA_DIR" || exit 1
-
-# A stop signal is only noted here; the loop below acts on it.
-stop_requested=""
-trap 'stop_requested=yes' TERM INT
+prepare_data_dir() {
+    export DATA_DIR="${DATA_DIR:-/data/reports}"
+    netwatch-server prepare-data-dir "$DATA_DIR" || exit 1
+}
 
 # netwatch-server runs as the netwatch user and listens on loopback
 # only, on a port other than the public one; configs/nginx.conf proxies
@@ -87,9 +90,11 @@ trap 'stop_requested=yes' TERM INT
 # the container has. The netwatch user has no login shell, hence -s
 # /bin/sh. busybox su replaces itself with the command instead of
 # staying on as its parent, so $! is the server's own PID.
-BIND_ADDRESS=127.0.0.1 PORT=8081 TRUSTED_PROXIES=127.0.0.1/32 \
-    su -s /bin/sh netwatch -c 'exec netwatch-server' &
-backend=$!
+start_backend() {
+    BIND_ADDRESS=127.0.0.1 PORT=8081 TRUSTED_PROXIES=127.0.0.1/32 \
+        su -s /bin/sh netwatch -c 'exec netwatch-server' &
+    backend=$!
+}
 
 # nginx starts through the nginx image's own entrypoint, which applies
 # the image's start-up configuration and then replaces itself with
@@ -98,9 +103,11 @@ backend=$!
 # that rendering to PORT: a variable nginx itself uses, such as $uri,
 # would otherwise be replaced by an environment variable of the same
 # name.
-NGINX_ENVSUBST_FILTER='^PORT$' \
-    /docker-entrypoint.sh nginx -g 'daemon off;' &
-nginx=$!
+start_nginx() {
+    NGINX_ENVSUBST_FILTER='^PORT$' \
+        /docker-entrypoint.sh nginx -g 'daemon off;' &
+    nginx=$!
+}
 
 running() {
     kill -0 "$1" 2>/dev/null
@@ -109,26 +116,47 @@ running() {
 # POSIX sh cannot wait for whichever of two children exits first, so
 # look once a second. The shell collects a child that has exited while
 # it runs sleep, and running() is false for that child from then on.
-while [ -z "$stop_requested" ] && running "$backend" && running "$nginx"; do
-    sleep 1
-done
+wait_for_stop_or_exit() {
+    while [ -z "$stop_requested" ] && running "$backend" && running "$nginx"; do
+        sleep 1
+    done
+}
 
 # Stop both, then wait until neither is left.
-kill -TERM "$backend" "$nginx" 2>/dev/null
-while running "$backend" || running "$nginx"; do
-    sleep 1
-done
-
-wait "$backend"
-backend_status=$?
-wait "$nginx"
-nginx_status=$?
-echo "entrypoint: netwatch-server exited $backend_status," \
-    "nginx exited $nginx_status"
+stop_both() {
+    kill -TERM "$backend" "$nginx" 2>/dev/null
+    while running "$backend" || running "$nginx"; do
+        sleep 1
+    done
+}
 
 # Success is a requested stop that both processes exited cleanly from.
-if [ -n "$stop_requested" ] && [ "$backend_status" -eq 0 ] &&
-    [ "$nginx_status" -eq 0 ]; then
-    exit 0
-fi
-exit 1
+exit_with_status() {
+    wait "$backend"
+    backend_status=$?
+    wait "$nginx"
+    nginx_status=$?
+    echo "entrypoint: netwatch-server exited $backend_status," \
+        "nginx exited $nginx_status"
+    if [ -n "$stop_requested" ] && [ "$backend_status" -eq 0 ] &&
+        [ "$nginx_status" -eq 0 ]; then
+        exit 0
+    fi
+    exit 1
+}
+
+main() {
+    check_port
+    write_trusted_proxies
+    prepare_data_dir
+    # A stop signal is only noted here; wait_for_stop_or_exit acts on it.
+    stop_requested=""
+    trap 'stop_requested=yes' TERM INT
+    start_backend
+    start_nginx
+    wait_for_stop_or_exit
+    stop_both
+    exit_with_status
+}
+
+main "$@"

internal/cli/cli.go

@@ -29,9 +29,9 @@ import (
 // with appname and version, the name and version the server logs and
 // reports. main passes os.Stderr and RunServer; the tests pass a
 // buffer and a function that fails them, so that no test starts the
-// server. When serve is RunServer and the server fails to start or to
-// stop, fx's Run exits the process with status 1 and Main never
-// returns.
+// server. When serve is RunServer and the server fails to start, to
+// listen or to stop, fx's Run exits the process with status 1 and Main
+// never returns.
 func Main(
 	stderr io.Writer,
 	appname, version string,
@@ -96,8 +96,8 @@ func prepareDataDir(stderr io.Writer, volume, dataDir, username string) int {
 
 // RunServer runs the server until it is told to stop, with appname and
 // version as the name and version it logs and reports. If the server
-// fails to start or to stop, fx's Run exits the process with status 1
-// itself.
+// fails to start, to listen or to stop, fx's Run exits the process
+// with status 1 itself.
 func RunServer(appname, version string) {
 	globals.Appname = appname
 	globals.Version = version

internal/cli/cli_test.go

@@ -2,7 +2,6 @@ package cli_test
 
 import (
 	"bytes"
-	"io"
 	"os"
 	"os/user"
 	"path/filepath"
@@ -14,18 +13,31 @@ import (
 	"sneak.berlin/go/netwatch/internal/reportbuf"
 )
 
-// TestMainRunsCheckCIDR: Main given check-cidr returns 0 for a CIDR the
-// server takes in its TRUSTED_PROXIES and 1 for one it refuses, and
-// does not start the server.
+// TestMainRunsCheckCIDR: Main given check-cidr returns 0, writing
+// nothing, for a CIDR the server takes in its TRUSTED_PROXIES, and 1,
+// with an error naming TRUSTED_PROXIES and the CIDR, for one it
+// refuses, and does not start the server.
 func TestMainRunsCheckCIDR(t *testing.T) {
 	t.Parallel()
 
-	for cidr, want := range map[string]int{"10.0.0.0/8": 0, "1.2.3/32": 1} {
-		code := cli.Main(io.Discard, "netwatch", "test",
-			[]string{"check-cidr", cidr}, failIfServerStarts(t))
-		if code != want {
-			t.Errorf("check-cidr %q: exit %d, want %d", cidr, code, want)
-		}
+	var stderr bytes.Buffer
+
+	code := cli.Main(&stderr, "netwatch", "test",
+		[]string{"check-cidr", "10.0.0.0/8"}, failIfServerStarts(t))
+	if code != 0 || stderr.Len() != 0 {
+		t.Errorf("check-cidr 10.0.0.0/8: exit %d, stderr %q; want exit 0 and no output",
+			code, stderr.String())
+	}
+
+	stderr.Reset()
+
+	code = cli.Main(&stderr, "netwatch", "test",
+		[]string{"check-cidr", "1.2.3/32"}, failIfServerStarts(t))
+
+	want := `TRUSTED_PROXIES "1.2.3/32": `
+	if code != 1 || !strings.HasPrefix(stderr.String(), want) {
+		t.Errorf("check-cidr 1.2.3/32: exit %d, stderr %q; want exit 1 and %q...",
+			code, stderr.String(), want)
 	}
 }
 

script/add-dependency

@@ -23,8 +23,8 @@ main() {
     "" | -* | *[[:space:]]*) usage ;;
     esac
     cd "$ROOT"
-    yarn add --dev "$1"
-    yarn install --frozen-lockfile
+    "$ROOT/script/yarn" add --dev "$1"
+    "$ROOT/script/yarn" install --frozen-lockfile
 }
 
 main "$@"

script/bootstrap

@@ -3,11 +3,14 @@
 # this repo. Idempotent: every install is guarded by a check so already
 # installed tools are skipped. Base tooling comes from nix, apt, brew,
 # or apk (detected in that order); assumes nothing is present. Node is
-# used directly if it is at least NODE_MIN_VERSION; otherwise it is
-# installed at a pinned version via nvm (installing nvm itself first,
-# from a hash-verified release archive, never curl | sh). Go, with its
-# gofmt, is used directly only if it is exactly GO_VERSION; otherwise
-# that release is installed from its hash-verified archive.
+# used directly only if it has the major version of NODE_VERSION and is
+# at least NODE_MIN_VERSION; otherwise NODE_VERSION is installed via nvm
+# (installing nvm itself first, from a hash-verified release archive,
+# never curl | sh). Yarn is used directly only if it is exactly
+# YARN_VERSION; otherwise that version is prepared through corepack,
+# or installed with npm where there is no corepack.
+# Go, with its gofmt, is used directly only if it is exactly GO_VERSION;
+# otherwise that release is installed from its hash-verified archive.
 #
 # What this script installs outside the system package manager lives
 # under $HOME and is linked into ~/.local/bin, where make and the git
@@ -142,32 +145,63 @@ ensure_nvm() {
     rm -rf "$tmp"
 }
 
-# node_ok: the node on PATH is at least NODE_MIN_VERSION. node itself
-# compares the two: major, then minor, then patch.
+# node_ok: the node on PATH has the major version of NODE_VERSION and is
+# at least NODE_MIN_VERSION. Only the major is compared with the pin,
+# as REPO_POLICIES.md asks. node itself compares the versions: major,
+# then minor, then patch. A node that fails does not pass.
+# script/bootstrap and script/yarn carry this function unchanged.
 node_ok() {
-    if missing node; then return 1; fi
+    if ! command -v node >/dev/null 2>&1; then return 1; fi
     node -e '
         const have = process.versions.node.split(".").map(Number);
         const want = process.argv[1].split(".").map(Number);
+        const pinned = process.argv[2].split(".").map(Number);
+        if (have[0] !== pinned[0]) process.exit(1);
         for (let i = 0; i < 3; i++) {
             if (have[i] !== want[i]) process.exit(have[i] > want[i] ? 0 : 1);
         }
-    ' "$NODE_MIN_VERSION"
+    ' "$NODE_MIN_VERSION" "$NODE_VERSION"
 }
 
 # ensure_node: unless node_ok, install NODE_VERSION and link its node.
+# Afterwards node is looked up through PATH again and must pass node_ok.
 ensure_node() {
-    if node_ok; then return 0; fi
+    if node_ok; then
+        echo "bootstrap: using node $(node --version)"
+        return 0
+    fi
     ensure_nvm
     nvm_sh "nvm install $NODE_VERSION"
     link_bin "$HOME/.nvm/versions/node/v$NODE_VERSION/bin/node" node
+    hash -r
+    if ! node_ok; then
+        echo "bootstrap: after installing node $NODE_VERSION through nvm," >&2
+        echo "  the node on PATH, $(command -v node), is not it" >&2
+        exit 1
+    fi
+    echo "bootstrap: installed node $(node --version)"
 }
 
-# ensure_yarn: corepack writes its shims (pnpm and yarnpkg as well as
-# yarn) into $TOOLCHAIN rather than next to itself, and the npm fallback
-# installs there too; only yarn is linked.
+# yarn_ok: yarn --version on PATH prints exactly YARN_VERSION, compared
+# over the whole version. A yarn that fails or prints anything else does
+# not pass.
+yarn_ok() {
+    if missing yarn; then return 1; fi
+    version="$(yarn --version 2>/dev/null)" || return 1
+    [ "$version" = "$YARN_VERSION" ]
+}
+
+# ensure_yarn: unless yarn_ok, prepare YARN_VERSION and link its yarn.
+# corepack writes its shims (pnpm and yarnpkg as well as yarn) into
+# $TOOLCHAIN rather than next to itself, and the npm fallback installs
+# there too; only yarn is linked. Afterwards yarn is looked up through
+# PATH again and must pass yarn_ok, so another yarn that hides the link
+# stops bootstrap.
 ensure_yarn() {
-    if ! missing yarn; then return 0; fi
+    if yarn_ok; then
+        echo "bootstrap: using yarn $(yarn --version)"
+        return 0
+    fi
     shims="$TOOLCHAIN/corepack-shims"
     mkdir -p "$shims"
     if ! missing corepack; then
@@ -182,6 +216,13 @@ ensure_yarn() {
         shims="$TOOLCHAIN/npm-global/bin"
     fi
     link_bin "$shims/yarn" yarn
+    hash -r
+    if ! yarn_ok; then
+        echo "bootstrap: after installing yarn $YARN_VERSION in $shims," >&2
+        echo "  the yarn on PATH, $(command -v yarn), does not report it" >&2
+        exit 1
+    fi
+    echo "bootstrap: installed yarn $(yarn --version)"
 }
 
 # go_ok: the go on PATH has its gofmt beside it (a Go release ships the

script/build

@@ -8,7 +8,7 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    yarn build
+    "$ROOT/script/yarn" build
 
     # VERSION comes from the environment. Unset or empty, it is git
     # describe, or "dev" where there is no git or no repository history.

script/dev

@@ -7,7 +7,7 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    yarn dev
+    "$ROOT/script/yarn" dev
 }
 
 main "$@"

script/frontend-fmt

@@ -10,7 +10,7 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    yarn prettier --write '**/*.{js,css,html,md}'
+    "$ROOT/script/yarn" prettier --write '**/*.{js,css,html,md}'
 }
 
 main "$@"

script/frontend-fmt-check

@@ -7,7 +7,7 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    yarn prettier --check '**/*.{js,css,html,md}'
+    "$ROOT/script/yarn" prettier --check '**/*.{js,css,html,md}'
 }
 
 main "$@"

script/frontend-test

@@ -14,12 +14,14 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    NODE_OPTIONS=--test-reporter=dot timeout 90 yarn --silent run test || {
+    NODE_OPTIONS=--test-reporter=dot \
+        timeout 90 "$ROOT/script/yarn" --silent run test || {
         echo "--- Rerunning with every test listed for details ---"
-        NODE_OPTIONS=--test-reporter=spec timeout 90 yarn --silent run test
+        NODE_OPTIONS=--test-reporter=spec \
+            timeout 90 "$ROOT/script/yarn" --silent run test
         exit 1
     }
-    timeout 30 yarn build
+    timeout 30 "$ROOT/script/yarn" build
 }
 
 main "$@"

script/yarn

@@ -0,0 +1,55 @@
+#!/bin/sh
+# script/yarn: run yarn with the given arguments under the node
+# script/bootstrap would use. Every script that runs yarn on the host
+# runs it through this one, except script/bootstrap, which picks its
+# own node and yarn.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+# Must match the pins in script/bootstrap.
+NODE_VERSION="22.17.0"
+NODE_MIN_VERSION="22.13.0"
+
+# node_ok: the node on PATH has the major version of NODE_VERSION and is
+# at least NODE_MIN_VERSION. Only the major is compared with the pin,
+# as REPO_POLICIES.md asks. node itself compares the versions: major,
+# then minor, then patch. A node that fails does not pass.
+# script/bootstrap and script/yarn carry this function unchanged.
+node_ok() {
+    if ! command -v node >/dev/null 2>&1; then return 1; fi
+    node -e '
+        const have = process.versions.node.split(".").map(Number);
+        const want = process.argv[1].split(".").map(Number);
+        const pinned = process.argv[2].split(".").map(Number);
+        if (have[0] !== pinned[0]) process.exit(1);
+        for (let i = 0; i < 3; i++) {
+            if (have[i] !== want[i]) process.exit(have[i] > want[i] ? 0 : 1);
+        }
+    ' "$NODE_MIN_VERSION" "$NODE_VERSION"
+}
+
+# Run the yarn script/bootstrap installed: the yarn on PATH when the
+# node on PATH passes node_ok, and otherwise yarn under the pinned node
+# in nvm. nvm is a bash script, hence the subshell.
+run_yarn() {
+    if node_ok && command -v yarn >/dev/null 2>&1; then
+        exec yarn "$@"
+    fi
+    if node_ok || [ ! -s "$HOME/.nvm/nvm.sh" ]; then
+        echo "script/yarn: no yarn; run script/bootstrap first" >&2
+        exit 1
+    fi
+    exec bash -c '. "$HOME/.nvm/nvm.sh" && nvm use "$1" >/dev/null &&
+        shift && exec yarn "$@"' bash "$NODE_VERSION" "$@"
+}
+
+main() {
+    cd "$ROOT"
+    # script/bootstrap links the node and yarn it installs into
+    # ~/.local/bin, which the shell that called it may not have on PATH.
+    PATH="$HOME/.local/bin:$PATH"
+    run_yarn "$@"
+}
+
+main "$@"