.github/workflows/ci.yml

@@ -26,21 +26,7 @@ jobs:
         # The file list is printed so under-coverage shows up in the log, and
         # the comm below turns under-coverage into a failure rather than a
         # thing someone has to notice: every tracked `.sh` must be in the set.
-        #
-        # Install shellcheck when missing (#144). rig's default Forgejo label
-        # maps ubuntu-latest to catthehacker's act-22.04 (slim), which does not
-        # ship shellcheck; GitHub-hosted ubuntu-latest does. The conditional
-        # keeps each forge from paying for the other.
-        #
-        # sudo: load-bearing on GitHub (job runs as `runner` with passwordless
-        # sudo) and a no-op on act-22.04 (jobs run as uid 0; the image has no
-        # `runner` account). Do not delete it as "dead weight" — that breaks
-        # the GitHub half the day that image stops preinstalling shellcheck.
         run: |
-          if ! command -v shellcheck >/dev/null 2>&1; then
-            sudo apt-get update
-            sudo apt-get install -y shellcheck
-          fi
           shopt -s globstar dotglob
           files=(bin/* **/*.sh)
           printf 'shellcheck: %s\n' "${files[@]}"

changelog.d/139.md

@@ -1,4 +1,3 @@
 ### Fixed
 
-- `rig forgejo-runner install`, `rig runner install`, `rig users apply` and `rig bootstrap <tenant>` refuse with a named remedy when root's `PATH` carries no `/usr/sbin`, instead of dying on `useradd: command not found` after prompting for a token (#139)
-- `rig users apply` no longer reports success having silently skipped the sudoers drop-in when `visudo` is off `PATH` (#139)
+- `rig forgejo-runner install`, `rig runner install` and `rig users apply` refuse with a named remedy when root's `PATH` carries no `/usr/sbin`, instead of dying on `useradd: command not found` after prompting for a token (#139)

changelog.d/144.md

@@ -1,8 +0,0 @@
-### Added
-
-- Default Forgejo runner labels include opt-in `ubuntu-latest-full` for the GitHub-parity image (#144)
-
-### Fixed
-
-- `ci.yml` installs `shellcheck` when the runner image lacks it, so Forgejo's slim `ubuntu-latest` can run `check` (#144)
-- Plain `rig forgejo-runner install` warns when recorded labels are a retired rig default, without nagging custom `--labels` (#144)

commands/bootstrap-tenant.sh

@@ -31,8 +31,6 @@ HERE="$(cd "$(dirname "$(readlink -f "${BASH_SOURCE[0]}")")" && pwd)"
 . "$HERE/lib/templates.sh"       # templates_resolve / template_parse_env / render_tenant_context
 # shellcheck source=SCRIPTDIR/lib/users-config.sh
 . "$HERE/lib/users-config.sh"    # read_role_marker / root_door_of
-# shellcheck source=SCRIPTDIR/lib/admin-path.sh
-. "$HERE/lib/admin-path.sh"      # require_admin_bins
 # shellcheck source=SCRIPTDIR/lib/sshd.sh
 . "$HERE/lib/sshd.sh"            # harden_sshd (the staging-box tenant)
 # shellcheck source=SCRIPTDIR/lib/manifest.sh
@@ -202,15 +200,6 @@ else
 fi
 
 [ "$(id -u)" -eq 0 ] || die "must run as root"
-# Root is not enough here either (#139). This mint adds the tenant user to the
-# docker group with `usermod` far below — AFTER installing docker and node,
-# which is what makes it the worst-placed of the four call sites: on a
-# PATH-shorn root it dies mid-convergence with a bare `usermod: command not
-# found`, having already changed the machine, rather than before touching it.
-#
-# Unconditional because the docker block below is unconditional — "every tenant
-# gets docker" is the stated rule there, so every tenant reaches the usermod.
-require_admin_bins usermod
 if [ -r /etc/os-release ]; then
   # Sourced in a subshell: os-release defines VERSION, NAME, ID, etc. —
   # sourcing it in the main shell silently clobbers same-named script vars.

commands/forgejo-runner-install.sh

@@ -33,32 +33,7 @@ die()  { printf 'rig-forgejo-runner: ERROR: %s\n' "$1" >&2; exit "${2:-1}"; }
 # on the box itself. No docker-in-docker: the guide this came from stacks a
 # privileged dind sidecar with a plaintext tcp://…:2375 daemon to isolate jobs
 # from a shared CI server, and inside a box that boundary is already paid for.
-#
-# WHY act-22.04 (slim) for ubuntu-latest, not full-22.04 — measured 2026-08-01
-# against ghcr manifests (#144):
-#   act-22.04:  ~0.55 GB compressed / ~2.2 GB on disk — no shellcheck
-#   full-22.04: ~18.67 GB compressed / ~54.5 GB on disk — has shellcheck 0.8.0
-# A normal box-class ci tenant cannot hold 54.5 GB (typical free space ~34 GB).
-# So ubuntu-latest stays slim, and workflows must not assume GitHub-image tools
-# (rig's own ci.yml installs shellcheck when missing). Operators who need the
-# full tool surface opt in with runs-on: ubuntu-latest-full — that label is
-# inert until matched, so boxes that never ask pay nothing.
-DEFAULT_LABELS='ubuntu-latest:docker://ghcr.io/catthehacker/ubuntu:act-22.04,ubuntu-latest-full:docker://ghcr.io/catthehacker/ubuntu:full-22.04,docker:docker://node:22-bookworm'
-
-# labels_are_a_retired_default <recorded>
-#
-# True when <recorded> is a past DEFAULT_LABELS value rig has shipped — the
-# only plain-converge case that should warn about re-registration (#144).
-# Custom operator maps (drill's Leg 3, any --labels) must return false so a
-# bare re-run stays quiet. One pattern per past default; add when the string
-# changes. Extracted and driven by test/cli.sh — a grep pin alone cannot prove
-# the match is exact.
-labels_are_a_retired_default() {
-  case "${1:-}" in
-    'ubuntu-latest:docker://ghcr.io/catthehacker/ubuntu:act-22.04,docker:docker://node:22-bookworm') return 0 ;;
-    *) return 1 ;;
-  esac
-}
+DEFAULT_LABELS='ubuntu-latest:docker://ghcr.io/catthehacker/ubuntu:act-22.04,docker:docker://node:22-bookworm'
 
 # fetch_and_verify_sha256 <asset-url> <file> <sumfile> <label>
 #
@@ -120,10 +95,8 @@ usage: rig forgejo-runner install --instance <url> [options]
                         time). Pin it for a deterministic, auditable install.
   --name <name>         runner name (default: this host's hostname)
   --labels <csv>        runner labels; replaces the default. The default maps
-                        ubuntu-latest (slim act image), ubuntu-latest-full
-                        (opt-in parity image), and docker onto containers so
-                        a workflow written for GitHub runs; full tools need
-                        runs-on: ubuntu-latest-full or an install step.
+                        ubuntu-latest and docker onto container images, so a
+                        workflow written for GitHub runs unchanged.
   --user <name>         unprivileged service user (default: the tenant user
                         `ci` when it exists, else forgejo-runner; created if
                         absent; never root)
@@ -234,14 +207,7 @@ fi
 # Root is not enough: the admin binaries must also be reachable (#139). This
 # sits beside the root check so identity and capability are asserted together,
 # and BEFORE any prompt or download — a token typed for a doomed run is waste.
-#
-# BOTH binaries this command goes on to call: useradd at the user-create below,
-# usermod at the docker-group add further down. Naming only the first would
-# still consume the token on a PATH that happened to resolve useradd but not
-# usermod — the same failure one step later, which is the shape #75 exists to
-# refuse (a sweep that covers most of its call sites is the hole the next bug
-# arrives through).
-require_admin_bins useradd usermod
+require_admin_bins useradd
 if [ -r /etc/os-release ]; then
   # Sourced in a subshell: os-release defines VERSION (e.g. "13 (trixie)"),
   # which would clobber this script's $VERSION.
@@ -448,29 +414,14 @@ install -d -m 0755 -o "$RUNNER_USER" -g "$RUNNER_GROUP" "$USER_HOME/.cache"
 if [ -e "$RUNNER_DIR/.runner" ]; then
   log "already registered; skipping registration"
   # Registration was skipped, so the labels on the instance are the ones it was
-  # registered with — NOT whatever this invocation was passed. Forgejo owns
-  # labels from registration time; a re-run never rewrites them.
-  #
-  # Two warn paths (#144):
-  #   EXPLICIT --labels that differs → operator asked and it was not applied.
-  #   Plain converge whose recorded labels match a known *retired* default →
-  #   rig's default map moved (e.g. added ubuntu-latest-full). Without this
-  #   the operator re-runs install, sees "already registered", and believes
-  #   they have the new default while Forgejo still holds the old set.
-  #
-  # Do NOT warn on every RECORDED != current default: that fires forever for
-  # any runner the operator deliberately gave custom --labels (drill's Leg 3
-  # registers drill:docker://node:22-bookworm). The old LABELS_EXPLICIT-only
-  # gate existed to avoid that noise; retired-default matching keeps the
-  # silence for intentional maps and still catches silent drift off a past
-  # rig default. Re-register only to pick up labels the old set never had —
-  # nothing matching the recorded set is broken by the map change alone.
-  if [ -r "$RUNNER_DIR/.rig-labels" ]; then
+  # registered with — NOT whatever this invocation was passed. Say so when the
+  # operator explicitly asked for different ones, rather than letting the
+  # request evaporate. Only when EXPLICIT: comparing the default against a
+  # runner registered with custom labels would warn on every plain converge.
+  if [ "$LABELS_EXPLICIT" -eq 1 ] && [ -r "$RUNNER_DIR/.rig-labels" ]; then
     RECORDED="$(cat "$RUNNER_DIR/.rig-labels")"
-    if [ "$LABELS_EXPLICIT" -eq 1 ] && [ "$RECORDED" != "$LABELS" ]; then
+    if [ "$RECORDED" != "$LABELS" ]; then
       warn "--labels was not applied: this runner is already registered, and Forgejo owns its labels from registration time. It still has: ${RECORDED}. Labels are what 'runs-on' matches, so changing them means re-registering: 'rig forgejo-runner remove' then install again with the labels you want."
-    elif [ "$LABELS_EXPLICIT" -eq 0 ] && labels_are_a_retired_default "$RECORDED"; then
-      warn "this runner was registered with an older rig default label set. The current default adds ubuntu-latest-full (the GitHub-parity image). Labels are fixed at registration, so picking it up means re-registering: 'rig forgejo-runner remove' then install again. Nothing you run today is affected — re-register only if you want the new label."
     fi
   fi
 else

commands/lib/admin-path.sh

@@ -10,24 +10,6 @@
 # versioned install root, emitted AFTER a registration token had been read off
 # the operator's terminal (#139).
 #
-# Which binaries this covers is measured, not assumed (Debian 13, 2026-08-01):
-#
-#   useradd usermod groupadd userdel groupdel   /usr/sbin   package: passwd
-#   visudo                                      /usr/sbin   package: sudo
-#   gpasswd                                     /usr/bin    package: passwd
-#
-# Two consequences worth keeping written down. `gpasswd` is in the same PACKAGE
-# as useradd but a different DIRECTORY, so it is reachable on a PATH-shorn root
-# and does not belong in any of these preflights — do not add it for symmetry.
-# And `visudo` shares the directory but not the package, so its absence has a
-# second, innocent cause (sudo simply not installed) that the others do not, so
-# `rig users apply` checks it separately, after the point where that cause is
-# ruled out. See the comment there.
-#
-# (Spelled without the `.sh` on purpose: test/cli.sh pins that exactly one file
-# under commands/ names that script, to catch a second caller appearing. A
-# comment is not a caller, but the pin is deliberately blunt and cheap.)
-#
 # It REFUSES rather than repairing PATH itself. A command that quietly prepends
 # /usr/sbin teaches the operator nothing and leaves a misconfigured host
 # misconfigured; the same reason bootstrap refuses rather than guessing. The

commands/users-apply.sh

@@ -141,7 +141,7 @@ done <<< "$PARSED"
 # Root is not enough: the admin binaries must also be reachable (#139). This
 # sits beside the root check so identity and capability are asserted together,
 # and BEFORE any prompt or download — a token typed for a doomed run is waste.
-require_admin_bins useradd usermod groupadd
+require_admin_bins useradd usermod
 
 # Identity management gates its INVOKER, not just its uid: %rig's sudoers rule
 # is binary-scoped but not argument-scoped, so without this gate a rig-role
@@ -201,26 +201,6 @@ if [ "$NEED_SUDO" -eq 1 ] && ! command -v sudo >/dev/null 2>&1; then
   DEBIAN_FRONTEND=noninteractive apt-get install -y -qq sudo
   CHANGED=1
 fi
-# visudo is checked HERE and not beside the root check, because until the block
-# above has run there is a legitimate reason for it to be absent: sudo is not
-# installed yet, and apply is what installs it. Above, a missing visudo would
-# be indistinguishable from that, so the refusal would fire on a healthy box.
-#
-# Below, it is unambiguous. sudo is present, so `visudo` missing means only one
-# thing: /usr/sbin is off PATH. And it MUST refuse here rather than be left to
-# the sudoers block further down, because that block asks `command -v visudo`
-# and treats false as "no sudo on the box means no role needed it" — which on a
-# PATH-shorn root is FALSE TWICE. A role does need it, sudo is installed, and
-# apply would finish reporting success having silently never written the
-# sudoers drop-in: the users get their roles and not the escalation the roles
-# are FOR. That is the failure this whole issue is about (a wrong effective
-# state reported as success, #12), in its quietest form — the other three sites
-# at least crash. Refusing before the first mutation is what keeps it loud.
-#
-# It sits before `groupadd` below, so nothing has been converged when it fires.
-if [ "$NEED_SUDO" -eq 1 ]; then
-  require_admin_bins visudo
-fi
 
 # --- groups ------------------------------------------------------------------
 groupadd -f rig-admin

test/cli.sh

@@ -3372,81 +3372,6 @@ check "preflight: the GitHub runner installer refuses too" 1 "useradd" \
   adm_run "$ROOT/commands/runner-install.sh" --repo o/r
 check "preflight: users apply refuses before it converges anything" 1 "useradd" \
   adm_run "$ROOT/commands/users-apply.sh" --file /dev/null
-
-# A sbin-less PATH loses ALL of /usr/sbin at once, so the checks above can only
-# ever prove the FIRST binary is named — `useradd` wins every race and would
-# hide a preflight that forgot the others. These fixtures resolve the earlier
-# binaries and withhold exactly one, which is the only way to show the sweep
-# covers what each command actually calls (the #75 lesson: a sweep that misses
-# one call site is how the next bug gets in).
-#
-# The withheld binary is real: these are PATHs, not stubs of the tools
-# themselves — a stub that silently succeeded would let convergence run on.
-admstub() {  # admstub <dir> <bin>... — a bindir resolving id(0) plus <bin>...
-  local d="$1"; shift
-  mkdir -p "$d"
-  # shellcheck disable=SC2016 # shell source being written, not expanded
-  printf '#!/usr/bin/env bash\nif [ "${1:-}" = -u ]; then printf "0\\n"; else exec /usr/bin/id "$@"; fi\n' > "$d/id"
-  chmod +x "$d/id"
-  local b
-  for b in "$@"; do printf '#!/usr/bin/env bash\nexit 0\n' > "$d/$b"; chmod +x "$d/$b"; done
-}
-adm_with() {  # adm_with <bindir> <cmd>...
-  local d="$1"; shift
-  env PATH="$d:/usr/local/bin:/usr/bin:/bin" "$@" 2>&1
-}
-# adm_saw <bindir> <pattern> <cmd>... — exit 0 if the run printed <pattern>.
-# Used with `check ... 1 ""` to assert a thing did NOT happen (a token prompt,
-# a group creation), the same shape as adm_prompted above.
-adm_saw() {
-  local d="$1" pat="$2"; shift 2
-  adm_with "$d" "$@" | grep -qi -- "$pat"
-}
-
-# useradd resolves, usermod does not — the forgejo installer calls both, and
-# only reaches usermod after the token has been spent.
-admstub "$ADMPATH_DIR/no-usermod" useradd
-check "preflight: forgejo-runner install names usermod when only useradd resolves" 1 "usermod" \
-  adm_with "$ADMPATH_DIR/no-usermod" "$ROOT/commands/forgejo-runner-install.sh" --instance https://f.example.com
-check "preflight: …and still refuses before the token prompt" 1 "" \
-  adm_saw "$ADMPATH_DIR/no-usermod" 'registration token:' \
-  "$ROOT/commands/forgejo-runner-install.sh" --instance https://f.example.com
-# users apply calls groupadd unconditionally, two lines into its convergence.
-admstub "$ADMPATH_DIR/no-groupadd" useradd usermod
-check "preflight: users apply names groupadd when useradd and usermod resolve" 1 "groupadd" \
-  adm_with "$ADMPATH_DIR/no-groupadd" "$ROOT/commands/users-apply.sh" --file /dev/null
-
-# visudo is the quiet one. With sudo INSTALLED and /usr/sbin off PATH, the
-# sudoers block reads `command -v visudo` as "no sudo on the box" and skips the
-# drop-in — apply then reports success having granted roles without the
-# escalation those roles exist for. So this fixture needs a role that wants
-# sudo, and asserts the refusal by name rather than a silent success.
-ADM_USERS="$ADMPATH_DIR/users"
-printf '%s\n' 'dan admin ssh-ed25519 AAAAC3fixture dan@laptop' > "$ADM_USERS"
-admstub "$ADMPATH_DIR/no-visudo" useradd usermod groupadd
-check "preflight: users apply refuses a sudo-needing role when visudo is unreachable" 1 "visudo" \
-  adm_with "$ADMPATH_DIR/no-visudo" "$ROOT/commands/users-apply.sh" --file "$ADM_USERS" --yes
-# …and the refusal must land BEFORE the groups are converged, or the machine is
-# already half-changed when the operator reads it.
-check "preflight: …before any group is created" 1 "" \
-  adm_saw "$ADMPATH_DIR/no-visudo" 'rig-admin' \
-  "$ROOT/commands/users-apply.sh" --file "$ADM_USERS" --yes
-# A users file needing no sudo must NOT be refused for a missing visudo: the
-# guard has to be as narrow as the need, or it refuses healthy boxes.
-printf '%s\n' 'maria ops ssh-ed25519 AAAAC3fixture maria@mac' > "$ADMPATH_DIR/users-nosudo"
-check "preflight: …but a file with no sudo-backed role is not refused for visudo" 1 "" \
-  adm_saw "$ADMPATH_DIR/no-visudo" 'visudo' \
-  "$ROOT/commands/users-apply.sh" --file "$ADMPATH_DIR/users-nosudo" --yes
-
-# The fourth call site (#139 review): bootstrap-tenant adds the tenant user to
-# the docker group AFTER installing docker and node, so an unguarded PATH fails
-# it mid-convergence on a machine it has already changed.
-# staging-box because it is the one tenant role defined in rig's own tree: the
-# others resolve through the template registry, and a preflight test must not
-# depend on the network to reach the guard it is testing.
-admstub "$ADMPATH_DIR/no-any"
-check "preflight: bootstrap-tenant refuses a sbin-less PATH before it converges" 1 "usermod" \
-  adm_with "$ADMPATH_DIR/no-any" "$ROOT/commands/bootstrap-tenant.sh" staging-box
 rm -rf "$ADMPATH_DIR"
 
 # --- rig forgejo-runner (#109) ----------------------------------------------
@@ -3464,22 +3389,12 @@ check "forgejo-runner: --version refuses a path, not a release number" 2 "releas
   "$FR" --instance https://f.example.com --version ../../etc/passwd
 check "forgejo-runner: --version refuses a non-numeric pin" 2 "release number like" \
   "$FR" --instance https://f.example.com --version latest
-# Reaching a gate AFTER --version parsing is the proof a good pin got THROUGH
-# validation. Which gate depends on the uid: non-root hits "must run as root";
-# act/Forgejo jobs run as uid 0 (no `runner` account — #144), so they sail past
-# the root check and hit the unattended-token refuse instead. Both prove the
-# same thing. GitHub-hosted ubuntu-latest is non-root and takes the first arm.
-if [ "$(id -u)" -ne 0 ]; then
-  check "forgejo-runner: a plain release number passes validation" 1 "must run as root" \
-    "$FR" --instance https://f.example.com --version 12.13.2
-  check "forgejo-runner: a leading v is stripped before that check" 1 "must run as root" \
-    "$FR" --instance https://f.example.com --version v12.13.2
-else
-  check "forgejo-runner: a plain release number passes validation" 1 "FORGEJO_RUNNER_TOKEN is unset" \
-    env -u FORGEJO_RUNNER_TOKEN "$FR" --instance https://f.example.com --version 12.13.2
-  check "forgejo-runner: a leading v is stripped before that check" 1 "FORGEJO_RUNNER_TOKEN is unset" \
-    env -u FORGEJO_RUNNER_TOKEN "$FR" --instance https://f.example.com --version v12.13.2
-fi
+# Reaching the root check is the proof a good pin got THROUGH validation: this
+# runs as a normal user in CI, so "must run as root" is the next gate down.
+check "forgejo-runner: a plain release number passes validation" 1 "must run as root" \
+  "$FR" --instance https://f.example.com --version 12.13.2
+check "forgejo-runner: a leading v is stripped before that check" 1 "must run as root" \
+  "$FR" --instance https://f.example.com --version v12.13.2
 # A schemeless host and a repo URL are the two ways an operator mis-states the
 # instance, and only one of them would fail loudly on its own — a repo URL
 # registers somewhere subtly wrong instead. Both refuse by name.
@@ -3829,44 +3744,6 @@ check "forgejo-runner: an explicit --labels on a rerun warns it was not applied"
   grep -o -- "--labels was not applied" "$FR"
 check "forgejo-runner: that warning is gated on --labels being EXPLICIT" 0 "LABELS_EXPLICIT" \
   grep -o "LABELS_EXPLICIT" "$FR"
-# #144 option B: plain converge warns only for known *retired* defaults — not
-# for every RECORDED != current default (that would noise custom --labels
-# forever, including drill's Leg 3). Drive the recogniser against fixtures
-# (test/drill.sh extraction pattern) so a dead matcher cannot greppen green.
-check "forgejo-runner: plain converge warns on a known retired default label set" 0 "registered with an older rig default label set" \
-  grep -o "registered with an older rig default label set" "$FR"
-check "forgejo-runner: that warn says re-register only if you want the new label" 0 "re-register only if you want the new label" \
-  grep -o "re-register only if you want the new label" "$FR"
-PRE_144_LABELS='ubuntu-latest:docker://ghcr.io/catthehacker/ubuntu:act-22.04,docker:docker://node:22-bookworm'
-CURRENT_LABELS="$(sed -n "s/^DEFAULT_LABELS='\\(.*\\)'$/\\1/p" "$FR")"
-RETIRED_FNS="$(mktemp)"
-awk '/^labels_are_a_retired_default\(\) \{/,/^\}/' "$FR" > "$RETIRED_FNS"
-check "extraction guards the awk: labels_are_a_retired_default() landed" 0 "labels_are_a_retired_default() {" \
-  grep -F 'labels_are_a_retired_default() {' "$RETIRED_FNS"
-# shellcheck source=/dev/null
-. "$RETIRED_FNS"
-check "retired-default: the pre-#144 default is recognised" 0 "" \
-  labels_are_a_retired_default "$PRE_144_LABELS"
-check "retired-default: the CURRENT default is not drift" 1 "" \
-  labels_are_a_retired_default "$CURRENT_LABELS"
-check "retired-default: an operator's own --labels map is never drift" 1 "" \
-  labels_are_a_retired_default 'drill:docker://node:22-bookworm'
-check "retired-default: a near-miss of a past default is not a match" 1 "" \
-  labels_are_a_retired_default "${PRE_144_LABELS} "
-rm -f "$RETIRED_FNS"
-# Default map: slim ubuntu-latest (act), opt-in full, docker — pin the three
-# so a silent drop of the full rider or a flip back to full-as-default fails.
-check "forgejo-runner: DEFAULT_LABELS maps ubuntu-latest to act-22.04 (slim)" 0 "ubuntu-latest:docker://ghcr.io/catthehacker/ubuntu:act-22.04" \
-  grep -o "ubuntu-latest:docker://ghcr.io/catthehacker/ubuntu:act-22.04" "$FR"
-check "forgejo-runner: DEFAULT_LABELS offers ubuntu-latest-full as opt-in" 0 "ubuntu-latest-full:docker://ghcr.io/catthehacker/ubuntu:full-22.04" \
-  grep -o "ubuntu-latest-full:docker://ghcr.io/catthehacker/ubuntu:full-22.04" "$FR"
-check "forgejo-runner: DEFAULT_LABELS comment records the slim/full size measurement" 0 "54.5 GB" \
-  grep -o "54.5 GB" "$FR"
-# ci.yml must install shellcheck when the image lacks it (#144 option B).
-check "ci.yml: shellcheck step installs the tool when missing" 0 "command -v shellcheck" \
-  grep -o "command -v shellcheck" "$ROOT/.github/workflows/ci.yml"
-check "ci.yml: shellcheck install uses sudo (GitHub path; no-op on act as root)" 0 "sudo apt-get install -y shellcheck" \
-  grep -o "sudo apt-get install -y shellcheck" "$ROOT/.github/workflows/ci.yml"
 # The GitHub sibling is the precedent this restores — pin that it still scopes
 # its own write, so the two cannot drift apart again.
 gh_labels_write_is_scoped() {