diff --git a/.github/workflows/refs-guard.yml b/.github/workflows/refs-guard.yml
new file mode 100644
index 0000000..ef4964e
--- /dev/null
+++ b/.github/workflows/refs-guard.yml
@@ -0,0 +1,18 @@
+name: Refs guard
+
+on:
+  # Body edits are load-bearing: #200 gained its accidental closing keyword
+  # after the PR opened, with no new commit to wake ordinary CI (#218).
+  pull_request:
+    types: [opened, edited, reopened, synchronize]
+
+permissions:
+  contents: read
+  pull-requests: read
+
+jobs:
+  refs-not-closing:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: ./actions/refs-not-closing
diff --git a/actions/refs-not-closing/action.yml b/actions/refs-not-closing/action.yml
new file mode 100644
index 0000000..22c1f3f
--- /dev/null
+++ b/actions/refs-not-closing/action.yml
@@ -0,0 +1,58 @@
+name: Refs not closing
+description: >-
+  Refuse a pull request whose `Refs #N` promise contradicts GitHub's
+  closing-issue graph (#218). GitHub recognizes closing keywords anywhere
+  in a PR body, including ordinary prose and code spans; the action reads
+  the graph once and lets a pure script decide whether any Refs target is
+  already scheduled to close.
+runs:
+  using: composite
+  steps:
+    - name: refs targets are not closing
+      shell: bash
+      env:
+        GH_TOKEN: ${{ github.token }}
+        PR_NUMBER: ${{ github.event.pull_request.number }}
+      run: |
+        set -euo pipefail
+
+        owner="${GITHUB_REPOSITORY%%/*}"
+        name="${GITHUB_REPOSITORY#*/}"
+        [ -n "$PR_NUMBER" ] || {
+          echo "refs-not-closing: pull request number is unavailable" >&2
+          exit 1
+        }
+
+        facts="$(gh api graphql \
+          -f query='query($owner: String!, $name: String!, $number: Int!) {
+            repository(owner: $owner, name: $name) {
+              pullRequest(number: $number) {
+                body
+                closingIssuesReferences(first: 100) {
+                  nodes { number }
+                  pageInfo { hasNextPage }
+                }
+              }
+            }
+          }' \
+          -F owner="$owner" -F name="$name" -F number="$PR_NUMBER")"
+
+        body_file="$(mktemp)"
+        closing_file="$(mktemp)"
+        trap 'rm -f "$body_file" "$closing_file"' EXIT
+        jq -er '
+          .data.repository.pullRequest
+          | if . == null then error("pull request was not returned") else .body // "" end
+        ' <<<"$facts" >"$body_file"
+        jq -er '
+          .data.repository.pullRequest.closingIssuesReferences
+          | if .pageInfo.hasNextPage then
+              error("more than 100 closing issue references; refusing a partial verdict")
+            else
+              .nodes[].number
+            end
+        ' <<<"$facts" >"$closing_file"
+
+        mapfile -t closing_issues <"$closing_file"
+        bash "$GITHUB_ACTION_PATH/refs-not-closing.sh" \
+          "$body_file" "${closing_issues[@]}"
diff --git a/actions/refs-not-closing/refs-not-closing.sh b/actions/refs-not-closing/refs-not-closing.sh
new file mode 100755
index 0000000..946a6c8
--- /dev/null
+++ b/actions/refs-not-closing/refs-not-closing.sh
@@ -0,0 +1,116 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# refs-not-closing.sh <body-file> [<closing-issue-number> ...] — compare the
+# issues a PR promises merely to reference with GitHub's closing-issue graph
+# (#218). The graph is authoritative because it includes both closing
+# keywords and sidebar links. The body still matters: only an issue named by
+# `Ref #N` or `Refs #N` is protected, so an ordinary `Closes #N` PR remains
+# untouched.
+#
+# This decision stays network-free so test/refs-not-closing.test.sh can drive
+# the incident matrix offline. The composite action gathers both facts in one
+# GraphQL read and passes them here. A failed or partial read never reaches
+# this script: action.yml refuses it before asking for a verdict.
+
+body_file="${1:-}"
+shift || true
+
+[ -n "$body_file" ] && [ -f "$body_file" ] || {
+  echo "refs-not-closing: body file is missing or unreadable: ${body_file:-<none>}" >&2
+  exit 1
+}
+
+declare -A closing=()
+for issue in "$@"; do
+  case "$issue" in
+    ''|*[!0-9]*)
+      echo "refs-not-closing: invalid closing issue number: '$issue'" >&2
+      exit 1
+      ;;
+  esac
+  closing["$issue"]=1
+done
+
+mapfile -t refs_targets < <(
+  awk '
+    {
+      rest = tolower($0)
+      while (match(rest, /(^|[^[:alnum:]_])refs?[[:space:]]+#[0-9]+/)) {
+        token = substr(rest, RSTART, RLENGTH)
+        sub(/^.*#/, "", token)
+        print token + 0
+        rest = substr(rest, RSTART + RLENGTH)
+      }
+    }
+  ' "$body_file" | sort -nu
+)
+
+intersections=()
+for issue in "${refs_targets[@]}"; do
+  if [ -n "${closing[$issue]:-}" ]; then
+    intersections+=("$issue")
+  fi
+done
+
+if [ "${#intersections[@]}" -eq 0 ]; then
+  echo "refs-not-closing: no Refs target appears in GitHub's closing-issue graph"
+  exit 0
+fi
+
+sentence_for_issue() {
+  local issue="$1" mode="$2"
+  awk -v issue="$issue" -v mode="$mode" '
+    {
+      text = text separator $0
+      separator = "\n"
+    }
+    END {
+      count = split(text, sentence, /[.!?][[:space:]]+|\n+/)
+      if (mode == "closing") {
+        needle = "(^|[^[:alnum:]_])(close|closes|closed|fix|fixes|fixed|resolve|resolves|resolved)[[:space:]]+#[[:space:]]*" issue "([^0-9]|$)"
+      } else {
+        needle = "(^|[^[:alnum:]_])refs?[[:space:]]+#[[:space:]]*" issue "([^0-9]|$)"
+      }
+      for (i = 1; i <= count; i++) {
+        lower = tolower(sentence[i])
+        if (match(lower, needle)) {
+          matched = substr(sentence[i], RSTART, RLENGTH)
+          sub(/^[^[:alnum:]_]*/, "", matched)
+          sub(/[^0-9]*$/, "", matched)
+          gsub(/^[[:space:]]+|[[:space:]]+$/, "", sentence[i])
+          printf "%s\t%s\n", matched, sentence[i]
+          exit
+        }
+      }
+    }
+  ' "$body_file"
+}
+
+{
+  printf 'refs-not-closing: Refs target(s) also scheduled to close:'
+  printf ' #%s' "${intersections[@]}"
+  printf '\n'
+
+  for issue in "${intersections[@]}"; do
+    detail="$(sentence_for_issue "$issue" closing)"
+    if [ -z "$detail" ]; then
+      detail="$(sentence_for_issue "$issue" refs)"
+      printf "  #%s: GitHub reports a closing reference; no adjacent closing keyword was found, so inspect the Development sidebar link.\n" "$issue"
+    fi
+    if [ -n "$detail" ]; then
+      matched="${detail%%$'\t'*}"
+      sentence="${detail#*$'\t'}"
+      printf '    matched: %s\n' "$matched"
+      printf '    sentence: %s\n' "$sentence"
+    fi
+  done
+
+  cat <<'EOF'
+  A `Refs #N` PR must not close N. Remove the sidebar closing link or rewrite
+  an adjacent closing-keyword sentence so the number comes first (`#N is
+  closed by hand`) or the number is omitted (`triage closes the issue by
+  hand`). Backticks do not protect a closing keyword from GitHub's parser.
+EOF
+} >&2
+exit 1
diff --git a/test/refs-not-closing.test.sh b/test/refs-not-closing.test.sh
new file mode 100755
index 0000000..71696d7
--- /dev/null
+++ b/test/refs-not-closing.test.sh
@@ -0,0 +1,94 @@
+#!/usr/bin/env bash
+# Contract tests for actions/refs-not-closing (issue #218). Bodies and
+# closing-reference sets are fixtures: no network and no pull request are
+# involved. set -u, not -e: failures are behavior for the harness to inspect.
+set -u
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+# shellcheck source=test/harness.sh
+. "$ROOT/test/harness.sh"
+
+SCRIPT="$ROOT/actions/refs-not-closing/refs-not-closing.sh"
+ACTION="$ROOT/actions/refs-not-closing/action.yml"
+WORKFLOW="$ROOT/.github/workflows/refs-guard.yml"
+
+TMP="$(mktemp -d)"
+trap 'rm -rf "$TMP"' EXIT
+
+body() {
+  local name="$1"
+  shift
+  printf '%s\n' "$@" >"$TMP/$name.md"
+}
+
+guard() {
+  local name="$1"
+  shift
+  bash "$SCRIPT" "$TMP/$name.md" "$@"
+}
+
+body ref-5 'Refs #5'
+check "Refs target with empty closing set passes" 0 "no Refs target" guard ref-5
+check "Refs target with itself closing fails" 1 "#5" guard ref-5 5
+check "Refs target with another issue closing passes" 0 "no Refs target" guard ref-5 9
+
+body ordinary 'Closes #5'
+check "ordinary Closes PR remains green" 0 "no Refs target" guard ordinary 5
+
+body mixed 'Refs #5' '' 'This PR legitimately Closes #9.'
+check "Refs #5 plus Closes #9 remains green" 0 "no Refs target" guard mixed 9
+
+body prose 'Refs #5' '' 'Triage closes #5 by hand after the live proof.'
+check "closing prose for a Refs target fails" 1 "closes #5" guard prose 5
+check "failure prints the surrounding sentence" 1 \
+  "sentence: Triage closes #5 by hand after the live proof" guard prose 5
+check "failure offers number-first rewrite" 1 "#N is" guard prose 5
+check "failure offers number-free rewrite" 1 "closes the issue" guard prose 5
+
+body code-span 'Refs #5' '' 'The body must not contain `Closes #5` anywhere.'
+check "backticked closing keyword still fails" 1 "Closes #5" guard code-span 5
+check "backtick failure explains that code spans do not protect" 1 \
+  "Backticks do not protect" guard code-span 5
+
+body adjacency 'Refs #5' '' 'Triage closes #9 and #5 after the proof.'
+check "non-adjacent #5 does not join closing set #9" 0 "no Refs target" \
+  guard adjacency 9
+
+body empty ''
+check "empty body remains green" 0 "no Refs target" guard empty 5
+
+body incidents-211 'Refs #209' 'Triage closes #209 by hand.'
+check "#211 incident replays red" 1 "#209" guard incidents-211 209
+body incidents-214 'Refs #212' 'Triage closes #212 and #209 on that evidence.'
+check "#214 incident replays red" 1 "#212" guard incidents-214 212
+body incidents-200 'Refs #199' 'A later edit added `Closes #199`.'
+check "#200 incident replays red" 1 "#199" guard incidents-200 199
+
+for number in 207 191 190 176 165 164; do
+  body "incident-$number" "Refs #$number"
+  check "#$number incident replays green" 0 "no Refs target" \
+    guard "incident-$number"
+done
+
+check "missing body is a loud failure" 1 "missing or unreadable" \
+  bash "$SCRIPT" "$TMP/missing.md"
+check "invalid closing set is a loud failure" 1 "invalid closing issue" \
+  guard ref-5 nope
+
+# The action owns the network boundary. These structural assertions keep a
+# future edit from suppressing a failed/partial GraphQL read or splitting the
+# one authoritative query into several drifting reads.
+check "action performs exactly one GraphQL read" 0 "1" \
+  bash -c 'test "$(grep -c "gh api graphql" "$1")" -eq 1; printf 1' _ "$ACTION"
+check "action refuses a partial closing-reference page" 0 "hasNextPage" \
+  grep -F "hasNextPage" "$ACTION"
+check "action does not suppress GraphQL failure" 1 "" \
+  grep -E 'gh api graphql.*(\|\| true|\| true)' "$ACTION"
+
+check "workflow wakes on body edits" 0 "types: [opened, edited, reopened, synchronize]" \
+  grep -F "types: [opened, edited, reopened, synchronize]" "$WORKFLOW"
+check "workflow is pull_request-only" 1 "" grep -E '^  (push|pull_request_target|workflow_dispatch):' "$WORKFLOW"
+check "workflow grants read-only pull request access" 0 "pull-requests: read" \
+  grep -F "pull-requests: read" "$WORKFLOW"
+
+summary