diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 37a6882..c17c424 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -31,6 +31,10 @@ jobs:
         # The pin rules (issue #9; #1 D3): a stale CEREMONY_SELF_REF fails
         # CI here, not a consumer's release.
         run: bash .github/scripts/self-ref-check.sh
+      - name: Documentation availability markers
+        # Five stale markers survived the tags that shipped their machinery
+        # (#221); #238 makes the release candidate reject that drift.
+        run: bash .github/scripts/marker-check.sh
       - name: Tests
         env:
           # The npm-backed version_write case may skip locally when npm is
diff --git a/changelog.d/238.md b/changelog.d/238.md
new file mode 100644
index 0000000..6805c0b
--- /dev/null
+++ b/changelog.d/238.md
@@ -0,0 +1,4 @@
+### Added
+
+- Guard documentation availability markers against missing issue citations
+  and release candidates that already ship the cited work (#238).
diff --git a/test/marker-check.test.sh b/test/marker-check.test.sh
new file mode 100644
index 0000000..7017e84
--- /dev/null
+++ b/test/marker-check.test.sh
@@ -0,0 +1,94 @@
+#!/usr/bin/env bash
+# Contract tests for .github/scripts/marker-check.sh (issue #238). The guard
+# is driven against tracked fixture trees; set -u, not -e, because 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"
+
+CHECK="$ROOT/.github/scripts/marker-check.sh"
+TMP="$(mktemp -d)"
+trap 'rm -rf "$TMP"' EXIT
+
+fixture() {
+  local name="$1" version="$2"
+  mkdir -p "$TMP/$name/docs" "$TMP/$name/changelog.d"
+  git -C "$TMP/$name" init -q
+  printf '%s\n' "$version" >"$TMP/$name/VERSION"
+  printf '# Changelog\n\n## 0.5.0 — 2026-08-03\n\n- Shipped (#221).\n' \
+    >"$TMP/$name/CHANGELOG.md"
+}
+
+run_check() {
+  git -C "$TMP/$1" add .
+  bash "$CHECK" "$TMP/$1"
+}
+
+fixture wrapped 0.6.0-dev
+cat >"$TMP/wrapped/docs/CONSUMERS.md" <<'EOF'
+The new guard remains **unreleased**
+(#238) until the next tag.
+EOF
+check "a wrapped local citation is accepted" 0 "agree with the tree" \
+  run_check wrapped
+
+fixture uncited 0.6.0-dev
+printf 'The new guard remains **unreleased** for now.\n' \
+  >"$TMP/uncited/docs/CONSUMERS.md"
+check "an uncited marker fails on a dev tree with file and line" 1 \
+  "docs/CONSUMERS.md:1" run_check uncited
+
+fixture shipped 0.6.0
+printf 'The new guard remains **unreleased** (#224).\n' \
+  >"$TMP/shipped/docs/CONSUMERS.md"
+cat >"$TMP/shipped/CHANGELOG.md" <<'EOF'
+# Changelog
+
+## 0.6.0 — 2026-08-03
+
+- The guard shipped (#224).
+
+## 0.5.0 — 2026-08-02
+
+- Older work (#999).
+EOF
+check "a release rejects a marker cited by its top section" 1 \
+  "docs/CONSUMERS.md:1: **unreleased** (#224)" run_check shipped
+
+fixture not-shipped 0.6.0
+printf 'Future work remains **unreleased** (#999).\n' \
+  >"$TMP/not-shipped/docs/CONSUMERS.md"
+cp "$TMP/shipped/CHANGELOG.md" "$TMP/not-shipped/CHANGELOG.md"
+check "a release keeps a marker absent from its top section" 0 \
+  "agree with the tree" run_check not-shipped
+
+fixture dev-shipped 0.6.0-dev
+printf 'Future work remains **unreleased** (#224).\n' \
+  >"$TMP/dev-shipped/docs/CONSUMERS.md"
+cp "$TMP/shipped/CHANGELOG.md" "$TMP/dev-shipped/CHANGELOG.md"
+check "a dev tree does not compare markers with shipped sections" 0 \
+  "agree with the tree" run_check dev-shipped
+
+fixture cross-repo 0.6.0
+printf 'Crew work remains **unreleased** (crew#293).\n' \
+  >"$TMP/cross-repo/docs/CONSUMERS.md"
+cat >"$TMP/cross-repo/CHANGELOG.md" <<'EOF'
+# Changelog
+
+## 0.6.0 — 2026-08-03
+
+- Local work shipped (#293).
+EOF
+check "a cross-repo citation is valid and ignored by release comparison" 0 \
+  "agree with the tree" run_check cross-repo
+
+fixture exclusions 0.6.0-dev
+printf '# Notes\n\n## Unreleased\n' >"$TMP/exclusions/NOTES.md"
+printf -- '- A fragment may say **unreleased** without being documentation.\n' \
+  >"$TMP/exclusions/changelog.d/999.md"
+check "headings and changelog fragments do not trip the guard" 0 \
+  "agree with the tree" run_check exclusions
+
+summary