diff --git a/action.yml b/action.yml
index c54de83..f80b342 100644
--- a/action.yml
+++ b/action.yml
@@ -104,7 +104,10 @@ runs:
         annotations_source="$json_file"
         rating_source="$json_file"
         if [ "${MESH_DIFF:-false}" = "true" ] && [ "${GITHUB_EVENT_NAME:-}" = "pull_request" ]; then
-          base_sha="$(jq -r '.pull_request.base.sha // empty' "$GITHUB_EVENT_PATH")"
+          # Read the PR base SHA from the event payload with Node (always
+          # present — this is a Node action) rather than jq, which is not
+          # guaranteed on self-hosted or minimal runners.
+          base_sha="$(node -e 'try{const fs=require("node:fs");const e=JSON.parse(fs.readFileSync(process.env.GITHUB_EVENT_PATH,"utf8"));process.stdout.write(e.pull_request?.base?.sha ?? "")}catch{process.stdout.write("")}')"
           if [ -n "$base_sha" ]; then
             git fetch --no-tags --depth=1 origin "$base_sha" 2>/dev/null || true
             base_dir="${RUNNER_TEMP:-.}/policymesh-base-worktree"
@@ -145,29 +148,37 @@ runs:
         # pull_request event. Uses an HTML marker to find-and-update the
         # existing comment in place rather than spam a new one per push.
         if [ -n "${MESH_GITHUB_TOKEN:-}" ] && [ "${GITHUB_EVENT_NAME:-}" = "pull_request" ]; then
-          pr_number="$(jq -r '.pull_request.number // empty' "$GITHUB_EVENT_PATH")"
-          if [ -n "$pr_number" ]; then
-            marker='<!-- policymesh:pr-summary -->'
-            comment_file="${RUNNER_TEMP:-.}/policymesh-comment.md"
-            {
-              printf '%s\n\n' "$marker"
-              cat "$report_file"
-            } > "$comment_file"
-
-            existing="$(GH_TOKEN="$MESH_GITHUB_TOKEN" gh api \
-              "repos/${GITHUB_REPOSITORY}/issues/${pr_number}/comments" \
-              --paginate \
-              --jq ".[] | select(.body != null and (.body | contains(\"$marker\"))) | .id" \
-              | head -n 1)"
-
-            if [ -n "$existing" ]; then
-              GH_TOKEN="$MESH_GITHUB_TOKEN" gh api -X PATCH \
-                "repos/${GITHUB_REPOSITORY}/issues/comments/${existing}" \
-                -F body=@"$comment_file" > /dev/null
-            else
-              GH_TOKEN="$MESH_GITHUB_TOKEN" gh api -X POST \
+          if ! command -v gh >/dev/null 2>&1; then
+            # gh is preinstalled on GitHub-hosted runners but may be absent
+            # on self-hosted or minimal images. Degrade gracefully rather
+            # than failing the step — the Markdown report is already in the
+            # step summary.
+            echo "::notice::PolicyMesh: sticky PR comment skipped because the GitHub CLI (gh) is not available on this runner. The Markdown report is still in the step summary."
+          else
+            pr_number="$(node -e 'try{const fs=require("node:fs");const e=JSON.parse(fs.readFileSync(process.env.GITHUB_EVENT_PATH,"utf8"));process.stdout.write(String(e.pull_request?.number ?? ""))}catch{process.stdout.write("")}')"
+            if [ -n "$pr_number" ]; then
+              marker='<!-- policymesh:pr-summary -->'
+              comment_file="${RUNNER_TEMP:-.}/policymesh-comment.md"
+              {
+                printf '%s\n\n' "$marker"
+                cat "$report_file"
+              } > "$comment_file"
+
+              existing="$(GH_TOKEN="$MESH_GITHUB_TOKEN" gh api \
                 "repos/${GITHUB_REPOSITORY}/issues/${pr_number}/comments" \
-                -F body=@"$comment_file" > /dev/null
+                --paginate \
+                --jq ".[] | select(.body != null and (.body | contains(\"$marker\"))) | .id" \
+                | head -n 1)"
+
+              if [ -n "$existing" ]; then
+                GH_TOKEN="$MESH_GITHUB_TOKEN" gh api -X PATCH \
+                  "repos/${GITHUB_REPOSITORY}/issues/comments/${existing}" \
+                  -F body=@"$comment_file" > /dev/null
+              else
+                GH_TOKEN="$MESH_GITHUB_TOKEN" gh api -X POST \
+                  "repos/${GITHUB_REPOSITORY}/issues/${pr_number}/comments" \
+                  -F body=@"$comment_file" > /dev/null
+              fi
             fi
           fi
         fi
diff --git a/package-lock.json b/package-lock.json
index 963bbc4..5e16887 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -17,6 +17,9 @@
       "devDependencies": {
         "@types/node": "^24.0.0",
         "typescript": "^5.9.3"
+      },
+      "engines": {
+        "node": ">=20"
       }
     },
     "node_modules/@types/node": {
diff --git a/package.json b/package.json
index 514f4d2..11b82c6 100644
--- a/package.json
+++ b/package.json
@@ -38,5 +38,8 @@
     "@types/node": "^24.0.0",
     "typescript": "^5.9.3"
   },
+  "engines": {
+    "node": ">=20"
+  },
   "license": "MIT"
 }
diff --git a/test/workflow.test.mjs b/test/workflow.test.mjs
index aee1f66..b48e6ef 100644
--- a/test/workflow.test.mjs
+++ b/test/workflow.test.mjs
@@ -153,6 +153,28 @@ test('published Action runs the bundled CLI without installing or rebuilding its
   assert.ok(trackedDistFiles.includes('dist/audit.js'));
 });
 
+test('action.yml reads the PR event with Node and guards the GitHub CLI', async () => {
+  const action = await readFile(join(packageRoot, 'action.yml'), 'utf8');
+
+  // No dependency on the standalone jq binary for parsing the event payload
+  // — minimal / self-hosted runners may not have it.
+  assert.doesNotMatch(action, /jq -r '\.pull_request/);
+  // PR base SHA + number are read with Node straight from the event JSON.
+  assert.match(action, /process\.env\.GITHUB_EVENT_PATH/);
+  assert.match(action, /pull_request\?\.base\?\.sha/);
+  // gh is guarded so a runner without it degrades to a notice, not a failure.
+  assert.match(action, /command -v gh/);
+});
+
+test('package.json and lockfile declare a supported Node engine', async () => {
+  const packageJson = JSON.parse(await readFile(join(packageRoot, 'package.json'), 'utf8'));
+  const packageLock = JSON.parse(await readFile(join(packageRoot, 'package-lock.json'), 'utf8'));
+
+  assert.deepEqual(packageJson.engines, { node: '>=20' });
+  // Keep the lockfile's root entry in sync so `npm ci` does not warn on drift.
+  assert.deepEqual(packageLock.packages[''].engines, { node: '>=20' });
+});
+
 test('CI workflow builds and tests PolicyMesh', async () => {
   const workflow = await readFile(join(packageRoot, '.github', 'workflows', 'ci.yml'), 'utf8');