fix(workflows): harden pr-labels-ci.yml against fork-PR shell injection (#332)

.github/workflows/pr-labels-ci.yml

@@ -49,20 +49,22 @@ jobs:
       - name: Promote to Ready for QA
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          REPO: ${{ github.repository }}
+          RUN_ID: ${{ github.event.workflow_run.id }}
+          HEAD_BRANCH: ${{ github.event.workflow_run.head_branch }}
         run: |
-          REPO=${{ github.repository }}
-
           # Look up the associated PR.
           # The API can 404 after a force-push (orphaned run).
           # Capture output only on success so 404 body doesn't leak into $PR.
           PR=""
-          API_OUT=$(gh api "repos/$REPO/actions/runs/${{ github.event.workflow_run.id }}/pull_requests" \
+          API_OUT=$(gh api "repos/$REPO/actions/runs/$RUN_ID/pull_requests" \
             --jq '.[0].number // empty' 2>&1) && PR="$API_OUT" || true
 
           # Fallback: pull_requests array is empty for dependabot PRs.
-          # Search by head branch instead.
+          # Search by head branch instead. HEAD_BRANCH comes via env
+          # (not a direct GHA expression) because fork PR branch names
+          # are contributor-controlled and allow shell metacharacters.
           if [ -z "$PR" ]; then
-            HEAD_BRANCH=${{ github.event.workflow_run.head_branch }}
             PR=$(gh pr list --repo "$REPO" --head "$HEAD_BRANCH" --state open \
               --json number --jq '.[0].number // empty' 2>/dev/null) || true
           fi
@@ -103,15 +105,17 @@ jobs:
       - name: Set CI Failed
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          REPO: ${{ github.repository }}
+          RUN_ID: ${{ github.event.workflow_run.id }}
+          HEAD_BRANCH: ${{ github.event.workflow_run.head_branch }}
         run: |
-          REPO=${{ github.repository }}
-
           PR=""
-          API_OUT=$(gh api "repos/$REPO/actions/runs/${{ github.event.workflow_run.id }}/pull_requests" \
+          API_OUT=$(gh api "repos/$REPO/actions/runs/$RUN_ID/pull_requests" \
             --jq '.[0].number // empty' 2>&1) && PR="$API_OUT" || true
 
+          # HEAD_BRANCH comes via env (not a direct GHA expression)
+          # because fork PR branch names are contributor-controlled.
           if [ -z "$PR" ]; then
-            HEAD_BRANCH=${{ github.event.workflow_run.head_branch }}
             PR=$(gh pr list --repo "$REPO" --head "$HEAD_BRANCH" --state open \
               --json number --jq '.[0].number // empty' 2>/dev/null) || true
           fi

CHANGELOG.md

@@ -8,6 +8,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Security
+- **Harden `pr-labels-ci.yml` against shell injection via fork-PR branch names.** Contributor-controlled values (`github.event.workflow_run.head_branch`, `.id`, `github.repository`) previously inlined directly into `run:` blocks as `${{ ... }}` expressions. Git refnames permit shell metacharacters (`$`, backtick, `;`, `&`, `|`), so a malicious fork branch name would render as executed shell after GHA's queue-time substitution. All such values now route through step-level `env:` and are referenced as shell variables (`"$HEAD_BRANCH"`, `"$REPO"`, `"$RUN_ID"`). Cascaded from [cmeans/mcp-clipboard#88](https://github.com/cmeans/mcp-clipboard/pull/88) hardening. Closes [#332](https://github.com/cmeans/mcp-awareness/issues/332).
+- **Pre-empt the "literal `${{ }}` in shell comments" parser trap** that would have surfaced the moment the hardening above landed with placeholder comments. GHA's queue-time parser substitutes `${{ ... }}` everywhere inside `run:` blocks — including inside shell `#` comments — and rejects empty expressions with `An expression was expected` on `workflow_dispatch` / fresh-repo registration. The hardening cascade uses comment wording that avoids literal `${{ }}` entirely. Root cause diagnosed in [cmeans/yt-dont-recommend#28](https://github.com/cmeans/yt-dont-recommend/issues/28); cascade source is [cmeans/mcp-clipboard#92](https://github.com/cmeans/mcp-clipboard/pull/92).
+
 ## [0.18.0] - 2026-04-16
 
 ### Added