Add get-workflow-ref action

Resolves the ref a caller used to invoke a reusable workflow from this
repo by parsing the caller's workflow file. No API calls or extra
permissions needed — works with both public and private repos.

This is needed because reusable workflows cannot access their own
invocation ref via the github context (github.workflow_ref and
github.workflow_sha both point to the caller's repo).

Co-Authored-By: roachdev-claude <roachdev-claude-bot@cockroachlabs.com>

Author: fantapop

get-workflow-ref/action.yml

@@ -0,0 +1,65 @@
+name: Get Workflow Ref
+description: >
+  Resolve the ref that a caller used to invoke a reusable workflow from this
+  repo. Parses the caller's workflow file — no API calls or extra permissions
+  needed.
+
+inputs:
+  workflow_name:
+    description: >
+      Substring to match in the caller's uses line (e.g.
+      "cockroachdb/actions/.github/workflows/github-issue-autosolve.yml").
+    required: true
+
+outputs:
+  ref:
+    description: The ref (tag, branch, or SHA) from the caller's uses line.
+    value: ${{ steps.resolve.outputs.ref }}
+
+runs:
+  using: "composite"
+  steps:
+    - name: Checkout caller workflows
+      uses: actions/checkout@v5
+      with:
+        sparse-checkout: .github/workflows
+        persist-credentials: false
+
+    - name: Resolve ref from caller workflow
+      id: resolve
+      shell: bash
+      run: |
+        workflow_ref="${WORKFLOW_REF}"
+        workflow_path="${workflow_ref#"${REPO}/"}"
+        workflow_path="${workflow_path%"@${REF}"}"
+
+        if [ ! -f "$workflow_path" ]; then
+          echo "::error::Could not find caller workflow at: $workflow_path"
+          exit 1
+        fi
+
+        match="$(grep "$WORKFLOW_NAME" "$workflow_path" | head -1)"
+        if [ -z "$match" ]; then
+          echo "::error::Could not find '$WORKFLOW_NAME' in $workflow_path"
+          exit 1
+        fi
+
+        # Handle local reference (./): use the caller's own ref.
+        if [[ "$match" == *"./.github/workflows"* ]]; then
+          ref="${REF}"
+        else
+          ref="$(echo "$match" | sed 's/.*@//' | awk '{print $1}')"
+        fi
+
+        if [ -z "$ref" ]; then
+          echo "::error::Could not parse ref from: $match"
+          exit 1
+        fi
+
+        echo "ref=$ref" >> "$GITHUB_OUTPUT"
+        echo "Resolved workflow ref: $ref"
+      env:
+        WORKFLOW_REF: ${{ github.workflow_ref }}
+        REPO: ${{ github.repository }}
+        REF: ${{ github.ref }}
+        WORKFLOW_NAME: ${{ inputs.workflow_name }}