fix(kbs): legacy subblock id migration + CI check (#3425)

* fix(kbs): legacy subblock id migration + CI check

* cleanup migration code

* address regex inaccuracy

.github/workflows/test-build.yml

@@ -90,6 +90,16 @@ jobs:
 
           echo "✅ All feature flags are properly configured"
 
+      - name: Check subblock ID stability
+        run: |
+          if [ "${{ github.event_name }}" = "pull_request" ]; then
+            BASE_REF="origin/${{ github.base_ref }}"
+            git fetch --depth=1 origin "${{ github.base_ref }}" 2>/dev/null || true
+          else
+            BASE_REF="HEAD~1"
+          fi
+          bun run apps/sim/scripts/check-subblock-id-stability.ts "$BASE_REF"
+
       - name: Lint code
         run: bun run lint:check