fix(ci): wait for mysql to accept queries before db migration (#35631)

.github/workflows/db-migration-test.yml

@@ -110,6 +110,28 @@ jobs:
           sed -i 's/DB_PORT=5432/DB_PORT=3306/' .env
           sed -i 's/DB_USERNAME=postgres/DB_USERNAME=root/' .env
 
+      # hoverkraft-tech/compose-action@v2.6.0 only waits for `docker compose up -d`
+      # to return (container processes started); it does not wait on healthcheck
+      # status. mysql:8.0's first-time init takes 15-30s, so without an explicit
+      # wait the migration runs while InnoDB is still initialising and gets
+      # killed with "Lost connection during query". Poll a real SELECT until it
+      # succeeds.
+      - name: Wait for MySQL to accept queries
+        run: |
+          set +e
+          for i in $(seq 1 60); do
+            if docker run --rm --network host mysql:8.0 \
+                mysql -h 127.0.0.1 -P 3306 -uroot -pdifyai123456 \
+                -e 'SELECT 1' >/dev/null 2>&1; then
+              echo "MySQL ready after ${i}s"
+              exit 0
+            fi
+            sleep 1
+          done
+          echo "MySQL not ready after 60s; dumping container logs:"
+          docker compose -f docker/docker-compose.middleware.yaml --profile mysql logs --tail=200 db_mysql
+          exit 1
+
       - name: Run DB Migration
         env:
           DEBUG: true