fix(sglang): stop the elastic-EP scale-up worker crash-looping at startup

tests/fault_tolerance/deploy/templates/sglang/run_sglang_elastic_ep_scale_up_test.sh

@@ -167,6 +167,7 @@ launch_joiner() {
       --elastic-ep-backend mooncake --mooncake-ib-device $IB_DEVICE \
       --enable-eplb --ep-num-redundant-experts 24 \
       --elastic-ep-initial-size 4 --max-ep-size 8 \
+      --cuda-graph-backend-decode disabled --cuda-graph-backend-prefill disabled \
       --elastic-ep-join-mode scale --elastic-ep-join-rank-offset $rank_offset \
       --dist-init-addr $DIST_INIT_ADDR \
       --host 127.0.0.1 --port $((30000 + rank_offset)) \

tests/fault_tolerance/deploy/templates/sglang/sglang_elastic_ep.yaml

@@ -31,6 +31,8 @@
 #     --mooncake-ib-device to the node's IB device list before applying.
 #   * DYN_SYSTEM_ENABLED=true so the leader exposes the :9090 system server that
 #     serves /engine/control/*.
+#   * BOTH the decode and the prefill CUDA graph disabled, passed explicitly
+#     below: SGLang asserts this for elastic-EP scale-up and exits on startup.
 #
 # The joining group is NOT launched by the operator yet (that orchestration is
 # tracked separately). The accompanying run_sglang_elastic_ep_scale_up_test.sh
@@ -128,6 +130,10 @@ spec:
             - "4"
             - --max-ep-size
             - "8"
+            - --cuda-graph-backend-decode
+            - disabled
+            - --cuda-graph-backend-prefill
+            - disabled
             # Stable rendezvous address the joining group dials on scale-up.
             # Sourced from SGLANG_ELASTIC_SCALE_DIST_INIT (single source of truth).
             - --dist-init-addr