fix(vllm): generate protobuf 6 compatible stubs (#10944)

Pin vLLM protogen to grpcio-tools 1.78.0 so its generated code remains importable by protobuf 6.33.x, and remove stale generated artifacts before regeneration.

Closes #10940

Assisted-by: Codex:gpt-5 [Codex]

Co-authored-by: localai-org-maint-bot <306269227+localai-org-maint-bot@users.noreply.github.com>

Author: localai-org-maint-bot

backend/python/common/libbackend.sh

@@ -407,12 +407,18 @@ function runProtogen() {
     # protobuf runtime lower (vLLM pins it to 6.33.6), crashing the backend with
     # "grpc service not ready" before it ever loads a model. Pinning
     # grpcio-tools to the installed grpcio version keeps the gencode in step with
-    # the runtime. Falls back to unpinned when grpcio isn't installed yet.
+    # the runtime. Backends whose protobuf runtime trails grpcio can set
+    # GRPCIO_TOOLS_VERSION to the newest generator their runtime accepts. Falls
+    # back to unpinned when grpcio isn't installed yet.
     # See mudler/LocalAI#10718.
     local grpcio_tools_spec="grpcio-tools"
     local grpcio_version
-    grpcio_version="$(python -c 'import importlib.metadata as m; print(m.version("grpcio"))' 2>/dev/null || true)"
-    if [ -n "${grpcio_version}" ]; then
+    if [ -n "${GRPCIO_TOOLS_VERSION:-}" ]; then
+        grpcio_tools_spec="grpcio-tools==${GRPCIO_TOOLS_VERSION}"
+    else
+        grpcio_version="$(python -c 'import importlib.metadata as m; print(m.version("grpcio"))' 2>/dev/null || true)"
+    fi
+    if [ "${grpcio_tools_spec}" = "grpcio-tools" ] && [ -n "${grpcio_version}" ]; then
         grpcio_tools_spec="grpcio-tools==${grpcio_version}"
     fi
 
@@ -422,6 +428,7 @@ function runProtogen() {
         uv pip install "${grpcio_tools_spec}"
     fi
     pushd "${EDIR}" >/dev/null
+        rm -f backend_pb2.py backend_pb2.pyi backend_pb2_grpc.py
         # use the venv python (ensures correct interpreter & sys.path)
         python -m grpc_tools.protoc -I../../ -I./ --python_out=. --grpc_python_out=. backend.proto
     popd >/dev/null

backend/python/vllm/install.sh

@@ -3,6 +3,12 @@ set -e
 
 EXTRA_PIP_INSTALL_FLAGS="--no-build-isolation"
 
+# grpcio 1.82 bundles protoc 7.x, while vLLM's resolved protobuf runtime is
+# still 6.33.x. Generate the backend stubs with the newest grpcio-tools release
+# that emits protobuf 6.x gencode; the newer grpcio runtime can consume those
+# stubs, but protobuf 6.x cannot import 7.x gencode.
+export GRPCIO_TOOLS_VERSION="1.78.0"
+
 # Avoid to overcommit the CPU during build
 # https://github.com/vllm-project/vllm/issues/20079
 # https://docs.vllm.ai/en/v0.8.3/serving/env_vars.html