fix(backends): pin grpcio-tools to installed grpcio in runProtogen (protobuf gencode mismatch)

[localai-bot]

Problem

The vLLM backend (all accelerations) fails to start with:

google.protobuf.runtime_version.VersionError: Detected incompatible Protobuf
Gencode/Runtime versions when loading backend.proto: gencode 7.35.0 runtime 6.33.6.
Runtime version cannot be older than the linked gencode version.

The backend crashes on import backend_pb2 before it can serve, surfacing to the user as failed to load model with internal loader: grpc service not ready.

Reported as a ROCm / R9700 gfx1201 failure (#10718), but it is not GPU-specific — the process never reaches any GPU code. It affects every vLLM variant (and any Python backend that caps the protobuf runtime below the latest grpcio-tools gencode).

Root cause

runProtogen (backend/python/common/libbackend.sh) runs after the backend's requirements are installed, and installs grpcio-tools unpinned:

uv pip install grpcio-tools   # pulls the newest release

The protoc bundled in the newest grpcio-tools stamps backend_pb2.py with Protobuf gencode 7.35.0. vLLM's dependencies pin the protobuf runtime down to 6.33.6. Protobuf enforces runtime >= gencode at import, so the generated module refuses to load.

Fix

Pin grpcio-tools to the grpcio version the backend already installed — the two are released in lockstep, so the bundled protoc's gencode stays in step with the protobuf runtime. Falls back to unpinned when grpcio isn't present (behaviour unchanged for those backends).

grpcio_version="$(python -c 'import importlib.metadata as m; print(m.version("grpcio"))' 2>/dev/null || true)"
[ -n "$grpcio_version" ] && grpcio_tools_spec="grpcio-tools==${grpcio_version}"

Testing

• bash -n clean; shellcheck -S warning reports nothing new on the changed lines (pre-existing findings elsewhere untouched).
• Fallback path verified (grpcio absent → unpinned, as before).
• Full runtime validation requires a backend image build (ROCm/vLLM) — CI territory; cannot be reproduced locally.

Closes #10718

🤖 Generated with Claude Code