# OpenVINO NPU reranker service

Local-first cross-encoder reranker prototype for second-stage RAG ranking.

- Default bind: `127.0.0.1:18818`
- Default model: `cross-encoder/ms-marco-MiniLM-L6-v2`
- Default device: `NPU`
- Model cache: `/home/will/.cache/openvino-models/rerankers/ms-marco-MiniLM-L6-v2-int8-ov/`
- NPU proof: `/sys/class/accel/accel0/device/npu_busy_time_us` delta before/after inference

This service is intentionally not wired into live RAG by default.

## Files

- `SPEC.md` — endpoint/CLI contract, model/runtime recommendation, smoke/NPU proof plan, RAG integration plan, docs implications, and no-go criteria.
- `server.py` — stdlib HTTP OpenVINO Runtime service with fail-fast localhost listener conflict checks and request validation.
- `smoke.py` — non-private API/ranking/NPU busy-time smoke test.
- `tests/test_server_validation.py` — stdlib unit checks for request validation and listener conflict detection.
- `openvino-reranker.service` — optional user-systemd unit.

## One-time setup

Use a separate venv so the existing Whisper/embeddings NPU venv is not perturbed:

```bash
python -m venv /home/will/.venvs/openvino-reranker
source /home/will/.venvs/openvino-reranker/bin/activate
python -m pip install -U pip
python -m pip install "openvino>=2026.2" "optimum-intel[openvino]" transformers tokenizers nncf numpy
```

Export the model:

```bash
source /home/will/.venvs/openvino-reranker/bin/activate
optimum-cli export openvino \
  --model cross-encoder/ms-marco-MiniLM-L6-v2 \
  --task text-classification \
  --weight-format int8 \
  --trust-remote-code false \
  /home/will/.cache/openvino-models/rerankers/ms-marco-MiniLM-L6-v2-int8-ov
```

If INT8 export or NPU compile fails, export an FP16/FP32 IR to a separate directory and point `OPENVINO_RERANKER_MODEL_DIR` at it while debugging. Do not overwrite existing vector/RAG/Chroma collections.

## Run in foreground

Check the port and NPU counter first:

```bash
ss -ltnp | grep ':18818 ' || true
cat /sys/class/accel/accel0/device/npu_busy_time_us
```

Start locally:

```bash
source /home/will/.venvs/openvino-reranker/bin/activate
OPENVINO_RERANKER_HOST=127.0.0.1 \
OPENVINO_RERANKER_PORT=18818 \
OPENVINO_RERANKER_DEVICE=NPU \
OPENVINO_RERANKER_MODEL_DIR=/home/will/.cache/openvino-models/rerankers/ms-marco-MiniLM-L6-v2-int8-ov \
python /home/will/lab/swarm/openvino-reranker-npu/server.py
```

Startup performs a non-private smoke inference and fails closed when `OPENVINO_RERANKER_DEVICE=NPU` but `npu_busy_time_us` does not increase. It also checks whether the requested listener can bind before compiling the OpenVINO model, so obvious port conflicts fail fast; the real server bind still happens immediately after model load.

## API

Health:

```bash
curl -sS http://127.0.0.1:18818/healthz | jq
curl -sS http://127.0.0.1:18818/readyz | jq
```

Rerank:

```bash
curl -sS http://127.0.0.1:18818/rerank \
  -H 'Content-Type: application/json' \
  -d '{
    "query":"how do I verify OpenVINO NPU usage?",
    "documents":[
      {"id":"good","text":"Check /sys/class/accel/accel0/device/npu_busy_time_us before and after inference."},
      {"id":"bad","text":"This note is about making sourdough starter."}
    ],
    "top_k":2
  }' | jq
```

Compatibility alias:

```bash
curl -sS http://127.0.0.1:18818/v1/rerank \
  -H 'Content-Type: application/json' \
  -d '{"model":"local-reranker","query":"npu busy time","documents":["OpenVINO NPU busy time proves accelerator use."],"top_n":1}' | jq
```

## Smoke test

```bash
source /home/will/.venvs/openvino-reranker/bin/activate
python /home/will/lab/swarm/openvino-reranker-npu/smoke.py --url http://127.0.0.1:18818
```

Expected:

- `/readyz` is HTTP 200 and reports `device=NPU`.
- Each fixture returns `ok=true` and a sorted `results` list.
- The top result matches the non-private fixture expectation.
- Response and sysfs `npu_busy_delta_us` are positive.

## Validation checks

```bash
source /home/will/.venvs/openvino-reranker/bin/activate
PYTHONPATH=/home/will/lab/swarm/openvino-reranker-npu \
  python -m unittest discover -s /home/will/lab/swarm/openvino-reranker-npu/tests
```

These checks do not compile the OpenVINO model; they cover request validation and fail-fast listener conflict detection.

## Optional systemd user service

Install the unit only after the foreground command and smoke test pass:

```bash
cp /home/will/lab/swarm/openvino-reranker-npu/openvino-reranker.service /home/will/.config/systemd/user/openvino-reranker.service
systemctl --user daemon-reload
systemctl --user start openvino-reranker.service
systemctl --user status openvino-reranker.service --no-pager
journalctl --user -u openvino-reranker.service -n 100 --no-pager
```

Do not enable or integrate it into live RAG without explicit approval.

## Optional RAG integration plan (disabled by default)

RAG should keep vector search against `obsidian_bge_npu` unchanged, retrieve a larger candidate set, and call this service as a read-only request-time second stage. Suggested disabled-by-default knobs:

```text
RAG_RERANK_ENABLED=false
RAG_RERANK_URL=http://127.0.0.1:18818/rerank
RAG_RERANK_INITIAL_K=20
RAG_RERANK_TOP_K=5
RAG_RERANK_TIMEOUT_MS=3000
```

On reranker timeout/error, fall back to vector order and include metadata such as `rerank_error`; do not mutate or reindex Chroma collections.