P2.2+P2.3: NATS offload node-worker + router offload integration

Node Worker (services/node-worker/):
- NATS subscriber for node.{NODE_ID}.llm.request / vision.request
- Canonical JobRequest/JobResponse envelope (Pydantic)
- Idempotency cache (TTL 10min) with inflight dedup
- Deadline enforcement (DEADLINE_EXCEEDED on expired jobs)
- Concurrency limiter (semaphore, returns busy)
- Ollama + Swapper vision providers

Router offload (services/router/offload_client.py):
- NATS req/reply with configurable retries
- Circuit breaker per node+type (3 fails/60s → open 120s)
- Concurrency semaphore for remote requests

Model selection (services/router/model_select.py):
- exclude_nodes parameter for circuit-broken nodes
- force_local flag for fallback re-selection
- Integrated circuit breaker state awareness

Router /infer pipeline:
- Remote offload path when NCS selects remote node
- Automatic fallback: exclude failed node → force_local re-select
- Deadline propagation from router to node-worker

Tests: 17 unit tests (idempotency, deadline, circuit breaker)
Docs: ops/offload_routing.md (subjects, envelope, verification)
Made-with: Cursor

services/node-worker/providers/swapper_vision.py

@@ -0,0 +1,42 @@
+"""Swapper vision provider for node-worker."""
+import logging
+from typing import Any, Dict, List, Optional
+
+import httpx
+
+from config import SWAPPER_URL, DEFAULT_VISION
+
+logger = logging.getLogger("provider.swapper_vision")
+
+
+async def infer(
+    images: Optional[List[str]] = None,
+    prompt: str = "",
+    model: str = "",
+    system: str = "",
+    max_tokens: int = 1024,
+    temperature: float = 0.2,
+    timeout_s: float = 60.0,
+) -> Dict[str, Any]:
+    model = model or DEFAULT_VISION
+
+    payload: Dict[str, Any] = {
+        "model": model,
+        "prompt": prompt or "Describe this image.",
+        "max_tokens": max_tokens,
+        "temperature": temperature,
+    }
+    if images:
+        payload["images"] = images
+    if system:
+        payload["system"] = system
+
+    async with httpx.AsyncClient(timeout=timeout_s) as c:
+        resp = await c.post(f"{SWAPPER_URL}/vision", json=payload)
+        resp.raise_for_status()
+        data = resp.json()
+        return {
+            "text": data.get("text", data.get("response", "")),
+            "model": model,
+            "provider": "swapper_vision",
+        }