feat: Add chat handler with RAG pipeline

- chat_handler.py: Standalone NATS handler with RAG
- chat_handler_v2.py: Handler-base implementation
- Dockerfiles for both versions

Pipeline: Embeddings → Milvus → Rerank → LLM → (optional TTS)

.gitignore

@@ -0,0 +1,26 @@
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+build/
+dist/
+*.egg-info/
+*.egg
+
+# Virtual environments
+venv/
+.venv/
+ENV/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*~
+
+# Local
+.env
+.env.local
+*.log

Dockerfile

@@ -0,0 +1,29 @@
+FROM python:3.13-slim
+
+WORKDIR /app
+
+# Install uv for fast, reliable package management
+COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv
+
+# Install system dependencies
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    curl \
+    && rm -rf /var/lib/apt/lists/*
+
+# Copy requirements first for better caching
+COPY requirements.txt .
+RUN uv pip install --system --no-cache -r requirements.txt
+
+# Copy application code
+COPY chat_handler.py .
+
+# Set environment variables
+ENV PYTHONUNBUFFERED=1
+ENV PYTHONDONTWRITEBYTECODE=1
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
+    CMD python -c "print('healthy')" || exit 1
+
+# Run the application
+CMD ["python", "chat_handler.py"]

Dockerfile.v2

@@ -0,0 +1,11 @@
+# Chat Handler v2 - Using handler-base
+ARG BASE_TAG=local
+FROM ghcr.io/billy-davies-2/handler-base:${BASE_TAG}
+
+WORKDIR /app
+
+# Copy only the handler code (dependencies are in base image)
+COPY chat_handler_v2.py ./chat_handler.py
+
+# Run the handler
+CMD ["python", "chat_handler.py"]

README.md

@@ -1,2 +1,110 @@
-# chat-handler
+# Chat Handler
 
+Text-based chat pipeline for the DaviesTechLabs AI/ML platform.
+
+## Overview
+
+A NATS-based service that handles chat completion requests with RAG (Retrieval Augmented Generation).
+
+**Pipeline:** Query → Embeddings → Milvus → Rerank → LLM → (optional TTS)
+
+## Versions
+
+| File | Description |
+|------|-------------|
+| `chat_handler.py` | Standalone implementation (v1) |
+| `chat_handler_v2.py` | Uses handler-base library (recommended) |
+| `Dockerfile` | Standalone image |
+| `Dockerfile.v2` | Handler-base image |
+
+## Architecture
+
+```
+NATS (ai.chat.request)
+        │
+        ▼
+┌───────────────────┐
+│   Chat Handler    │
+└───────────────────┘
+        │
+        ├──▶ BGE Embeddings (drizzt)
+        │         │
+        │         ▼
+        ├──▶ Milvus Vector Search
+        │         │
+        │         ▼
+        ├──▶ BGE Reranker (danilo)
+        │         │
+        │         ▼
+        ├──▶ vLLM (khelben)
+        │         │
+        │         ▼ (optional)
+        └──▶ XTTS TTS (elminster)
+                  │
+                  ▼
+         NATS (ai.chat.response.{id})
+```
+
+## NATS Message Format
+
+### Request (ai.chat.request)
+
+```json
+{
+  "request_id": "uuid",
+  "query": "What is the capital of France?",
+  "collection": "knowledge_base",
+  "enable_tts": false,
+  "system_prompt": "Optional custom system prompt"
+}
+```
+
+### Response (ai.chat.response.{request_id})
+
+```json
+{
+  "request_id": "uuid",
+  "response": "The capital of France is Paris.",
+  "sources": [
+    {"text": "Paris is the capital...", "score": 0.95}
+  ],
+  "audio": "base64-encoded-audio (if TTS enabled)"
+}
+```
+
+## Configuration
+
+| Environment Variable | Default | Description |
+|---------------------|---------|-------------|
+| `NATS_URL` | `nats://nats.ai-ml.svc.cluster.local:4222` | NATS server |
+| `EMBEDDINGS_URL` | `http://embeddings-predictor.ai-ml.svc.cluster.local` | Embeddings |
+| `RERANKER_URL` | `http://reranker-predictor.ai-ml.svc.cluster.local` | Reranker |
+| `VLLM_URL` | `http://llm-draft.ai-ml.svc.cluster.local:8000` | LLM service |
+| `TTS_URL` | `http://tts-predictor.ai-ml.svc.cluster.local` | TTS (optional) |
+| `MILVUS_HOST` | `milvus.ai-ml.svc.cluster.local` | Vector DB |
+| `COLLECTION_NAME` | `knowledge_base` | Default Milvus collection |
+| `ENABLE_TTS` | `false` | Enable audio responses |
+
+## Building
+
+```bash
+# Standalone image (v1)
+docker build -f Dockerfile -t chat-handler:latest .
+
+# Handler-base image (v2 - recommended)
+docker build -f Dockerfile.v2 -t chat-handler:v2 .
+```
+
+## Dependencies
+
+The v2 handler depends on [handler-base](https://git.daviestechlabs.io/daviestechlabs/handler-base):
+
+```bash
+pip install git+https://git.daviestechlabs.io/daviestechlabs/handler-base.git
+```
+
+## Related
+
+- [handler-base](https://git.daviestechlabs.io/daviestechlabs/handler-base) - Base handler library
+- [voice-assistant](https://git.daviestechlabs.io/daviestechlabs/voice-assistant) - Voice pipeline
+- [homelab-design](https://git.daviestechlabs.io/daviestechlabs/homelab-design) - Architecture docs

chat_handler.py

@@ -0,0 +1,867 @@
+#!/usr/bin/env python3
+"""
+Chat Handler Service
+
+Text-based chat pipeline:
+1. Listen for text on NATS subject "ai.chat.request"
+2. Generate embeddings for RAG (optional)
+3. Retrieve context from Milvus
+4. Rerank with BGE reranker
+5. Generate response with vLLM
+6. Optionally synthesize speech with XTTS
+7. Publish result to NATS "ai.chat.response.{request_id}"
+"""
+import asyncio
+import base64
+import json
+import logging
+import os
+import signal
+import subprocess
+import sys
+import time
+from typing import List, Dict, Optional
+
+# Install dependencies on startup
+subprocess.check_call([
+    sys.executable, "-m", "pip", "install", "-q",
+    "--root-user-action=ignore",
+    "-r", "/app/requirements.txt"
+])
+
+import httpx
+import msgpack
+import nats
+import redis.asyncio as redis
+from pymilvus import connections, Collection, utility
+
+# OpenTelemetry imports
+from opentelemetry import trace, metrics
+from opentelemetry.sdk.trace import TracerProvider
+from opentelemetry.sdk.trace.export import BatchSpanProcessor
+from opentelemetry.sdk.metrics import MeterProvider
+from opentelemetry.sdk.metrics.export import PeriodicExportingMetricReader
+from opentelemetry.exporter.otlp.proto.grpc.trace_exporter import OTLPSpanExporter
+from opentelemetry.exporter.otlp.proto.grpc.metric_exporter import OTLPMetricExporter
+from opentelemetry.exporter.otlp.proto.http.trace_exporter import OTLPSpanExporter as OTLPSpanExporterHTTP
+from opentelemetry.exporter.otlp.proto.http.metric_exporter import OTLPMetricExporter as OTLPMetricExporterHTTP
+from opentelemetry.sdk.resources import Resource, SERVICE_NAME, SERVICE_VERSION, SERVICE_NAMESPACE
+from opentelemetry.instrumentation.httpx import HTTPXClientInstrumentor
+from opentelemetry.instrumentation.logging import LoggingInstrumentor
+
+# MLflow inference tracking
+try:
+    from mlflow_utils import InferenceMetricsTracker
+    from mlflow_utils.inference_tracker import InferenceMetrics
+    MLFLOW_AVAILABLE = True
+except ImportError:
+    MLFLOW_AVAILABLE = False
+    InferenceMetricsTracker = None
+    InferenceMetrics = None
+
+# Configure logging
+logging.basicConfig(
+    level=logging.INFO, format="%(asctime)s - %(name)s - %(levelname)s - %(message)s"
+)
+logger = logging.getLogger("chat-handler")
+
+
+def setup_telemetry():
+    """Initialize OpenTelemetry tracing and metrics."""
+    otel_enabled = os.environ.get("OTEL_ENABLED", "true").lower() == "true"
+    if not otel_enabled:
+        logger.info("OpenTelemetry disabled")
+        return None, None
+    
+    otel_endpoint = os.environ.get("OTEL_EXPORTER_OTLP_ENDPOINT", "http://opentelemetry-collector.observability.svc.cluster.local:4317")
+    service_name = os.environ.get("OTEL_SERVICE_NAME", "chat-handler")
+    service_namespace = os.environ.get("OTEL_SERVICE_NAMESPACE", "ai-ml")
+    
+    # HyperDX configuration
+    hyperdx_api_key = os.environ.get("HYPERDX_API_KEY", "")
+    hyperdx_endpoint = os.environ.get("HYPERDX_ENDPOINT", "https://in-otel.hyperdx.io")
+    use_hyperdx = os.environ.get("HYPERDX_ENABLED", "false").lower() == "true" and hyperdx_api_key
+    
+    resource = Resource.create({
+        SERVICE_NAME: service_name,
+        SERVICE_VERSION: os.environ.get("SERVICE_VERSION", "1.0.0"),
+        SERVICE_NAMESPACE: service_namespace,
+        "deployment.environment": os.environ.get("DEPLOYMENT_ENV", "production"),
+        "host.name": os.environ.get("HOSTNAME", "unknown"),
+    })
+    
+    trace_provider = TracerProvider(resource=resource)
+    
+    if use_hyperdx:
+        logger.info(f"Configuring HyperDX exporter at {hyperdx_endpoint}")
+        headers = {"authorization": hyperdx_api_key}
+        otlp_span_exporter = OTLPSpanExporterHTTP(
+            endpoint=f"{hyperdx_endpoint}/v1/traces",
+            headers=headers
+        )
+        otlp_metric_exporter = OTLPMetricExporterHTTP(
+            endpoint=f"{hyperdx_endpoint}/v1/metrics",
+            headers=headers
+        )
+    else:
+        otlp_span_exporter = OTLPSpanExporter(endpoint=otel_endpoint, insecure=True)
+        otlp_metric_exporter = OTLPMetricExporter(endpoint=otel_endpoint, insecure=True)
+    
+    trace_provider.add_span_processor(BatchSpanProcessor(otlp_span_exporter))
+    trace.set_tracer_provider(trace_provider)
+    
+    metric_reader = PeriodicExportingMetricReader(otlp_metric_exporter, export_interval_millis=60000)
+    meter_provider = MeterProvider(resource=resource, metric_readers=[metric_reader])
+    metrics.set_meter_provider(meter_provider)
+    
+    HTTPXClientInstrumentor().instrument()
+    LoggingInstrumentor().instrument(set_logging_format=True)
+    
+    destination = "HyperDX" if use_hyperdx else "OTEL Collector"
+    logger.info(f"OpenTelemetry initialized - destination: {destination}, service: {service_name}")
+    
+    return trace.get_tracer(__name__), metrics.get_meter(__name__)
+
+# Configuration from environment
+TTS_URL = os.environ.get("TTS_URL", "http://tts-predictor.ai-ml.svc.cluster.local")
+EMBEDDINGS_URL = os.environ.get(
+    "EMBEDDINGS_URL", "http://embeddings-predictor.ai-ml.svc.cluster.local"
+)
+RERANKER_URL = os.environ.get(
+    "RERANKER_URL", "http://reranker-predictor.ai-ml.svc.cluster.local"
+)
+VLLM_URL = os.environ.get("VLLM_URL", "http://llm-draft.ai-ml.svc.cluster.local:8000")
+LLM_MODEL = os.environ.get("LLM_MODEL", "mistralai/Mistral-7B-Instruct-v0.3")
+MILVUS_HOST = os.environ.get("MILVUS_HOST", "milvus.ai-ml.svc.cluster.local")
+MILVUS_PORT = int(os.environ.get("MILVUS_PORT", "19530"))
+COLLECTION_NAME = os.environ.get("COLLECTION_NAME", "knowledge_base")
+NATS_URL = os.environ.get("NATS_URL", "nats://nats.ai-ml.svc.cluster.local:4222")
+VALKEY_URL = os.environ.get("VALKEY_URL", "redis://valkey.ai-ml.svc.cluster.local:6379")
+
+# MLflow configuration
+MLFLOW_ENABLED = os.environ.get("MLFLOW_ENABLED", "true").lower() == "true"
+MLFLOW_TRACKING_URI = os.environ.get(
+    "MLFLOW_TRACKING_URI", "http://mlflow.mlflow.svc.cluster.local:80"
+)
+
+# Context window limits (characters)
+MAX_CONTEXT_LENGTH = int(os.environ.get("MAX_CONTEXT_LENGTH", "8000"))  # Prevent unbounded growth
+
+# NATS subjects (ai.* schema)
+# Per-user channels matching companions-frontend pattern
+REQUEST_SUBJECT = "ai.chat.user.*.message"  # Wildcard subscription for all users
+PREMIUM_REQUEST_SUBJECT = "ai.chat.premium.user.*.message"  # Premium users
+RESPONSE_SUBJECT = "ai.chat.response"  # Response published to specific request_id
+STREAM_RESPONSE_SUBJECT = "ai.chat.response.stream"  # Streaming responses (token chunks)
+
+# System prompt for the assistant
+SYSTEM_PROMPT = """You are a helpful AI assistant.
+Answer questions based on the provided context when available.
+Be concise and informative. If you don't know the answer, say so clearly."""
+
+
+class ChatHandler:
+    def __init__(self):
+        self.nc = None
+        self.http_client = None
+        self.collection = None
+        self.valkey_client = None
+        self.running = True
+        self.tracer = None
+        self.meter = None
+        self.request_counter = None
+        self.request_duration = None
+        self.rag_search_duration = None
+        # MLflow inference tracker
+        self.mlflow_tracker = None
+
+    async def setup(self):
+        """Initialize all connections."""
+        # Initialize OpenTelemetry
+        self.tracer, self.meter = setup_telemetry()
+        
+        # Setup metrics
+        if self.meter:
+            self.request_counter = self.meter.create_counter(
+                "chat.requests",
+                description="Number of chat requests processed",
+                unit="1"
+            )
+            self.request_duration = self.meter.create_histogram(
+                "chat.request_duration",
+                description="Duration of chat request processing",
+                unit="s"
+            )
+            self.rag_search_duration = self.meter.create_histogram(
+                "chat.rag_search_duration",
+                description="Duration of RAG search operations",
+                unit="s"
+            )
+        
+        # Initialize MLflow inference tracker
+        if MLFLOW_ENABLED and MLFLOW_AVAILABLE:
+            try:
+                self.mlflow_tracker = InferenceMetricsTracker(
+                    service_name="chat-handler",
+                    experiment_name="chat-inference",
+                    tracking_uri=MLFLOW_TRACKING_URI,
+                    batch_size=50,
+                    flush_interval_seconds=60.0,
+                )
+                await self.mlflow_tracker.start()
+                logger.info(f"MLflow inference tracking enabled at {MLFLOW_TRACKING_URI}")
+            except Exception as e:
+                logger.warning(f"MLflow initialization failed: {e}, tracking disabled")
+                self.mlflow_tracker = None
+        elif not MLFLOW_AVAILABLE:
+            logger.info("MLflow utils not available, inference tracking disabled")
+        else:
+            logger.info("MLflow tracking disabled via MLFLOW_ENABLED=false")
+        
+        # NATS connection with reconnection support
+        async def disconnected_cb():
+            logger.warning("NATS disconnected, attempting reconnection...")
+        
+        async def reconnected_cb():
+            logger.info(f"NATS reconnected to {self.nc.connected_url.netloc}")
+        
+        async def error_cb(e):
+            logger.error(f"NATS error: {e}")
+        
+        async def closed_cb():
+            logger.warning("NATS connection closed")
+        
+        self.nc = await nats.connect(
+            NATS_URL,
+            reconnect_time_wait=2,
+            max_reconnect_attempts=-1,  # Infinite reconnection attempts
+            disconnected_cb=disconnected_cb,
+            reconnected_cb=reconnected_cb,
+            error_cb=error_cb,
+            closed_cb=closed_cb,
+        )
+        logger.info(f"Connected to NATS at {NATS_URL}")
+
+        # HTTP client for services
+        self.http_client = httpx.AsyncClient(timeout=180.0)
+
+        # Connect to Valkey for conversation history and context caching
+        try:
+            self.valkey_client = redis.from_url(
+                VALKEY_URL,
+                encoding="utf-8",
+                decode_responses=True,
+                socket_connect_timeout=5
+            )
+            await self.valkey_client.ping()
+            logger.info(f"Connected to Valkey at {VALKEY_URL}")
+        except Exception as e:
+            logger.warning(f"Valkey connection failed: {e}, conversation history disabled")
+            self.valkey_client = None
+
+        # Connect to Milvus if collection exists
+        try:
+            connections.connect(host=MILVUS_HOST, port=MILVUS_PORT)
+            if utility.has_collection(COLLECTION_NAME):
+                self.collection = Collection(COLLECTION_NAME)
+                self.collection.load()
+                logger.info(f"Connected to Milvus collection: {COLLECTION_NAME}")
+            else:
+                logger.warning(f"Collection {COLLECTION_NAME} not found, RAG disabled")
+        except Exception as e:
+            logger.warning(f"Milvus connection failed: {e}, RAG disabled")
+
+    async def get_embeddings(self, texts: List[str]) -> List[List[float]]:
+        """Get embeddings from the embedding service."""
+        try:
+            response = await self.http_client.post(
+                f"{EMBEDDINGS_URL}/embeddings", json={"input": texts, "model": "bge"}
+            )
+            result = response.json()
+            return [d["embedding"] for d in result.get("data", [])]
+        except Exception as e:
+            logger.error(f"Embedding failed: {e}")
+            return []
+
+    async def search_milvus(
+        self, query_embedding: List[float], top_k: int = 5
+    ) -> List[Dict]:
+        """Search Milvus for relevant documents."""
+        if not self.collection:
+            return []
+        try:
+            results = self.collection.search(
+                data=[query_embedding],
+                anns_field="embedding",
+                param={"metric_type": "COSINE", "params": {"ef": 64}},
+                limit=top_k,
+                output_fields=["text", "book_name", "page_num"],
+            )
+            docs = []
+            for hits in results:
+                for hit in hits:
+                    docs.append(
+                        {
+                            "text": hit.entity.get("text", ""),
+                            "source": f'{hit.entity.get("book_name", "")} p.{hit.entity.get("page_num", "")}',
+                            "score": hit.score,
+                        }
+                    )
+            return docs
+        except Exception as e:
+            logger.error(f"Milvus search failed: {e}")
+            return []
+
+    async def rerank(self, query: str, documents: List[str]) -> List[Dict]:
+        """Rerank documents using the reranker service."""
+        if not documents:
+            return []
+        try:
+            response = await self.http_client.post(
+                f"{RERANKER_URL}/v1/rerank",
+                json={"query": query, "documents": documents},
+            )
+            return response.json().get("results", [])
+        except Exception as e:
+            logger.error(f"Reranking failed: {e}")
+            return [{"index": i, "relevance_score": 0.5} for i in range(len(documents))]
+
+    async def get_conversation_history(self, session_id: str, max_messages: int = 10) -> List[Dict]:
+        """Retrieve conversation history from Valkey."""
+        if not self.valkey_client or not session_id:
+            return []
+        try:
+            key = f"chat:history:{session_id}"
+            # Get the most recent messages (stored as a list)
+            history_json = await self.valkey_client.lrange(key, -max_messages, -1)
+            history = [json.loads(msg) for msg in history_json]
+            logger.info(f"Retrieved {len(history)} messages from history for session {session_id}")
+            return history
+        except Exception as e:
+            logger.error(f"Failed to get conversation history: {e}")
+            return []
+
+    async def save_message_to_history(self, session_id: str, role: str, content: str, ttl: int = 3600):
+        """Save a message to conversation history in Valkey."""
+        if not self.valkey_client or not session_id:
+            return
+        try:
+            key = f"chat:history:{session_id}"
+            message = json.dumps({"role": role, "content": content, "timestamp": time.time()})
+            # Use RPUSH to append to the list
+            await self.valkey_client.rpush(key, message)
+            # Set TTL on the key (1 hour by default)
+            await self.valkey_client.expire(key, ttl)
+            logger.debug(f"Saved {role} message to history for session {session_id}")
+        except Exception as e:
+            logger.error(f"Failed to save message to history: {e}")
+
+    async def get_context_window(self, session_id: str) -> Optional[str]:
+        """Retrieve cached context window from Valkey for attention offloading."""
+        if not self.valkey_client or not session_id:
+            return None
+        try:
+            key = f"chat:context:{session_id}"
+            context = await self.valkey_client.get(key)
+            if context:
+                logger.info(f"Retrieved cached context window for session {session_id}")
+            return context
+        except Exception as e:
+            logger.error(f"Failed to get context window: {e}")
+            return None
+
+    async def save_context_window(self, session_id: str, context: str, ttl: int = 3600):
+        """Save context window to Valkey for attention offloading."""
+        if not self.valkey_client or not session_id:
+            return
+        try:
+            key = f"chat:context:{session_id}"
+            await self.valkey_client.set(key, context, ex=ttl)
+            logger.debug(f"Saved context window for session {session_id}")
+        except Exception as e:
+            logger.error(f"Failed to save context window: {e}")
+
+    async def generate_response(self, query: str, context: str = "", session_id: str = None) -> str:
+        """Generate response using vLLM with conversation history from Valkey."""
+        try:
+            messages = [{"role": "system", "content": SYSTEM_PROMPT}]
+            
+            # Add conversation history from Valkey if session exists
+            if session_id:
+                history = await self.get_conversation_history(session_id)
+                messages.extend(history)
+            
+            if context:
+                messages.append(
+                    {
+                        "role": "user",
+                        "content": f"Context:\n{context}\n\nQuestion: {query}",
+                    }
+                )
+            else:
+                messages.append({"role": "user", "content": query})
+
+            response = await self.http_client.post(
+                f"{VLLM_URL}/v1/chat/completions",
+                json={
+                    "model": LLM_MODEL,
+                    "messages": messages,
+                    "max_tokens": 1000,
+                    "temperature": 0.7,
+                },
+            )
+            result = response.json()
+            answer = result["choices"][0]["message"]["content"]
+            logger.info(f"Generated response: {answer[:100]}...")
+            
+            # Save messages to conversation history
+            if session_id:
+                await self.save_message_to_history(session_id, "user", query)
+                await self.save_message_to_history(session_id, "assistant", answer)
+            
+            return answer
+        except Exception as e:
+            logger.error(f"LLM generation failed: {e}")
+            return "I'm sorry, I couldn't generate a response."
+
+    async def generate_response_streaming(self, query: str, context: str = "", request_id: str = "", session_id: str = None):
+        """Generate streaming response using vLLM and publish chunks to NATS.
+        
+        Yields tokens as they are generated and publishes them to NATS streaming subject.
+        Returns the complete response text.
+        """
+        try:
+            messages = [{"role": "system", "content": SYSTEM_PROMPT}]
+            
+            # Add conversation history from Valkey if session exists
+            if session_id:
+                history = await self.get_conversation_history(session_id)
+                messages.extend(history)
+            
+            if context:
+                messages.append(
+                    {
+                        "role": "user",
+                        "content": f"Context:\n{context}\n\nQuestion: {query}",
+                    }
+                )
+            else:
+                messages.append({"role": "user", "content": query})
+
+            full_response = ""
+            
+            # Stream response from vLLM
+            async with self.http_client.stream(
+                "POST",
+                f"{VLLM_URL}/v1/chat/completions",
+                json={
+                    "model": LLM_MODEL,
+                    "messages": messages,
+                    "max_tokens": 1000,
+                    "temperature": 0.7,
+                    "stream": True,
+                },
+                timeout=60.0,
+            ) as response:
+                # Parse SSE (Server-Sent Events) stream
+                async for line in response.aiter_lines():
+                    if not line or not line.startswith("data: "):
+                        continue
+                    
+                    data_str = line[6:]  # Remove "data: " prefix
+                    if data_str.strip() == "[DONE]":
+                        break
+                    
+                    try:
+                        chunk_data = json.loads(data_str)
+                        
+                        # Extract token from delta
+                        if chunk_data.get("choices") and len(chunk_data["choices"]) > 0:
+                            delta = chunk_data["choices"][0].get("delta", {})
+                            content = delta.get("content", "")
+                            
+                            if content:
+                                full_response += content
+                                
+                                # Publish token chunk to NATS streaming subject
+                                chunk_msg = {
+                                    "request_id": request_id,
+                                    "type": "chunk",
+                                    "content": content,
+                                    "done": False,
+                                }
+                                await self.nc.publish(
+                                    f"{STREAM_RESPONSE_SUBJECT}.{request_id}",
+                                    msgpack.packb(chunk_msg)
+                                )
+                    except json.JSONDecodeError:
+                        continue
+            
+            # Send completion message
+            completion_msg = {
+                "request_id": request_id,
+                "type": "done",
+                "content": "",
+                "done": True,
+            }
+            await self.nc.publish(
+                f"{STREAM_RESPONSE_SUBJECT}.{request_id}",
+                msgpack.packb(completion_msg)
+            )
+            
+            logger.info(f"Streamed complete response ({len(full_response)} chars) for request {request_id}")
+            
+            # Save messages to conversation history
+            if session_id:
+                await self.save_message_to_history(session_id, "user", query)
+                await self.save_message_to_history(session_id, "assistant", full_response)
+            
+            return full_response
+            
+        except Exception as e:
+            logger.error(f"Streaming LLM generation failed: {e}")
+            # Send error message
+            error_msg = {
+                "request_id": request_id,
+                "type": "error",
+                "content": "I'm sorry, I couldn't generate a response.",
+                "done": True,
+                "error": str(e),
+            }
+            await self.nc.publish(
+                f"{STREAM_RESPONSE_SUBJECT}.{request_id}",
+                msgpack.packb(error_msg)
+            )
+            return "I'm sorry, I couldn't generate a response."
+
+    async def synthesize_speech(self, text: str, language: str = "en") -> str:
+        """Convert text to speech using XTTS (Coqui TTS)."""
+        try:
+            response = await self.http_client.get(
+                f"{TTS_URL}/api/tts", params={"text": text, "language_id": language}
+            )
+            if response.status_code == 200:
+                audio_b64 = base64.b64encode(response.content).decode("utf-8")
+                logger.info(f"Synthesized {len(response.content)} bytes of audio")
+                return audio_b64
+            else:
+                logger.error(
+                    f"TTS returned status {response.status_code}: {response.text}"
+                )
+                return ""
+        except Exception as e:
+            logger.error(f"TTS failed: {e}")
+            return ""
+
+    async def process_request(self, msg, is_premium=False):
+        """Process a chat request."""
+        start_time = time.time()
+        span = None
+        
+        # MLflow metrics tracking
+        mlflow_metrics = None
+        embedding_start = None
+        rag_start = None
+        rerank_start = None
+        llm_start = None
+        
+        try:
+            data = msgpack.unpackb(msg.data, raw=False)
+            
+            # Support companions-frontend format (user_id, username, message, premium)
+            # as well as the original format (request_id, text, enable_rag, etc.)
+            user_id = data.get("user_id")
+            username = data.get("username", "")
+            
+            # Get text from either 'message' (companions-frontend) or 'text' (original)
+            text = data.get("message") or data.get("text", "")
+            
+            # Generate request_id from user_id if not provided
+            import uuid
+            request_id = data.get("request_id") or f"{user_id or 'anon'}-{uuid.uuid4().hex[:8]}"
+            
+            # Initialize MLflow metrics if available
+            if self.mlflow_tracker and MLFLOW_AVAILABLE:
+                mlflow_metrics = InferenceMetrics(
+                    request_id=request_id,
+                    user_id=user_id,
+                    session_id=data.get("session_id"),
+                    model_name=LLM_MODEL,
+                    model_endpoint=VLLM_URL,
+                )
+            
+            # Start tracing span
+            if self.tracer:
+                span = self.tracer.start_span("chat.process_request")
+                span.set_attribute("request_id", request_id)
+                span.set_attribute("user_id", user_id or "anonymous")
+                span.set_attribute("premium", is_premium)
+            
+            # Premium status from message or channel
+            is_premium = is_premium or data.get("premium", False)
+
+            # Support both new parameters and backward compatibility with use_rag
+            use_rag = data.get("use_rag")  # Legacy parameter
+            enable_rag = data.get(
+                "enable_rag", use_rag if use_rag is not None else True
+            )
+            enable_reranker = data.get(
+                "enable_reranker", use_rag if use_rag is not None else True
+            )
+
+            # Premium users get more documents for deeper RAG
+            default_top_k = 15 if is_premium else 5
+            top_k = data.get("top_k", default_top_k)
+
+            # Get request parameters
+            enable_tts = data.get("enable_tts", False)
+            enable_streaming = data.get("enable_streaming", False)  # New parameter for streaming
+            language = data.get("language", "en")
+            session_id = data.get("session_id")
+            
+            # Update MLflow metrics with request params
+            if mlflow_metrics:
+                mlflow_metrics.rag_enabled = enable_rag
+                mlflow_metrics.reranker_enabled = enable_reranker
+                mlflow_metrics.is_streaming = enable_streaming
+                mlflow_metrics.is_premium = is_premium
+                mlflow_metrics.prompt_length = len(text)
+            
+            # Add attributes to span
+            if span:
+                span.set_attribute("enable_rag", enable_rag)
+                span.set_attribute("enable_reranker", enable_reranker)
+                span.set_attribute("top_k", top_k)
+                span.set_attribute("enable_tts", enable_tts)
+                span.set_attribute("enable_streaming", enable_streaming)
+
+            logger.info(
+                f"Processing {'premium ' if is_premium else ''}chat request {request_id} from {username or user_id or 'anonymous'}: {text[:50]}... (RAG: {enable_rag}, Reranker: {enable_reranker}, top_k: {top_k})"
+            )
+
+            # Warn if reranker is enabled without RAG
+            if enable_reranker and not enable_rag:
+                logger.warning(
+                    f"Request {request_id}: Reranker enabled without RAG - no documents to rerank"
+                )
+
+            if not text:
+                await self.publish_error(request_id, "No text provided")
+                return
+
+            context = ""
+            rag_sources = []
+            docs = []
+
+            # Step 1: RAG retrieval (if enabled)
+            if enable_rag and self.collection:
+                # Get embeddings for RAG
+                embedding_start = time.time()
+                embeddings = await self.get_embeddings([text])
+                if mlflow_metrics:
+                    mlflow_metrics.embedding_latency = time.time() - embedding_start
+                
+                if embeddings:
+                    # Search Milvus with configurable top_k
+                    rag_start = time.time()
+                    docs = await self.search_milvus(embeddings[0], top_k=top_k)
+                    if mlflow_metrics:
+                        mlflow_metrics.rag_search_latency = time.time() - rag_start
+                        mlflow_metrics.rag_documents_retrieved = len(docs)
+                    if docs:
+                        rag_sources = [d.get("source", "") for d in docs]
+
+            # Step 2: Reranking (if enabled and we have documents)
+            if enable_reranker and docs:
+                # Rerank documents
+                rerank_start = time.time()
+                doc_texts = [d["text"] for d in docs]
+                reranked = await self.rerank(text, doc_texts)
+                if mlflow_metrics:
+                    mlflow_metrics.rerank_latency = time.time() - rerank_start
+                # Take top 3 reranked documents with bounds checking
+                sorted_docs = sorted(
+                    reranked, key=lambda x: x.get("relevance_score", 0), reverse=True
+                )[:3]
+                # Build context with bounds checking
+                # Note: doc_texts and docs have the same length (doc_texts derived from docs)
+                context_parts = []
+                sources = []
+                for item in sorted_docs:
+                    idx = item.get("index", -1)
+                    if 0 <= idx < len(docs):
+                        context_parts.append(doc_texts[idx])
+                        sources.append(docs[idx].get("source", ""))
+                    else:
+                        logger.warning(
+                            f"Reranker returned invalid index {idx} for {len(docs)} docs"
+                        )
+                context = "\n\n".join(context_parts)
+                rag_sources = sources
+            elif docs:
+                # Use documents without reranking (take top 3)
+                doc_texts = [d["text"] for d in docs[:3]]
+                context = "\n\n".join(doc_texts)
+                rag_sources = [d.get("source", "") for d in docs[:3]]
+
+            # Step 3: Generate response (streaming or non-streaming)
+            # Check for cached context window from Valkey (for attention offloading)
+            cached_context = None
+            if session_id:
+                cached_context = await self.get_context_window(session_id)
+            
+            # Combine RAG context with cached context if available
+            if cached_context and context:
+                # Prepend cached context to current RAG context
+                combined_context = f"{cached_context}\n\n{context}"
+                # Truncate to prevent unbounded growth
+                if len(combined_context) > MAX_CONTEXT_LENGTH:
+                    logger.warning(f"Context length {len(combined_context)} exceeds max {MAX_CONTEXT_LENGTH}, truncating")
+                    # Keep the most recent context (from the end)
+                    combined_context = combined_context[-MAX_CONTEXT_LENGTH:]
+                context = combined_context
+            elif cached_context:
+                # Only cached context, still need to check length
+                if len(cached_context) > MAX_CONTEXT_LENGTH:
+                    logger.warning(f"Cached context length {len(cached_context)} exceeds max {MAX_CONTEXT_LENGTH}, truncating")
+                    cached_context = cached_context[-MAX_CONTEXT_LENGTH:]
+                context = cached_context
+            
+            # Save the combined context for future use (already truncated if needed)
+            if session_id and context:
+                await self.save_context_window(session_id, context)
+            
+            # Track number of RAG docs used after reranking
+            if mlflow_metrics and enable_rag:
+                mlflow_metrics.rag_documents_used = min(3, len(docs)) if docs else 0
+            
+            llm_start = time.time()
+            if enable_streaming:
+                # Use streaming response
+                answer = await self.generate_response_streaming(text, context, request_id, session_id)
+            else:
+                # Use non-streaming response
+                answer = await self.generate_response(text, context, session_id)
+            
+            if mlflow_metrics:
+                mlflow_metrics.llm_latency = time.time() - llm_start
+                mlflow_metrics.response_length = len(answer)
+                # Estimate token counts (rough approximation: 4 chars per token)
+                mlflow_metrics.input_tokens = len(text) // 4
+                mlflow_metrics.output_tokens = len(answer) // 4
+                mlflow_metrics.total_tokens = mlflow_metrics.input_tokens + mlflow_metrics.output_tokens
+
+            # Step 4: Optionally synthesize speech
+            audio_b64 = ""
+            if enable_tts:
+                audio_b64 = await self.synthesize_speech(answer, language)
+
+            # Publish result
+            # Include both 'response' (companions-frontend) and 'response_text' (original) for compatibility
+            result = {
+                "request_id": request_id,
+                "user_id": user_id,
+                "text": text,
+                "response": answer,  # companions-frontend expects 'response'
+                "response_text": answer,  # original format
+                "audio_b64": audio_b64 if enable_tts else None,
+                "used_rag": bool(context),
+                "rag_enabled": enable_rag,
+                "reranker_enabled": enable_reranker,
+                "rag_sources": rag_sources,
+                "session_id": session_id,
+                "success": True,
+            }
+            await self.nc.publish(
+                f"{RESPONSE_SUBJECT}.{request_id}", msgpack.packb(result)
+            )
+            logger.info(f"Published response for request {request_id}")
+            
+            # Record metrics
+            duration = time.time() - start_time
+            if self.request_counter:
+                self.request_counter.add(1, {"premium": str(is_premium), "rag_enabled": str(enable_rag), "success": "true"})
+            if self.request_duration:
+                self.request_duration.record(duration, {"premium": str(is_premium), "rag_enabled": str(enable_rag)})
+            if span:
+                span.set_attribute("success", True)
+                span.set_attribute("response_length", len(answer))
+            
+            # Log to MLflow
+            if self.mlflow_tracker and mlflow_metrics:
+                mlflow_metrics.total_latency = duration
+                await self.mlflow_tracker.log_inference(mlflow_metrics)
+
+        except Exception as e:
+            logger.error(f"Request processing failed: {e}")
+            if self.request_counter:
+                self.request_counter.add(1, {"premium": str(is_premium), "success": "false"})
+            if span:
+                span.set_attribute("success", False)
+                span.set_attribute("error", str(e))
+            
+            # Log error to MLflow
+            if self.mlflow_tracker and mlflow_metrics:
+                mlflow_metrics.has_error = True
+                mlflow_metrics.error_message = str(e)
+                mlflow_metrics.total_latency = time.time() - start_time
+                await self.mlflow_tracker.log_inference(mlflow_metrics)
+            
+            await self.publish_error(data.get("request_id", "unknown"), str(e))
+        finally:
+            if span:
+                span.end()
+
+    async def publish_error(self, request_id: str, error: str):
+        """Publish an error response."""
+        result = {"request_id": request_id, "error": error, "success": False}
+        await self.nc.publish(
+            f"{RESPONSE_SUBJECT}.{request_id}", msgpack.packb(result)
+        )
+
+    async def process_premium_request(self, msg):
+        """Process a premium chat request (wrapper for deeper RAG)."""
+        await self.process_request(msg, is_premium=True)
+
+    async def run(self):
+        """Main run loop."""
+        await self.setup()
+
+        # Subscribe to standard chat requests
+        sub = await self.nc.subscribe(REQUEST_SUBJECT, cb=self.process_request)
+        logger.info(f"Subscribed to {REQUEST_SUBJECT}")
+
+        # Subscribe to premium chat requests (deeper RAG retrieval)
+        premium_sub = await self.nc.subscribe(
+            PREMIUM_REQUEST_SUBJECT, cb=self.process_premium_request
+        )
+        logger.info(f"Subscribed to {PREMIUM_REQUEST_SUBJECT}")
+
+        # Handle shutdown
+        def signal_handler():
+            self.running = False
+
+        loop = asyncio.get_event_loop()
+        for sig in (signal.SIGTERM, signal.SIGINT):
+            loop.add_signal_handler(sig, signal_handler)
+
+        # Keep running
+        while self.running:
+            await asyncio.sleep(1)
+
+        # Cleanup
+        await sub.unsubscribe()
+        await premium_sub.unsubscribe()
+        await self.nc.close()
+        if self.valkey_client:
+            await self.valkey_client.close()
+        if self.collection:
+            connections.disconnect("default")
+        if self.mlflow_tracker:
+            await self.mlflow_tracker.stop()
+        logger.info("Shutdown complete")
+
+
+if __name__ == "__main__":
+    handler = ChatHandler()
+    asyncio.run(handler.run())

chat_handler_v2.py

@@ -0,0 +1,233 @@
+#!/usr/bin/env python3
+"""
+Chat Handler Service (Refactored)
+
+Text-based chat pipeline using handler-base:
+1. Listen for text on NATS subject "ai.chat.request"
+2. Generate embeddings for RAG
+3. Retrieve context from Milvus
+4. Rerank with BGE reranker
+5. Generate response with vLLM
+6. Optionally synthesize speech with XTTS
+7. Publish result to NATS "ai.chat.response.{request_id}"
+"""
+import base64
+import logging
+from typing import Any, Optional
+
+from nats.aio.msg import Msg
+
+from handler_base import Handler, Settings
+from handler_base.clients import (
+    EmbeddingsClient,
+    RerankerClient,
+    LLMClient,
+    TTSClient,
+    MilvusClient,
+)
+from handler_base.telemetry import create_span
+
+logger = logging.getLogger("chat-handler")
+
+
+class ChatSettings(Settings):
+    """Chat handler specific settings."""
+    
+    service_name: str = "chat-handler"
+    
+    # RAG settings
+    rag_top_k: int = 10
+    rag_rerank_top_k: int = 5
+    rag_collection: str = "documents"
+    
+    # Response settings
+    include_sources: bool = True
+    enable_tts: bool = False
+    tts_language: str = "en"
+
+
+class ChatHandler(Handler):
+    """
+    Chat request handler with RAG pipeline.
+    
+    Request format:
+    {
+        "request_id": "uuid",
+        "query": "user question",
+        "collection": "optional collection name",
+        "enable_tts": false,
+        "system_prompt": "optional custom system prompt"
+    }
+    
+    Response format:
+    {
+        "request_id": "uuid",
+        "response": "generated response",
+        "sources": [{"text": "...", "score": 0.95}],
+        "audio": "base64 encoded audio (if tts enabled)"
+    }
+    """
+    
+    def __init__(self):
+        self.chat_settings = ChatSettings()
+        super().__init__(
+            subject="ai.chat.request",
+            settings=self.chat_settings,
+            queue_group="chat-handlers",
+        )
+    
+    async def setup(self) -> None:
+        """Initialize service clients."""
+        logger.info("Initializing service clients...")
+        
+        self.embeddings = EmbeddingsClient(self.chat_settings)
+        self.reranker = RerankerClient(self.chat_settings)
+        self.llm = LLMClient(self.chat_settings)
+        self.milvus = MilvusClient(self.chat_settings)
+        
+        # TTS is optional
+        if self.chat_settings.enable_tts:
+            self.tts = TTSClient(self.chat_settings)
+        else:
+            self.tts = None
+        
+        # Connect to Milvus
+        await self.milvus.connect(self.chat_settings.rag_collection)
+        
+        logger.info("Service clients initialized")
+    
+    async def teardown(self) -> None:
+        """Clean up service clients."""
+        logger.info("Closing service clients...")
+        
+        await self.embeddings.close()
+        await self.reranker.close()
+        await self.llm.close()
+        await self.milvus.close()
+        
+        if self.tts:
+            await self.tts.close()
+        
+        logger.info("Service clients closed")
+    
+    async def handle_message(self, msg: Msg, data: Any) -> Optional[dict]:
+        """Handle incoming chat request."""
+        request_id = data.get("request_id", "unknown")
+        query = data.get("query", "")
+        collection = data.get("collection", self.chat_settings.rag_collection)
+        enable_tts = data.get("enable_tts", self.chat_settings.enable_tts)
+        system_prompt = data.get("system_prompt")
+        
+        logger.info(f"Processing request {request_id}: {query[:50]}...")
+        
+        with create_span("chat.process") as span:
+            if span:
+                span.set_attribute("request.id", request_id)
+                span.set_attribute("query.length", len(query))
+            
+            # 1. Generate query embedding
+            embedding = await self._get_embedding(query)
+            
+            # 2. Search Milvus for context
+            documents = await self._search_context(embedding, collection)
+            
+            # 3. Rerank documents
+            reranked = await self._rerank_documents(query, documents)
+            
+            # 4. Build context from top documents
+            context = self._build_context(reranked)
+            
+            # 5. Generate LLM response
+            response_text = await self._generate_response(
+                query, context, system_prompt
+            )
+            
+            # 6. Optionally synthesize speech
+            audio_b64 = None
+            if enable_tts and self.tts:
+                audio_b64 = await self._synthesize_speech(response_text)
+            
+            # Build response
+            result = {
+                "request_id": request_id,
+                "response": response_text,
+            }
+            
+            if self.chat_settings.include_sources:
+                result["sources"] = [
+                    {"text": d["document"][:200], "score": d["score"]}
+                    for d in reranked[:3]
+                ]
+            
+            if audio_b64:
+                result["audio"] = audio_b64
+            
+            logger.info(f"Completed request {request_id}")
+            
+            # Publish to response subject
+            response_subject = f"ai.chat.response.{request_id}"
+            await self.nats.publish(response_subject, result)
+            
+            return result
+    
+    async def _get_embedding(self, text: str) -> list[float]:
+        """Generate embedding for query text."""
+        with create_span("chat.embedding"):
+            return await self.embeddings.embed_single(text)
+    
+    async def _search_context(
+        self, embedding: list[float], collection: str
+    ) -> list[dict]:
+        """Search Milvus for relevant documents."""
+        with create_span("chat.search"):
+            return await self.milvus.search_with_texts(
+                embedding,
+                limit=self.chat_settings.rag_top_k,
+                text_field="text",
+                metadata_fields=["source", "title"],
+            )
+    
+    async def _rerank_documents(
+        self, query: str, documents: list[dict]
+    ) -> list[dict]:
+        """Rerank documents by relevance to query."""
+        with create_span("chat.rerank"):
+            texts = [d.get("text", "") for d in documents]
+            return await self.reranker.rerank(
+                query, texts, top_k=self.chat_settings.rag_rerank_top_k
+            )
+    
+    def _build_context(self, documents: list[dict]) -> str:
+        """Build context string from ranked documents."""
+        context_parts = []
+        for i, doc in enumerate(documents, 1):
+            text = doc.get("document", "")
+            context_parts.append(f"[{i}] {text}")
+        return "\n\n".join(context_parts)
+    
+    async def _generate_response(
+        self,
+        query: str,
+        context: str,
+        system_prompt: Optional[str] = None,
+    ) -> str:
+        """Generate LLM response with context."""
+        with create_span("chat.generate"):
+            return await self.llm.generate(
+                query,
+                context=context,
+                system_prompt=system_prompt,
+            )
+    
+    async def _synthesize_speech(self, text: str) -> str:
+        """Synthesize speech and return base64 encoded audio."""
+        with create_span("chat.tts"):
+            audio_bytes = await self.tts.synthesize(
+                text,
+                language=self.chat_settings.tts_language,
+            )
+            return base64.b64encode(audio_bytes).decode()
+
+
+if __name__ == "__main__":
+    ChatHandler().run()

requirements.txt

@@ -0,0 +1,15 @@
+nats-py
+httpx
+pymilvus
+numpy
+msgpack
+redis>=5.0.0
+opentelemetry-api
+opentelemetry-sdk
+opentelemetry-exporter-otlp-proto-grpc
+opentelemetry-exporter-otlp-proto-http
+opentelemetry-instrumentation-httpx
+opentelemetry-instrumentation-logging
+# MLflow for inference metrics tracking
+mlflow>=2.10.0
+psycopg2-binary>=2.9.0