# 006 — Health Checks: Active Probes for PubSub and DHT

- Area: `main.go`, `pkg/health/*`, `pubsub/*`, `pkg/dht/*`
- Priority: Medium

## Background
Health checks for PubSub and DHT currently return static "healthy" messages. They should perform live probes to detect real outages.

## Scope / Deliverables
- PubSub check: publish a transient message to a loopback test topic and await receipt within timeout.
- DHT check: put/get a small test value under a temporary key; measure latency.
- Include metrics (latency, last success time) in health details.

## Acceptance Criteria / Tests
- When pubsub or DHT is down, health check reports unhealthy with reason.
- When restored, checks turn healthy and update timestamps.

## Notes
- Keep probe frequency/configurable to avoid noise.

