### Stability Agent

A lightweight filesystem-first watchdog and observer agent for CHELSTY.

#### Features

*   **Continuous Monitoring**: Runs as a background service.
*   **Docker Inspection**: Checks container status via read-only Docker socket.
*   **Disk Usage**: Monitors local disk utilization.
*   **Tailscale Check**: Verifies Tailscale availability.
*   **MQTT Reachability**: Checks connectivity to the local MQTT broker.
*   **Zigbee2MQTT Monitoring**: Specifically monitors the Zigbee2MQTT container.
*   **Event Logging**: Writes append-only JSON events to `/opt/homelab/events/YYYY-MM-DD/chelsty/`.
*   **State Reporting**: Writes heartbeat and status summary to `/opt/homelab/state/`.

#### Configuration

Environment variables:

*   `STABILITY_CHECK_INTERVAL`: Interval between checks in seconds (default: 60).
*   `DISK_THRESHOLD_PCT`: Disk usage percentage to trigger warning (default: 90).
*   `MQTT_HOST`: Hostname or IP of the MQTT broker to check.
*   `MQTT_PORT`: Port of the MQTT broker (default: 1883).

#### Safety

*   No automatic restarts are performed.
*   Read-only access to Docker socket.
*   No configuration mutation.
*   No secrets stored in the repository.

#### Event Schema

Events are written as JSON lines with the following fields:

*   `id`: Unique event UUID.
*   `timestamp`: ISO 8601 timestamp (UTC).
*   `node`: `chelsty`.
*   `source`: `stability-agent`.
*   `type`: Type of event (e.g., `disk_usage_high`, `containers_not_running`).
*   `severity`: `info`, `warning`, or `error`.
*   `message`: Human-readable description.
*   `details`: Object containing specific check results.