feat(agent): change detection + webhook/syslog alerts (P2-02 / 26.13)#16
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The agent now diffs the host inventory pre- and post-cycle and emits host.discovered / host.vanished events to configurable sinks. Operators no longer have to tail logs to notice a new device. New package internal/alerts: - Event + EventType (host.discovered, host.vanished). JSON-tagged for wire reuse. - Emitter interface + Multiplexer that fans events out to N sinks in parallel goroutines. Sink failures log but don't suppress sibling deliveries. - WebhookSink: HTTP POST JSON, one retry on 5xx/network, no retry on 4xx, optional Authorization header. - SyslogSink: RFC 5424 over UDP/TCP, hand-rolled because log/syslog is Unix-only and the agent runs on Windows. Message body is the same JSON as the webhook payload, so structured syslog parsers get fields for free. - NoopEmitter for the alerts-disabled default. Config gains an optional "alerts" section with webhook and syslog sub-sections. Either or both may be set. agent.New takes a new Emitter parameter (nil = noop). runCycle snapshots hosts pre-scan, snapshots again post-prune, and diffs by IP. Discovered events get fresh enrichment; vanished events get the last-known pre-cycle row. Cycle-failed runs skip the diff to avoid alert spam on transient DB errors. 11 new tests: multiplexer fan-out, sibling-survives-peer-error, webhook auth-header round-trip, 5xx retry, 4xx no-retry, nil-on- empty guards, syslog RFC 5424 format check against a real UDP listener (PRI math, MSGID, JSON MSG), bad-scheme rejection, end-to-end discovered+vanished events from the agent. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
The agent now diffs the host inventory before and after every scan cycle and fires `host.discovered` / `host.vanished` events to configurable sinks. Operators no longer have to tail logs to notice a new device.
```json
{
"alerts": {
"webhook": { "url": "https://hooks.example/x\", "auth_header": "Bearer abc" },
"syslog": { "addr": "udp://syslog.example:514", "tag": "inventory" }
}
}
```
Both sinks ship the same JSON payload (`{type, ip, hostname, mac_address, vendor, device_type, time, agent}`). The syslog sink wraps it in RFC 5424; `rsyslog mmjsonparse` / `syslog-ng` / Splunk all parse out the inner fields for free.
Why two sinks
Operators pick one or both. Empty config disables alerting (no change for existing deployments).
Reliability model
Test plan
🤖 Generated with Claude Code