hub v0.23.0: host root-disk pressure monitoring + alert

New HostDiskChecker on the 60s sweep alerts the operator when a Proxmox host root
filesystem crosses warn (90%) / crit (95%). Born/persistent (a disk already full at
hub restart alerts on cycle 1); distinct host_disk_* event types from the guest disk_*;
critical band maps to severity error (the dispatcher only routes warning/error).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HxLA1mZurFq9kt8hneFeCs

hub/cmd/hub/main.go

@@ -47,6 +47,10 @@ type Config struct {
 	} `yaml:"retention"`
 	Alerting struct {
 		StaleThreshold string `yaml:"stale_threshold"`
+		// Host root-fs disk-pressure thresholds (percent). Empty/0/invalid → defaults 90/95
+		// (normalizeDiskThresholds). Seed-only config, like stale_threshold.
+		HostDiskWarnPercent float64 `yaml:"host_disk_warn_percent"`
+		HostDiskCritPercent float64 `yaml:"host_disk_crit_percent"`
 	} `yaml:"alerting"`
 	Registry struct {
 		Image            string `yaml:"image"`
@@ -322,6 +326,10 @@ func main() {
 	// agent-v0.48.0: proactive fleet-wide agent-re-key detection — alert when a host's reported
 	// local-API leaf fingerprint changes (independent of the controller channel-check). Same 60s sweep.
 	hostLeafChecker := monitor.NewHostLeafChecker(dataStore, dispatcher.ProcessEvent, logger)
+	// v0.23.0: HOST root-fs disk-pressure alert (the silent vzdump-on-root-fills class). Reads the host
+	// root disk_percent the agent reports; born/persistent (a disk already full at hub restart alerts on
+	// cycle 1). Distinct event types from the controller's GUEST disk_warning/disk_critical. Same 60s sweep.
+	hostDiskChecker := monitor.NewHostDiskChecker(dataStore, cfg.Alerting.HostDiskWarnPercent, cfg.Alerting.HostDiskCritPercent, dispatcher.ProcessEvent, logger)
 	go func() {
 		ticker := time.NewTicker(60 * time.Second)
 		defer ticker.Stop()
@@ -334,6 +342,7 @@ func main() {
 				hostStalenessChecker.Check()
 				hostCapabilityChecker.Check()
 				hostLeafChecker.Check()
+				hostDiskChecker.Check()
 			}
 		}
 	}()