v0.310.0: „A gép kikapcsolása" — the household turns the whole machine off (R-998); honest restart text (R-999)

POST /api/server/poweroff (dashboard login, POST only, the typed word KIKAPCSOLÁS / TURN OFF)
→ agent POST /host/poweroff (MinAgent 0.155.0; hidden for an older agent). The controller refuses
during its own backup/restore/app update; the agent's reasons are shown as household sentences.
„Kiszolgáló újraindítása" becomes „A Felhom újraindítása" and says it restarts the Felhom part;
/api/server/reboot is POST only (R-983). Tests red-proofed; parity fixtures regenerated on purpose.

controller/internal/agentapi/features.go

@@ -83,6 +83,11 @@ const FeatureRecoveryFailureClass Feature = "recovery_failure_class"
 // for two months, and it heals itself when the agent updates.
 const FeatureRetainedRecoveryClass Feature = "retained_recovery_class"
 
+// FeatureHostPowerOff is the household power-off (R-998, agent v0.155.0): POST /host/poweroff. A POST that switches
+// the machine off cannot be probed, so the VERSION decides. The settings card hides only on a definite SupportNo; on
+// Unknown it stays, and an old agent's 404 is answered with the update sentence.
+const FeatureHostPowerOff Feature = "host_poweroff"
+
 // SupportState is a probe verdict. The zero value is SupportUnknown (fail-open: unknown never
 // refuses — the existing agent-error paths speak honestly when the agent is down).
 type SupportState int
@@ -159,6 +164,10 @@ var featureProbes = map[Feature]func(ctx context.Context, p SupportProber) error
 	FeatureRetainedRecoveryClass: func(ctx context.Context, p SupportProber) error {
 		return errNoRecoveryProbe
 	},
+	// R-998: probing would switch the machine off. The row must exist (table-gap rule above).
+	FeatureHostPowerOff: func(ctx context.Context, p SupportProber) error {
+		return errNoRecoveryProbe
+	},
 }
 
 // errNoMemoryProbe classifies to SupportUnknown (not a *StatusError 404), so a prober that cannot be
@@ -192,6 +201,9 @@ var featureMinAgent = map[Feature]string{
 	// screen must keep saying it cannot tell the two apart — which was true, and is what this gate
 	// preserves for boxes that have not updated yet.
 	FeatureRetainedRecoveryClass: "0.129.0",
+
+	// R-998 — POST /host/poweroff, the household's „A gép kikapcsolása".
+	FeatureHostPowerOff: "0.155.0",
 }
 
 // MinAgentFor returns the declared minimum agent version for a feature ("" when the feature has no