Add VM (qm guest exec) cell to the Discovery scenario oracle

The corpus covered LXC and Docker workloads but not VMs, which the agent
reaches via the QEMU guest agent (qm guest exec) rather than pct/docker
exec. Add a Plex-on-VM cell — a transcode-failure question that needs the
guest-exec access, the GPU decoder (hardware fact), and the restart
command — verified through both the chat and remediation packs. Test-only
coverage; full servicediscovery package green.

internal/servicediscovery/scenario_corpus_test.go

@@ -259,6 +259,50 @@ func contextScenarioCorpus() []contextScenario {
 				"allow_anonymous false",       // security fact (now surfaced) — the connect failure
 			},
 		},
+		{
+			name:         "plex media server (VM, qm guest exec)",
+			userQuestion: "playback keeps buffering and transcodes are failing",
+			discovery: &ResourceDiscovery{
+				ID:             MakeResourceID(ResourceTypeVM, "minipc", "200"),
+				ResourceType:   ResourceTypeVM,
+				ResourceID:     "200",
+				TargetID:       "minipc",
+				Hostname:       "plex",
+				ServiceType:    "plex",
+				ServiceName:    "Plex Media Server",
+				ServiceVersion: "1.40.2",
+				Category:       CategoryMedia,
+				// VMs are reached via the QEMU guest agent, not pct/docker exec —
+				// the one resource type the other cells don't cover.
+				CLIAccess: "qm guest exec 200 -- bash",
+				ConfigPaths: []string{
+					"/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Preferences.xml",
+				},
+				DataPaths: []string{"/mnt/media"},
+				LogPaths: []string{
+					"/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Logs/Plex Media Server.log",
+				},
+				Ports: []PortInfo{{Port: 32400, Protocol: "tcp", Process: "Plex Media Server"}},
+				Facts: []DiscoveryFact{
+					{Category: FactCategoryHardware, Key: "gpu", Value: "intel-quicksync (/dev/dri/renderD128)", Source: "gpu_devices", Confidence: 0.9},
+					{Category: FactCategoryService, Key: "restart", Value: "systemctl restart plexmediaserver", Source: "running_services", Confidence: 0.9},
+				},
+			},
+			// Transcode failures point at the hardware decoder and the service: the
+			// Assistant needs how to reach the VM (qm guest exec), the GPU it should
+			// be using, and how to restart Plex.
+			mustContain: []string{
+				"qm guest exec 200",
+				"intel-quicksync",
+				"systemctl restart plexmediaserver",
+				"32400/tcp",
+			},
+			remediationMustContain: []string{
+				"systemctl restart plexmediaserver", // service control
+				"Preferences.xml",                   // config
+				"intel-quicksync",                   // hardware fact (transcode decoder)
+			},
+		},
 	}
 }