Reference KVM domain disks by host path so AppArmor-confined QEMU can open them

The first run against a real hypervisor (beelink, Ubuntu, libvirt 11.6)
failed at DomainCreate with "Could not open base image: Permission denied"
even with correct DAC ownership. libvirt's virt-aa-helper only grants QEMU
access to disk sources that carry a path; the <disk type="volume"> form
chosen in Step 2 gives it pool and volume names instead, so the overlay and
its backing image get no AppArmor rule on any stock Debian/Ubuntu host.

buildDomainXML now takes DiskPath/SeedPath and emits type="file" disks.
ensureOverlay and writeSeed return the volume handles and Create resolves
both paths with StorageVolGetPath before defining the domain. The domain
XML test rejects any volume/pool reference so this cannot drift back; the
Create test asserts the sources equal the paths libvirt reported.

Execution log: Step 2 note marked reverted, Step 7 entry opened with the
two failed runs and the diagnosis.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/provider/kvm/domainxml.go

@@ -9,24 +9,29 @@ import (
 const guestAgentChannel = "org.qemu.guest_agent.0"
 
 // domainParams is everything buildDomainXML needs, already resolved from the
-// config and placement so the builder stays a pure function.
+// config and placement so the builder stays a pure function. DiskPath and
+// SeedPath are the volumes' host paths as reported by libvirt.
 type domainParams struct {
 	Name      string
 	UID       string
 	CreatedAt time.Time
 	VCPUs     int32
 	MemoryMiB int64
-	Pool      string
 	Bridge    string
-	DiskVol   string
-	SeedVol   string
+	DiskPath  string
+	SeedPath  string
 }
 
 // buildDomainXML renders a q35 KVM guest: host-passthrough CPU, a virtio
-// overlay disk and a SATA cdrom for the seed (both referenced as pool
-// volumes so no host paths are needed), one virtio NIC on the host bridge,
-// a serial console, the guest-agent channel, a virtio RNG, no graphics, and
-// the operator's metadata element.
+// overlay disk and a SATA cdrom for the seed, one virtio NIC on the host
+// bridge, a serial console, the guest-agent channel, a virtio RNG, no
+// graphics, and the operator's metadata element.
+//
+// Disks are type="file" with host paths, not type="volume" with pool/volume
+// names: libvirt's AppArmor helper (virt-aa-helper) only grants QEMU access
+// to sources that carry a path, so a volume-referenced disk fails to start
+// with "Permission denied" on any AppArmor-confined host (stock Debian and
+// Ubuntu). The paths cost one StorageVolGetPath round-trip each per Create.
 func buildDomainXML(p domainParams) (string, error) {
 	d := domainXML{
 		Type:     "kvm",
@@ -47,17 +52,17 @@ func buildDomainXML(p domainParams) (string, error) {
 		Devices: devicesXML{
 			Disks: []diskXML{
 				{
-					Type:   "volume",
+					Type:   "file",
 					Device: "disk",
 					Driver: driverXML{Name: "qemu", Type: formatQcow2},
-					Source: diskSourceXML{Pool: p.Pool, Volume: p.DiskVol},
+					Source: diskSourceXML{File: p.DiskPath},
 					Target: targetXML{Dev: "vda", Bus: "virtio"},
 				},
 				{
-					Type:     "volume",
+					Type:     "file",
 					Device:   "cdrom",
 					Driver:   driverXML{Name: "qemu", Type: formatRaw},
-					Source:   diskSourceXML{Pool: p.Pool, Volume: p.SeedVol},
+					Source:   diskSourceXML{File: p.SeedPath},
 					Target:   targetXML{Dev: "sda", Bus: "sata"},
 					ReadOnly: &struct{}{},
 				},
@@ -161,8 +166,7 @@ type driverXML struct {
 }
 
 type diskSourceXML struct {
-	Pool   string `xml:"pool,attr"`
-	Volume string `xml:"volume,attr"`
+	File string `xml:"file,attr"`
 }
 
 type targetXML struct {