parity: add LCOW document permutation tests

Add TestLCOWDocumentParityPermutations to exercise annotation and option
combinations that trigger different document construction branches in the
legacy and v2 LCOW pipelines. Each test sets all required fields so
comparisons check real values rather than defaults.

Permutation categories:
- CPU partial combinations (count, limit, weight)
- Memory (overcommit disabled, cold discard hint)
- Boot mode (kernel direct + VHD rootfs)
- Feature flags (scratch encryption, writable overlay)
- Device interactions (VPMem disabled → 4 SCSI controllers)
- Cross-group (physically backed + VPMem + encryption)
- Shim option overrides (annotation CPU/memory priority)
- Kernel args (VPCIEnabled, time sync, process dump, initrd boot)

Gap tests document three known v2 builder differences:
- No CPUGroupID: legacy nil vs v2 empty CpuGroup struct
- No StorageQoS: legacy nil vs v2 empty StorageQoS struct
- Initrd boot: legacy VPMem controller vs v2 nil VirtualPMem

Gap tests use inverted assertions — they expect a diff and only fail if
documents unexpectedly match, signaling the v2 bug was fixed.

Also adds normalizeKernelCmdLine and isOnlyKernelCmdLineWhitespaceDiff
helpers to handle a known legacy quirk where initrd+KernelDirect boot
produces a leading space in kernel command lines that v2 correctly omits.

Signed-off-by: Shreyansh Sancheti <shsancheti@microsoft.com>

Author: Shreyansh Sancheti

test/parity/vm/hcs_document_creator_test.go

@@ -8,10 +8,13 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"github.com/opencontainers/runtime-spec/specs-go"
 
+	"github.com/google/go-cmp/cmp"
+
 	runhcsopts "github.com/Microsoft/hcsshim/cmd/containerd-shim-runhcs-v1/options"
 	lcowbuilder "github.com/Microsoft/hcsshim/internal/builder/vm/lcow"
 	hcsschema "github.com/Microsoft/hcsshim/internal/hcs/schema2"
@@ -111,3 +114,74 @@ func jsonToString(v interface{}) string {
 	}
 	return string(b)
 }
+
+// normalizeKernelCmdLine trims leading/trailing whitespace from the kernel
+// command line in the document. The legacy builder has a minor quirk that
+// produces a leading space for initrd+KernelDirect boot. The v2 builder
+// does not. Since HCS trims whitespace from kernel args, this difference
+// is harmless and we normalize it away.
+func normalizeKernelCmdLine(doc *hcsschema.ComputeSystem) {
+	if doc == nil || doc.VirtualMachine == nil || doc.VirtualMachine.Chipset == nil {
+		return
+	}
+	if kd := doc.VirtualMachine.Chipset.LinuxKernelDirect; kd != nil {
+		kd.KernelCmdLine = strings.TrimSpace(kd.KernelCmdLine)
+	}
+	if uefi := doc.VirtualMachine.Chipset.Uefi; uefi != nil && uefi.BootThis != nil {
+		uefi.BootThis.OptionalData = strings.TrimSpace(uefi.BootThis.OptionalData)
+	}
+}
+
+// isOnlyKernelCmdLineWhitespaceDiff returns true if the only difference between
+// two documents is leading/trailing whitespace in the kernel command line.
+// This is a known legacy quirk where initrd+KernelDirect boot produces a
+// leading space that v2 correctly omits.
+func isOnlyKernelCmdLineWhitespaceDiff(legacy, v2 *hcsschema.ComputeSystem) bool {
+	// Deep copy and normalize, then re-compare.
+	legacyCopy := *legacy
+	v2Copy := *v2
+	// Shallow copy the VM and chipset to avoid mutating originals.
+	if legacyCopy.VirtualMachine != nil {
+		vmCopy := *legacyCopy.VirtualMachine
+		legacyCopy.VirtualMachine = &vmCopy
+		if vmCopy.Chipset != nil {
+			chipCopy := *vmCopy.Chipset
+			legacyCopy.VirtualMachine.Chipset = &chipCopy
+			if chipCopy.LinuxKernelDirect != nil {
+				lkdCopy := *chipCopy.LinuxKernelDirect
+				legacyCopy.VirtualMachine.Chipset.LinuxKernelDirect = &lkdCopy
+			}
+			if chipCopy.Uefi != nil {
+				uefiCopy := *chipCopy.Uefi
+				legacyCopy.VirtualMachine.Chipset.Uefi = &uefiCopy
+				if uefiCopy.BootThis != nil {
+					btCopy := *uefiCopy.BootThis
+					legacyCopy.VirtualMachine.Chipset.Uefi.BootThis = &btCopy
+				}
+			}
+		}
+	}
+	if v2Copy.VirtualMachine != nil {
+		vmCopy := *v2Copy.VirtualMachine
+		v2Copy.VirtualMachine = &vmCopy
+		if vmCopy.Chipset != nil {
+			chipCopy := *vmCopy.Chipset
+			v2Copy.VirtualMachine.Chipset = &chipCopy
+			if chipCopy.LinuxKernelDirect != nil {
+				lkdCopy := *chipCopy.LinuxKernelDirect
+				v2Copy.VirtualMachine.Chipset.LinuxKernelDirect = &lkdCopy
+			}
+			if chipCopy.Uefi != nil {
+				uefiCopy := *chipCopy.Uefi
+				v2Copy.VirtualMachine.Chipset.Uefi = &uefiCopy
+				if uefiCopy.BootThis != nil {
+					btCopy := *uefiCopy.BootThis
+					v2Copy.VirtualMachine.Chipset.Uefi.BootThis = &btCopy
+				}
+			}
+		}
+	}
+	normalizeKernelCmdLine(&legacyCopy)
+	normalizeKernelCmdLine(&v2Copy)
+	return cmp.Diff(&legacyCopy, &v2Copy) == ""
+}