fix: address PR #60 review feedback

- SizeParser: wrap TB-suffix overflow in try/catch so callers get
  ArgumentException with the parameter name rather than OverflowException.
- New-PveVm/New-PveContainer: validate -DiskSize/-RootFsSize before
  ShouldProcess so typos like "512M" are rejected even with -WhatIf and
  even when the matching -DiskStorage/-RootFsStorage is omitted.
- Add Pester tests for the new DiskSize and RootFsSize validation paths,
  including a new New-PveContainer.Tests.ps1.
- Add SizeParserTests coverage for the TB overflow path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/PSProxmoxVE.Core/Utilities/SizeParser.cs

@@ -59,7 +59,13 @@ namespace PSProxmoxVE.Core.Utilities
                 case "T":
                 case "TB":
                 case "TIB":
-                    gib = checked(num * 1024L);
+                    try { gib = checked(num * 1024L); }
+                    catch (OverflowException)
+                    {
+                        throw new ArgumentException(
+                            $"{parameterName} '{value}' is too large to represent in GiB.",
+                            parameterName);
+                    }
                     break;
                 default:
                     throw new ArgumentException(

src/PSProxmoxVE/Cmdlets/Containers/NewPveContainerCmdlet.cs

@@ -130,6 +130,13 @@ namespace PSProxmoxVE.Cmdlets.Containers
 
         protected override void ProcessRecord()
         {
+            // Validate -RootFsSize before ShouldProcess so typos like "512M" are rejected
+            // even with -WhatIf, and so the error is raised regardless of whether
+            // -RootFsStorage is also supplied.
+            string? rootFsSizeGib = null;
+            if (!string.IsNullOrEmpty(RootFsSize))
+                rootFsSizeGib = SizeParser.NormalizeToGibibytes(RootFsSize!, nameof(RootFsSize));
+
             if (!ShouldProcess($"Container on node '{Node}'", "New-PveContainer"))
                 return;
 
@@ -165,11 +172,8 @@ namespace PSProxmoxVE.Cmdlets.Containers
             if (!string.IsNullOrEmpty(RootFsStorage))
             {
                 var rootFsValue = RootFsStorage!;
-                if (!string.IsNullOrEmpty(RootFsSize))
-                {
-                    var sizeGib = SizeParser.NormalizeToGibibytes(RootFsSize!, nameof(RootFsSize));
-                    rootFsValue += $":{sizeGib}";
-                }
+                if (rootFsSizeGib != null)
+                    rootFsValue += $":{rootFsSizeGib}";
                 config["rootfs"] = rootFsValue;
             }
 

src/PSProxmoxVE/Cmdlets/Vms/NewPveVmCmdlet.cs

@@ -128,6 +128,13 @@ namespace PSProxmoxVE.Cmdlets.Vms
 
         protected override void ProcessRecord()
         {
+            // Validate -DiskSize before ShouldProcess so typos like "512M" are rejected
+            // even with -WhatIf, and so the error is raised regardless of whether
+            // -DiskStorage is also supplied.
+            string? diskSizeGib = null;
+            if (!string.IsNullOrEmpty(DiskSize))
+                diskSizeGib = SizeParser.NormalizeToGibibytes(DiskSize!, nameof(DiskSize));
+
             if (!ShouldProcess($"VM on node '{Node}'", "New-PveVm"))
                 return;
 
@@ -166,10 +173,9 @@ namespace PSProxmoxVE.Cmdlets.Vms
             if (!string.IsNullOrEmpty(OsType))
                 config["ostype"] = OsType!;
 
-            if (!string.IsNullOrEmpty(DiskStorage) && !string.IsNullOrEmpty(DiskSize))
+            if (!string.IsNullOrEmpty(DiskStorage) && diskSizeGib != null)
             {
-                var sizeGib = SizeParser.NormalizeToGibibytes(DiskSize!, nameof(DiskSize));
-                var diskValue = $"{DiskStorage}:{sizeGib}";
+                var diskValue = $"{DiskStorage}:{diskSizeGib}";
                 if (!string.IsNullOrEmpty(DiskFormat))
                     diskValue += $",format={DiskFormat}";
                 config["virtio0"] = diskValue;