Require PowerShell 7.5+ in Build.ps1 and DockerBuild.ps1

Scripts now fail with a clear error message if run with an older
PowerShell version, instructing users to use 'pwsh' instead of 'powershell'.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: gfraiteur

src/PostSharp.Engineering.BuildTools/Resources/Build.ps1

@@ -12,6 +12,13 @@ param(
     [string[]]$BuildArgs   # Arguments passed to `Build.ps1` within the container.
 )
 
+# Require PowerShell 7.5 or higher (run with pwsh, not powershell)
+if ($PSVersionTable.PSVersion -lt [Version]'7.5')
+{
+    Write-Error "This script requires PowerShell 7.5 or higher (run with 'pwsh', not 'powershell'). Current version: $($PSVersionTable.PSVersion)"
+    exit 1
+}
+
 ####
 # These settings are replaced by the generate-scripts command.
 $EngPath = '<ENG_PATH>'

src/PostSharp.Engineering.BuildTools/Resources/DockerBuild.ps1

@@ -29,6 +29,13 @@ param(
     [string[]]$BuildArgs   # Arguments passed to `Build.ps1` within the container (or Claude prompt if -Claude is specified).
 )
 
+# Require PowerShell 7.5 or higher (run with pwsh, not powershell)
+if ($PSVersionTable.PSVersion -lt [Version]'7.5')
+{
+    Write-Error "This script requires PowerShell 7.5 or higher (run with 'pwsh', not 'powershell'). Current version: $($PSVersionTable.PSVersion)"
+    exit 1
+}
+
 ####
 # These settings are replaced by the generate-scripts command.
 $EngPath = '<ENG_PATH>'