build: default version from Directory.Build.props; allow -Version override

Remove git tag fallback and read AppVersion/PrereleaseLabel from props. Only pass -p:Version when override is provided; otherwise defer to MSBuild evaluation.

src/build.ps1

@@ -5,7 +5,7 @@
     pwsh ./build.ps1                      # build all
     pwsh ./build.ps1 -Targets win         # just Windows
     pwsh ./build.ps1 -Targets web,android # pick targets
-    pwsh ./build.ps1 -Version 1.2.3       # override version (else tries git tag)
+    pwsh ./build.ps1 -Version 1.2.3       # override version (default comes from Directory.Build.props)
 #>
 
 param(
@@ -60,17 +60,40 @@ function Invoke-InProjectDir {
   }
 }
 
-# --- Version (git tag 'vX.Y.Z' > explicit > empty) ---
-if (-not $Version) {
+# --- Version (default from Directory.Build.props unless overridden) ---
+function Get-VersionFromProps {
+  param([Parameter(Mandatory=$true)][string]$PropsPath)
+  if (-not (Test-Path $PropsPath)) { return $null }
   try {
-    $tag = (git describe --tags --abbrev=0) 2>$null
-    if ($LASTEXITCODE -eq 0 -and $tag) { $Version = $tag.TrimStart('v') }
-  } catch { }
+    $xml = [xml](Get-Content -Raw -Path $PropsPath)
+    $groups = @($xml.Project.PropertyGroup)
+    $app = ($groups | ForEach-Object { $_.AppVersion } | Where-Object { $_ -and $_.Trim() -ne '' } | Select-Object -First 1)
+    $pre = ($groups | ForEach-Object { $_.PrereleaseLabel } | Where-Object { $_ -and $_.Trim() -ne '' } | Select-Object -First 1)
+    if ($app) {
+      if ($pre) { return "$app-$pre" }
+      return $app
     }
-if ($Version) {
+  } catch { }
+  return $null
+}
+
+$ExplicitVersion = $false
+if ($PSBoundParameters.ContainsKey('Version') -and $Version) { $ExplicitVersion = $true }
+
+$DerivedVersion = $null
+if (-not $ExplicitVersion) {
+  $DerivedVersion = Get-VersionFromProps (Join-Path $Root 'Directory.Build.props')
+}
+
+if ($ExplicitVersion) {
   # Normalize to SemVer with 3 numeric segments (X.Y.Z)
   if ($Version -match '^(\d+)\.(\d+)$') { $Version = "$Version.0" }
-  Write-Host "Using Version: $Version" -ForegroundColor Yellow
+  Write-Host "Using Version (override): $Version" -ForegroundColor Yellow
+} elseif ($DerivedVersion) {
+  if ($DerivedVersion -match '^(\d+)\.(\d+)$') { $DerivedVersion = "$DerivedVersion.0" }
+  Write-Host "Using Version (from Directory.Build.props): $DerivedVersion" -ForegroundColor Yellow
+} else {
+  Write-Host "No explicit version provided; MSBuild will compute Version from Directory.Build.props." -ForegroundColor Yellow
 }
 
 # --- Ensure SDK/workloads present ---
@@ -90,7 +113,7 @@ if ($Targets -contains 'win') {
     '-p:IncludeNativeLibrariesForSelfExtract=true',
     '-o', $OutWin
   )
-  if ($Version) { $args += "-p:Version=$Version" }
+  if ($ExplicitVersion) { $args += "-p:Version=$Version" }
   # Prevent '+<sha>' being appended to informational version in artifacts
   $args += '-p:IncludeSourceRevisionInInformationalVersion=false'
   Invoke-InProjectDir -ProjectPath $ProjDesktop @args
@@ -105,7 +128,7 @@ if ($Targets -contains 'web') {
     '--self-contained', 'true',
     '-o', $OutWeb
   )
-  if ($Version) { $args += "-p:Version=$Version" }
+  if ($ExplicitVersion) { $args += "-p:Version=$Version" }
   $args += '-p:IncludeSourceRevisionInInformationalVersion=false'
   Invoke-InProjectDir -ProjectPath $ProjWeb @args
 
@@ -125,7 +148,7 @@ if ($Targets -contains 'android') {
     '-p:AndroidPackageFormat=apk',
     '-o', $OutDroid
   )
-  if ($Version) { $baseArgs += "-p:Version=$Version" }
+  if ($ExplicitVersion) { $baseArgs += "-p:Version=$Version" }
   $baseArgs += '-p:IncludeSourceRevisionInInformationalVersion=false'
 
   # Unsigned build