Update GaCy-GO

tools/go-toolchain.ps1

@@ -4,6 +4,10 @@ function Get-GoVersion([string]$Executable) {
     if ($LASTEXITCODE -ne 0 -or "$output" -notmatch '\bgo(\d+\.\d+(?:\.\d+)?)\b') { return $null }
     return [version]$Matches[1]
 }
+function Confirm-GoToolchainInstall([version]$Minimum) {
+    $answer = Read-Host "Go >= $Minimum is required to build. Download and install it now? [y/N]"
+    return $answer -match '^(?i:y|yes)$'
+}
 function Resolve-GoToolchain($Config) {
     $directive = Select-String -LiteralPath (Resolve-ProjectPath 'go.mod') -Pattern '^go\s+(\d+\.\d+(?:\.\d+)?)\s*$' | Select-Object -First 1
     if (-not $directive) { throw 'go.mod has no valid minimum Go version.' }
@@ -30,6 +34,7 @@ function Resolve-GoToolchain($Config) {
             if ($version -and $version -ge $minimum) { return $cached }
         }
     }
+    if (-not (Confirm-GoToolchainInstall $minimum)) { throw 'Go installation was declined. Install a compatible Go version, then run the build again.' }
     $machineArch = $env:PROCESSOR_ARCHITEW6432
     if (-not $machineArch) { $machineArch = $env:PROCESSOR_ARCHITECTURE }
     $arch = switch ($machineArch.ToUpperInvariant()) { 'AMD64' {'amd64'} 'ARM64' {'arm64'} 'X86' {'386'} default {throw "Unsupported Windows architecture: $machineArch"} }