feat: include mutagen binary in installer (#47)

`Publish.ps1` now downloads (if unmodified) the necessary mutagen files
from our GCS bucket. These files aren't checked into the repo since they
are large, but they will be cached and ignored in the workdir.

`mutagen.exe` and `mutagen-agents.tar.gz` will appear in the same
directory as `wintun.dll` in the install.

```powershell
PS C:\Users\dean\git\coder-desktop-windows> ls .\publish\buildtemp-1.2.3.4-x64\vpn


    Directory: C:\Users\dean\git\coder-desktop-windows\publish\buildtemp-1.2.3.4-x64\vpn


Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
-a----         1/03/2025     12:02           5431 LICENSE.WINTUN.txt
-a----        10/03/2025     11:58       17964207 mutagen-agents.tar.gz
-a----        10/03/2025     11:58       13797376 mutagen.exe
-a----         1/03/2025     15:20         427552 wintun.dll
```

Updating to a new mutagen version is as simple as updating
`$mutagenVersion` in `Publish.ps1`.

Closes #25

Author: deansheather

scripts/Publish.ps1

@@ -83,6 +83,30 @@ function Add-CoderSignature([string] $path) {
     }
 }
 
+function Download-File([string] $url, [string] $outputPath, [string] $etagFile) {
+    Write-Host "Downloading '$url' to '$outputPath'"
+    # We use `curl.exe` here because `Invoke-WebRequest` is notoriously slow.
+    & curl.exe `
+        --progress-bar `
+        --show-error `
+        --fail `
+        --location `
+        --etag-compare $etagFile `
+        --etag-save $etagFile `
+        --output $outputPath `
+        $url
+    if ($LASTEXITCODE -ne 0) { throw "Failed to download $url" }
+    if (!(Test-Path $outputPath) -or (Get-Item $outputPath).Length -eq 0) {
+        throw "Failed to download '$url', output file '$outputPath' is missing or empty"
+    }
+}
+
+$goArch = switch ($arch) {
+    "x64" { "amd64" }
+    "arm64" { "arm64" }
+    default { throw "Unsupported architecture: $arch" }
+}
+
 # CD to the root of the repo
 $repoRoot = Resolve-Path (Join-Path $PSScriptRoot "..")
 Push-Location $repoRoot
@@ -145,6 +169,24 @@ if ($null -eq $wintunDllSrc) {
 $wintunDllDest = Join-Path $vpnFilesPath "wintun.dll"
 Copy-Item $wintunDllSrc $wintunDllDest
 
+# Download the mutagen binary from our bucket for this platform if we don't have
+# it yet (or it's different).
+$mutagenVersion = "v0.18.1"
+$mutagenSrcPath = Join-Path $repoRoot "scripts\files\mutagen-windows-$($goArch).exe"
+$mutagenSrcUrl = "https://storage.googleapis.com/coder-desktop/mutagen/$($mutagenVersion)/mutagen-windows-$($goArch).exe"
+$mutagenEtagFile = $mutagenSrcPath + ".etag"
+Download-File $mutagenSrcUrl $mutagenSrcPath $mutagenEtagFile
+$mutagenDestPath = Join-Path $vpnFilesPath "mutagen.exe"
+Copy-Item $mutagenSrcPath $mutagenDestPath
+
+# Download mutagen agents tarball.
+$mutagenAgentsSrcPath = Join-Path $repoRoot "scripts\files\mutagen-agents.tar.gz"
+$mutagenAgentsSrcUrl = "https://storage.googleapis.com/coder-desktop/mutagen/$($mutagenVersion)/mutagen-agents.tar.gz"
+$mutagenAgentsEtagFile = $mutagenAgentsSrcPath + ".etag"
+Download-File $mutagenAgentsSrcUrl $mutagenAgentsSrcPath $mutagenAgentsEtagFile
+$mutagenAgentsDestPath = Join-Path $vpnFilesPath "mutagen-agents.tar.gz"
+Copy-Item $mutagenAgentsSrcPath $mutagenAgentsDestPath
+
 # Build the MSI installer
 & dotnet.exe run --project .\Installer\Installer.csproj -c Release -- `
     build-msi `

scripts/files/.gitignore

@@ -0,0 +1,3 @@
+mutagen-*.tar.gz
+mutagen-*.exe
+*.etag