Adds code signing to tagged windows builds (#4473)

**Note**: This change requires the addition of new entries in the
secrets to work properly. These should be added prior to this merging.

# Description of Changes

* Add a tag-only Windows signing job that runs on a self-hosted signing
runner.
* This is an alternative/separate code-path just for the signing job.
See **Alternatives Considered** for details.
* Skip the unsigned Windows matrix build on tags so signed artifacts are
the only Windows release outputs.
* Sign `spacetimedb-update.exe`, `spacetimedb-cli.exe`, and
`spacetimedb-standalone.exe` before packaging, then upload the signed
artifacts as usual.

# Alternatives Considered
**Inline signing in the existing Windows packaging step**. This was
rejected because it would require all Windows builds (including non-tag
builds) to run on the signing-capable runner or to install/signing
tooling on GitHub-hosted runners. The chosen approach isolates signing
to tag releases, avoids exposing credentials in standard builds, and
keeps routine CI behavior unchanged.

# API and ABI breaking changes

None

# Expected complexity level and risk

2 – low risk. CI-only change that adds a new signing job and preserves
existing artifact layout.

# Testing

- [X] None (Not running, workflow change only)

---------

Signed-off-by: Ryan <r.ekhoff@clockworklabs.io>
Co-authored-by: Zeke Foppa <196249+bfops@users.noreply.github.com>

Author: rekhoff

.github/workflows/package.yml

@@ -7,9 +7,12 @@ on:
     branches:
       - master
       - release/*
+permissions:
+  contents: read
 
 jobs:
   build-cli:
+    if: ${{ !(startsWith(github.ref, 'refs/tags/') && matrix.target == 'x86_64-pc-windows-msvc') }}
     strategy:
       fail-fast: false
       matrix:
@@ -85,3 +88,89 @@ jobs:
           source_dir: build
           endpoint: https://nyc3.digitaloceanspaces.com
           destination_dir: ${{ steps.extract_branch.outputs.branch }}
+
+  build-cli-windows-signed:
+    if: ${{ startsWith(github.ref, 'refs/tags/') }}
+    name: Build and sign CLI for x86_64 Windows
+    runs-on: [self-hosted, windows, signing]
+    environment: codesign
+    concurrency:
+      group: codesign-${{ github.ref }}
+      cancel-in-progress: false
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Install Rust
+        uses: dsherret/rust-toolchain-file@v1
+
+      - name: Install rust target
+        run: rustup target add x86_64-pc-windows-msvc
+
+      - name: Compile
+        run: |
+          cargo build --release --target x86_64-pc-windows-msvc -p spacetimedb-cli -p spacetimedb-standalone -p spacetimedb-update
+
+      - name: Write certificate file
+        shell: powershell
+        env:
+          DIGICERT_CERT_B64: ${{ secrets.DIGICERT_CERT_B64 }}
+        run: |
+          [IO.File]::WriteAllBytes("digicert.crt", [Convert]::FromBase64String($env:DIGICERT_CERT_B64))
+
+      - name: Sign binaries
+        shell: powershell
+        env:
+          DIGICERT_KEYPAIR_ALIAS: ${{ secrets.DIGICERT_KEYPAIR_ALIAS }}
+        run: |
+          $ErrorActionPreference = 'Stop'
+          $targetDir = Join-Path $env:GITHUB_WORKSPACE 'target\x86_64-pc-windows-msvc\release'
+          $certFile = Join-Path $env:GITHUB_WORKSPACE 'digicert.crt'
+
+          $signtool = Get-Command signtool.exe -ErrorAction Stop
+
+          $files = @(
+            (Join-Path $targetDir 'spacetimedb-update.exe'),
+            (Join-Path $targetDir 'spacetimedb-cli.exe'),
+            (Join-Path $targetDir 'spacetimedb-standalone.exe')
+          )
+
+          foreach ($file in $files) {
+            & $signtool.Path sign /csp "DigiCert Signing Manager KSP" /kc $env:DIGICERT_KEYPAIR_ALIAS /f $certFile /tr http://timestamp.digicert.com /td SHA256 /fd SHA256 $file
+            & $signtool.Path verify /v /pa $file
+          }
+
+      - name: Package (windows)
+        shell: powershell
+        run: |
+          $ErrorActionPreference = 'Stop'
+          New-Item -ItemType Directory -Force -Path build | Out-Null
+          $releaseDir = Join-Path $env:GITHUB_WORKSPACE 'target\x86_64-pc-windows-msvc\release'
+
+          Copy-Item (Join-Path $releaseDir 'spacetimedb-update.exe') (Join-Path $env:GITHUB_WORKSPACE 'build\spacetimedb-update-x86_64-pc-windows-msvc.exe')
+          Compress-Archive -Force -Path @(
+            (Join-Path $releaseDir 'spacetimedb-cli.exe'),
+            (Join-Path $releaseDir 'spacetimedb-standalone.exe')
+          ) -DestinationPath (Join-Path $env:GITHUB_WORKSPACE 'build\spacetime-x86_64-pc-windows-msvc.zip')
+
+      - name: Extract branch name
+        shell: powershell
+        run: |
+          $ErrorActionPreference = 'Stop'
+          $branch = $env:GITHUB_HEAD_REF
+          if ([string]::IsNullOrEmpty($branch)) {
+            $branch = $env:GITHUB_REF -replace '^refs/heads/', ''
+          }
+          "branch=$branch" | Out-File -FilePath $env:GITHUB_OUTPUT -Encoding utf8 -Append
+        id: extract_branch
+
+      - name: Upload to DO Spaces
+        uses: shallwefootball/s3-upload-action@master
+        with:
+          aws_key_id: ${{ secrets.AWS_KEY_ID }}
+          aws_secret_access_key: ${{ secrets.AWS_SECRET_ACCESS_KEY}}
+          aws_bucket: ${{ vars.AWS_BUCKET }}
+          source_dir: build
+          endpoint: https://nyc3.digitaloceanspaces.com
+          destination_dir: ${{ steps.extract_branch.outputs.branch }}