Add cross-runtime interop workflow

.github/workflows/cultnet-interop.yml

@@ -0,0 +1,79 @@
+name: CultNet cross-runtime interop
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  interop:
+    name: C# / TypeScript / Rust / Python / Kotlin
+    runs-on: windows-latest
+    timeout-minutes: 30
+
+    env:
+      DOTNET: dotnet
+      CARGO: cargo
+      PYTHON: python
+      KOTLIN_VERSION: 2.2.21
+
+    steps:
+      - name: Check out CultLib
+        uses: actions/checkout@v4
+
+      - name: Set up .NET
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: 10.0.x
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 24
+          cache: npm
+          cache-dependency-path: |
+            packages/cultcache-ts/package-lock.json
+            packages/cultnet-ts/package-lock.json
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Set up Rust
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Set up Java
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: "21"
+
+      - name: Install Kotlin compiler
+        shell: pwsh
+        run: |
+          $ErrorActionPreference = "Stop"
+          $version = $env:KOTLIN_VERSION
+          $zip = Join-Path $env:RUNNER_TEMP "kotlin-compiler-$version.zip"
+          $root = Join-Path $env:RUNNER_TEMP "kotlin"
+          Invoke-WebRequest "https://github.com/JetBrains/kotlin/releases/download/v$version/kotlin-compiler-$version.zip" -OutFile $zip
+          Expand-Archive -Path $zip -DestinationPath $root -Force
+          $kotlinHome = Join-Path $root "kotlinc"
+          if (-not (Test-Path (Join-Path $kotlinHome "bin\kotlinc.bat"))) {
+            throw "Kotlin compiler was not expanded to $kotlinHome"
+          }
+          "KOTLIN_HOME=$kotlinHome" | Out-File -FilePath $env:GITHUB_ENV -Append
+          "KOTLIN_JAVA_HOME=$env:JAVA_HOME" | Out-File -FilePath $env:GITHUB_ENV -Append
+          "$kotlinHome\bin" | Out-File -FilePath $env:GITHUB_PATH -Append
+
+      - name: Install Node dependencies
+        run: npm install --no-package-lock
+
+      - name: Build Kotlin interop peer
+        shell: pwsh
+        run: .\packages\cultmesh-kotlin\build.ps1
+
+      - name: Run cross-runtime interop harness
+        run: npm run test:interop --workspace packages/cultnet-ts