Ack Cut K0: portable cultmesh-kotlin build.ps1, pwsh interop harness, Kotlin parity note

build.ps1 picks kotlinc/kotlinc.bat and java/java.exe by platform and joins
paths and the classpath with the platform separator, so it runs under
PowerShell 7 on Linux (Yggdrasil's Kotlin verify image) and unchanged on
Windows. The TypeScript interop harness invokes pwsh off Windows. The parity
doc says twice that Kotlin does not yet conform to its RUDP claims until the
ack campaign's Cut K lands.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docs/cultnet-transport-parity.md

@@ -39,6 +39,8 @@ language now converge across the targeted runtimes, while production service
 adoption still varies by runtime and older TCP/LiteNetLib/WebSocket bodies have
 not all been lowered behind the shared transport port.
 
+> **Kotlin does not yet conform to the RUDP claims in this document.** `CultMesh.kt` lacks the stray-packet hardening of `3bf1c0c`, and it will lack the ack, receipt, FORWARD-TSN and expiry work of the ack campaign until that campaign's Cut K lands. Read every RUDP statement here as covering C#, TypeScript, Rust and Python only.
+
 ## Invariants
 
 - `cultnet.schema.v0` payloads are transport-neutral. Message schemas must not
@@ -471,6 +473,8 @@ Current progress:
   core schema-message RUDP matrix is live in the TypeScript interop gate;
   broader service adoption remains the unclaimed layer.
 
+> **Kotlin does not yet conform to the RUDP claims in this document.** `CultMesh.kt` lacks the stray-packet hardening of `3bf1c0c`, and it will lack the ack, receipt, FORWARD-TSN and expiry work of the ack campaign until that campaign's Cut K lands. Read every RUDP statement here as covering C#, TypeScript, Rust and Python only.
+
 ## RUDP Packet Contract V0
 
 `cultnet.transport.rudp.v0` packets start with a fixed binary header, followed

packages/cultmesh-kotlin/build.ps1

@@ -4,26 +4,28 @@ param(
 )
 
 $ErrorActionPreference = "Stop"
+$onWindows = [Environment]::OSVersion.Platform -eq [PlatformID]::Win32NT
+$pathSeparator = [IO.Path]::PathSeparator
 $repoRoot = Split-Path -Parent (Split-Path -Parent $PSScriptRoot)
-$src = Join-Path $PSScriptRoot "src\main\kotlin"
-$out = Join-Path $repoRoot "artifacts\cultmesh-kotlin"
+$src = Join-Path $PSScriptRoot (Join-Path "src" (Join-Path "main" "kotlin"))
+$out = Join-Path (Join-Path $repoRoot "artifacts") "cultmesh-kotlin"
 $jarPath = Join-Path $out "cultmesh-kotlin.jar"
-$kotlinc = Join-Path $KotlinHome "bin\kotlinc.bat"
-$kotlinStdlib = Join-Path $KotlinHome "lib\kotlin-stdlib.jar"
-$java = Join-Path $JavaHome "bin\java.exe"
+$kotlinc = Join-Path (Join-Path $KotlinHome "bin") $(if ($onWindows) { "kotlinc.bat" } else { "kotlinc" })
+$kotlinStdlib = Join-Path (Join-Path $KotlinHome "lib") "kotlin-stdlib.jar"
+$java = Join-Path (Join-Path $JavaHome "bin") $(if ($onWindows) { "java.exe" } else { "java" })
 
 if (-not (Test-Path $kotlinc)) { throw "kotlinc not found: $kotlinc" }
 if (-not (Test-Path $kotlinStdlib)) { throw "kotlin stdlib not found: $kotlinStdlib" }
 if (-not (Test-Path $java)) { throw "java not found: $java" }
 
 $env:JAVA_HOME = $JavaHome
-$env:PATH = "$(Join-Path $JavaHome 'bin');$env:PATH"
+$env:PATH = "$(Join-Path $JavaHome 'bin')$pathSeparator$env:PATH"
 
 Remove-Item -Recurse -Force -ErrorAction SilentlyContinue $out
 New-Item -ItemType Directory -Force $out | Out-Null
 $sources = Get-ChildItem $src -Recurse -Filter *.kt | Select-Object -ExpandProperty FullName
 & $kotlinc @sources -jvm-target 1.8 -classpath $kotlinStdlib -d $jarPath
 if ($LASTEXITCODE -ne 0) { throw "kotlinc failed with exit code $LASTEXITCODE" }
-& $java -cp "$jarPath;$kotlinStdlib" org.gamecult.cultmesh.CultMeshKt
+& $java -cp "$jarPath$pathSeparator$kotlinStdlib" org.gamecult.cultmesh.CultMeshKt
 if ($LASTEXITCODE -ne 0) { throw "cultmesh-kotlin self-test failed with exit code $LASTEXITCODE" }
 Write-Host "Built $jarPath"

packages/cultnet-ts/test/interop/cultnet-interop.test.ts

@@ -2798,7 +2798,7 @@ async function runDotnetTestFilter(
 
 async function buildKotlinInteropPeer(): Promise<void> {
   kotlinInteropPeerBuild ??= execFileAsync(
-    "powershell",
+    process.platform === "win32" ? "powershell" : "pwsh",
     ["-NoProfile", "-ExecutionPolicy", "Bypass", "-File", resolve(cultmeshKotlinRoot, "build.ps1")],
     {
       cwd: cultLibRoot,