diff --git a/docs/cultnet-transport-parity.md b/docs/cultnet-transport-parity.md
index d0779196..cda2dfb3 100644
--- a/docs/cultnet-transport-parity.md
+++ b/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
diff --git a/packages/cultmesh-kotlin/build.ps1 b/packages/cultmesh-kotlin/build.ps1
index aabacbcd..e744cb02 100644
--- a/packages/cultmesh-kotlin/build.ps1
+++ b/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"
diff --git a/packages/cultnet-ts/test/interop/cultnet-interop.test.ts b/packages/cultnet-ts/test/interop/cultnet-interop.test.ts
index 756ef97d..d2e7b71e 100644
--- a/packages/cultnet-ts/test/interop/cultnet-interop.test.ts
+++ b/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,