Stage session-marker executable directly from task-specific linker output

Build-SessionMarker.ps1

@@ -0,0 +1,39 @@
+param([switch]$StageOnly, [string]$DependencyTargetDirectory = (Join-Path $PSScriptRoot 'target'))
+$ErrorActionPreference = 'Stop'
+$privateDirectory = Join-Path $PSScriptRoot '.local/session-marker'
+$buildDirectory = Join-Path $privateDirectory 'build'
+$artifact = Join-Path $buildDirectory 'skate3rust-session-marker.exe'
+$destination = Join-Path $privateDirectory 'skate3-session-marker.exe'
+Push-Location $PSScriptRoot
+$previousFlags = $env:CARGO_TARGET_X86_64_PC_WINDOWS_MSVC_RUSTFLAGS
+try {
+    New-Item -ItemType Directory -Force -Path $buildDirectory | Out-Null
+    if (-not $StageOnly) {
+        $env:CARGO_TARGET_X86_64_PC_WINDOWS_MSVC_RUSTFLAGS = '-C target-feature=+crt-static'
+        # Dependencies may use a shared cache. The linker writes this task's
+        # artifact directly, never staging the cache's generic skate3rust.exe.
+        & cargo rustc --release --locked --target x86_64-pc-windows-msvc `
+            --target-dir $DependencyTargetDirectory -p skate-game --no-default-features `
+            --bin skate3rust -- -C extra-filename=-session-marker `
+            -o (Join-Path $buildDirectory 'skate3rust.exe')
+        if ($LASTEXITCODE -ne 0) { throw 'Session-marker build failed.' }
+    }
+    $bytes = [System.IO.File]::ReadAllBytes($artifact)
+    $text = [System.Text.Encoding]::ASCII.GetString($bytes)
+    foreach ($required in @('--start-paused', 'session_marker/effect.wgsl', 'Session marker return rejected')) {
+        if (-not $text.Contains($required)) { throw "Wrong session-marker artifact: missing $required" }
+    }
+    Copy-Item -LiteralPath $artifact -Destination $destination -Force
+    $hash = (Get-FileHash -LiteralPath $destination -Algorithm SHA256).Hash
+    if ($hash -ne (Get-FileHash -LiteralPath $artifact -Algorithm SHA256).Hash) {
+        throw 'Staged executable hash mismatch.'
+    }
+    @{ executable = $destination; sha256 = $hash; source = $PSScriptRoot;
+       revision = (& git rev-parse HEAD); staticChecks = 'CLI, marker shader, return path' } |
+        ConvertTo-Json | Set-Content -LiteralPath (Join-Path $privateDirectory 'build-manifest.json') -Encoding UTF8
+    Write-Host "Ready for manual launch: $destination"
+    Write-Host "SHA256: $hash"
+} finally {
+    $env:CARGO_TARGET_X86_64_PC_WINDOWS_MSVC_RUSTFLAGS = $previousFlags
+    Pop-Location
+}