ci(render): Campaign V slice V9 - the Vulkan gate runs on lavapipe

The first CI job in this project's history that renders a frame.

The whole row rests on a decision V6g already made and paid for. When
section 5.5.8 cut set 0 from ten dynamic storage descriptors to four, four
was not merely under the RX 9070 XT's eight - it is Vulkan's guaranteed
minimum, so no conformant device can fail the layout. That is what makes a
software-device row possible at all. Every other requirement was then
checked against Mesa's lvp_device.c rather than assumed, and all seventeen
features the gate demands are true on lavapipe - including
samplerAnisotropy, which V7 made load-bearing eight commits ago and which a
software rasterizer would have been entirely within its rights to decline.

Three things had to exist before the job could:

1. The harness could not stop. VulkanBringUpHost presents until its window
   closes, which is right at a desk and impossible in CI, where nothing ever
   closes a window. ACDREAM_VULKAN_PROBE_FRAMES gives it a budget; unset or
   malformed is zero, which keeps the interactive behaviour, so no existing
   invocation changes. The budget never cuts the capture short - the loop
   stays open until the screenshot has been attempted - because a run whose
   entire product is a PNG must not be able to exit green with an empty
   artifact directory. The decision is a pure static method, tested without
   a window or a driver.

2. tools/compile-shaders.ps1 was Windows-only and nobody had noticed,
   because nothing had ever run it anywhere else. It built its paths from
   embedded 'src\AcDream.App\...' literals; a backslash is a separator on
   Windows and an ordinary filename character everywhere else, so on Linux
   that is one long nonexistent file name.

3. The report's jq paths were invisible to the compiler. Renaming a record
   property or swapping the enum converter would have left every test green
   and turned CI red on someone else's branch days later, with a failure
   that reads like a driver problem. VulkanCapabilityReportContractTests
   pins the exact strings the job greps and pins its packed-version
   arithmetic against VulkanApiVersion's own unpacking.

The job, eleven steps: install lavapipe and Xvfb; record vulkaninfo as
evidence; publish linux-x64; run the Gpu.Vk tests on a second operating
system; probe the gate under a 24-bit Xvfb screen (the default is 8-bit,
which leaves the X11 WSI without a usable visual) and assert an accepting
verdict on a Cpu device at API >= 1.3 with a clean active probe; assert the
captured PNG is a real frame by IHDR dimensions and byte count; re-run with
ACDREAM_VULKAN_FORCE_UNSUPPORTED=timelineSemaphore and assert exit 4 with an
actionable refusal; recompile the shaders and compare. Artifacts upload on
always(), so a red run ships its own diagnosis.

The .spv step is what ties the committed binaries to their sources. The
existing App test hashes GLSL against the manifest, which catches "edited a
shader, forgot to recompile"; nothing caught a stale or hand-edited .spv.
Verified on Windows before shipping: 19/19 artifacts byte-identical to a
fresh compile, zero drift.

No GL-versus-Vulkan pixel compare, for two independent reasons recorded in
section 5.5.20: linux-graphical asserts exit 4, so there is no left-hand
side, and the probe renders synthetic scenes rather than the DAT world CI
cannot have. The two jobs now say something sharper than a pixel diff would
have - on the same software Mesa stack, GL is refused and Vulkan is accepted
and draws. Physical Linux GPU and Wayland rows stay deferred on the Slice L
precedent; no hosted runner offers either.

Gates: Release build green, zero errors. App tests 4,152 / 3 skipped against
a 4,134 / 3 baseline at this branch's base (9b7f4343) - eighteen new, all
from this slice. Workflow validated by a real YAML parse plus an Actions
schema check and bash -n over all nine extracted run blocks; no actionlint
was available locally and none was downloaded. The job itself has not run:
its first execution is the CI run this commit triggers, and the V9 row stays
partial until that is green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tools/compile-shaders.ps1

@@ -48,8 +48,14 @@ param(
 
 $ErrorActionPreference = 'Stop'
 $repo = Split-Path -Parent $PSScriptRoot
+# Campaign V slice V9: every path below is composed one segment at a time rather
+# than from an embedded 'a\b\c' literal. A backslash is a path separator on
+# Windows and an ordinary filename character everywhere else, so the embedded
+# form silently produced one long nonexistent file name on the Linux CI runner
+# that this slice's lavapipe job introduced.
 if (-not $ShadersDirectory) {
-    $ShadersDirectory = Join-Path $repo 'src\AcDream.App\Rendering\Shaders'
+    $ShadersDirectory = [System.IO.Path]::Combine(
+        $repo, 'src', 'AcDream.App', 'Rendering', 'Shaders')
 }
 if (-not $OutputDirectory) {
     $OutputDirectory = Join-Path $ShadersDirectory 'spv'
@@ -67,8 +73,14 @@ if ($PreferSdk) {
         $glslc = $onPath.Source
     }
     elseif ($env:VULKAN_SDK) {
-        $candidate = Join-Path $env:VULKAN_SDK 'Bin\glslc.exe'
-        if (Test-Path $candidate) { $glslc = $candidate }
+        # 'Bin/glslc.exe' on Windows, 'bin/glslc' on the SDK's Linux layout.
+        $candidates = @(
+            [System.IO.Path]::Combine($env:VULKAN_SDK, 'Bin', 'glslc.exe'),
+            [System.IO.Path]::Combine($env:VULKAN_SDK, 'bin', 'glslc')
+        )
+        foreach ($candidate in $candidates) {
+            if (Test-Path $candidate) { $glslc = $candidate; break }
+        }
     }
 }
 
@@ -84,12 +96,15 @@ else {
     Write-Step 'no Vulkan SDK glslc found; using the managed Silk.NET.Shaderc compiler'
 }
 
-$tool = Join-Path $repo 'tools\ShaderCompiler\ShaderCompiler.csproj'
+$tool = [System.IO.Path]::Combine(
+    $repo, 'tools', 'ShaderCompiler', 'ShaderCompiler.csproj')
 Write-Step 'building the shader compiler'
 & dotnet build $tool -c Release --nologo -v q | Out-Null
 if ($LASTEXITCODE -ne 0) { throw "Shader compiler build failed with exit code $LASTEXITCODE." }
 
-$binary = Join-Path $repo 'tools\ShaderCompiler\bin\Release\net10.0\AcDream.Tools.ShaderCompiler.dll'
+$binary = [System.IO.Path]::Combine(
+    $repo, 'tools', 'ShaderCompiler', 'bin', 'Release', 'net10.0',
+    'AcDream.Tools.ShaderCompiler.dll')
 if (-not (Test-Path $binary)) { throw "Shader compiler not found at $binary." }
 
 Write-Step "compiling $ShadersDirectory -> $OutputDirectory"