test(M00): add checkpoint perceptual comparison

Work-Package: M00-QAR-VISUAL-DIFF-001
Agent: sindo-main-codex
Tests: synthetic visual diff, M00 dry-run, coordination and documentation gates
Fidelity: automates paired metrics; approved 3.3.5a captures and human approval remain required

tools/run_render_baseline.ps1

@@ -5,6 +5,8 @@ param(
     [string]$CacheState = "existing",
     [double]$WaitSeconds = 8.0,
     [double]$MeasureSeconds = 3.0,
+    [string]$ReferenceCheckpointDirectory,
+    [string]$VisualComparisonReport = "user://render_baseline/visual_comparison.json",
     [switch]$DryRun
 )
 
@@ -57,6 +59,19 @@ try {
         $captureArgs = @("--headless") + $captureArgs + @("--dry-run")
     }
     Invoke-GodotStep "capture" $captureArgs
+    if ($ReferenceCheckpointDirectory) {
+        if ($DryRun) {
+            throw "Reference checkpoint comparison requires PNG capture; remove -DryRun"
+        }
+        Invoke-GodotStep "visual-comparison" @(
+            "--headless", "--path", ".",
+            "--script", "res://src/tools/compare_render_checkpoints.gd",
+            "--",
+            "--reference", $ReferenceCheckpointDirectory,
+            "--candidate", $Output,
+            "--output", $VisualComparisonReport
+        )
+    }
     Write-Host "Renderer baseline completed. Report: $Output/report.json"
 } finally {
     Pop-Location