codegen: snapshot-driven generator + module split + correctness pass

Scripts/build_and_test.ps1

@@ -66,6 +66,23 @@ $cmd = Join-Path $Engine 'Engine\Binaries\Win64\UnrealEditor-Cmd.exe'
 if (-not (Test-Path $bat)) { Write-Error "Build.bat not found: $bat";          exit 3 }
 if (-not (Test-Path $cmd)) { Write-Error "UnrealEditor-Cmd not found: $cmd";   exit 3 }
 
+# --- Codegen drift gate ----------------------------------------------------
+# Refuse to build if codegen output drifted from the committed Source/, or
+# if any drift diagnostic (--strict) fires, or if the clang-AST introspect
+# snapshot is missing (--require-introspect). Skipped silently when Python
+# isn't on PATH — the gate is best-effort locally; CI enforces it strictly.
+$pluginRoot = Split-Path -Parent $PSScriptRoot
+$generator = Join-Path $pluginRoot 'Scripts/codegen/generate_ue_components.py'
+$py = (Get-Command python -ErrorAction SilentlyContinue)
+if ($py -and (Test-Path $generator)) {
+    Write-Host '>>> Codegen drift gate: python generate_ue_components.py --check --strict --require-introspect'
+    & $py.Source $generator --check --strict --require-introspect
+    if ($LASTEXITCODE -ne 0) {
+        Write-Error "Codegen drift detected (exit $LASTEXITCODE). Re-run 'python Scripts/codegen/generate_ue_components.py' to regenerate, then re-run this script."
+        exit 4
+    }
+}
+
 # Truncate the test log up-front so a build failure (or any early exit
 # before UnrealEditor-Cmd writes to it) doesn't leave the SHA-256 in the
 # summary pointing at a previous run's file.