Fix facility discovery in exported builds and verify first construction

tools/verify_exported_opening.py

@@ -0,0 +1,39 @@
+#!/usr/bin/env python3
+"""Exercise the distributed PCK with no source-tree fallback or player saves."""
+import argparse
+import os
+from pathlib import Path
+import shutil
+import subprocess
+import tempfile
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("pack", type=Path)
+    parser.add_argument("--godot", default="godot")
+    parser.add_argument("--capture", type=Path)
+    args = parser.parse_args()
+    pack = args.pack.resolve(strict=True)
+    godot = shutil.which(args.godot)
+    if godot is None:
+        parser.error(f"Godot executable not found: {args.godot}")
+    script = Path(__file__).resolve().parents[1] / "tests/export/test_exported_opening.gd"
+    env = dict(os.environ, THE_TREE_REQUIRE_EXPORTED="1")
+    command = [godot]
+    if args.capture:
+        output = args.capture.resolve()
+        output.parent.mkdir(parents=True, exist_ok=True)
+        env.update(THE_TREE_EXPORT_CAPTURE="1", THE_TREE_EXPORT_CAPTURE_PATH=str(output))
+    else:
+        command.append("--headless")
+    command.extend(["--main-pack", str(pack), "--script", str(script)])
+    # Running inside the checkout masks missing packed resources: FileAccess
+    # can read original .tres files from disk even when the PCK only has .remap.
+    with tempfile.TemporaryDirectory(prefix="the-tree-export-check-") as isolated:
+        result = subprocess.run(command, cwd=isolated, env=env, timeout=180)
+    return result.returncode
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())