Add idempotent native release installer with external ASR boundary

scripts/sync-installer.py

@@ -0,0 +1,10 @@
+#!/usr/bin/env python3
+"""Developer helper: synchronize the standalone piped installer payload."""
+from pathlib import Path
+root = Path(__file__).resolve().parents[1]
+wrapper = root / "install.sh"
+header = wrapper.read_text().split("<<'PY'\n", 1)[0] + "<<'PY'\n"
+payload = (root / "scripts/install_payload.py").read_text()
+if "\nPY\n" in payload:
+    raise ValueError("heredoc delimiter appears in payload")
+wrapper.write_text(header + payload + "\nPY\n")