Add supply auto-purchase and preserve save recovery state

tests/performance/test_digest_performance.gd

@@ -25,9 +25,11 @@ func _run() -> void:
 
 
 func _test_value_types() -> void:
+	# Escaped NUL was parsed as U+FFFD; keep identical values without import diagnostics.
+	# Runtime NUL-attempt coverage remains in _test_text_chunk_boundaries.
 	var values: Array = [
 		null, false, true, -9223372036854775807, 9223372036854775807,
-		0, 0.0, -0.0, -0.125, 1.25e100, "", "厨房\u0000🌳", &"", &"運搬",
+		0, 0.0, -0.0, -0.125, 1.25e100, "", "厨房" + String.chr(0xfffd) + "🌳", &"", &"運搬",
 		Vector2(-1.5, 2.25), Vector2i(-3, 7), Rect2(-1.5, 2.25, 3.5, 4.75),
 		Rect2i(-3, 7, 2, 8), Vector3(-1.5, 2.25, 3.5), Vector3i(-3, 7, 2),
 		Vector4(-1.5, 2.25, 3.5, 4.75), Vector4i(-3, 7, 2, 8), Color(0.25, 0.5, 0.75, 1),
@@ -53,7 +55,7 @@ func _test_dictionary_layouts() -> void:
 	# keep their type tags apart even when the textual schemas are identical.
 	for index in 60:
 		var row := {}
-		var keys: Array = ["z", "aa", "日本語", "a", "\u0000", "", "001"]
+		var keys: Array = ["z", "aa", "日本語", "a", String.chr(0xfffd), "", "001"]
 		if index % 2 == 1:
 			keys.reverse()
 		for key: String in keys: