WIP checkpoint: Client-side position sync + prediction/reconciliation

scripts/smoke_test_network_client.gd

@@ -73,6 +73,11 @@ func _run() -> void:
 	var reconcile_handler := func(err): reconciled_this_round = true; correction_seen = err
 	net.reconciled.connect(reconcile_handler)
 	for i in 60:
+		# Keep predicting (with no movement input) so the prediction buffer's
+		# latest entry actually reflects the desynced position -- without
+		# this, the buffer either empties out or keeps stale pre-desync
+		# entries, and _handle_snapshot has nothing real to compare against.
+		net.predict_and_send(1.0 / 30.0, 0.0, 0.0, false)
 		await process_frame
 		if reconciled_this_round:
 			break