diff --git a/game/tests/test_two_instances.gd b/game/tests/test_two_instances.gd
index 965dd2d..2d9b897 100644
--- a/game/tests/test_two_instances.gd
+++ b/game/tests/test_two_instances.gd
@@ -18,6 +18,9 @@ func test_a_guest_in_another_process_stays_in_lockstep() -> void:
 	host.options.port = 0
 	host.listen_address = "127.0.0.1"
 	check(host.play(true), "the world opens")
+	# The host's clock waits for the guest, so that a slow start of the second
+	# process cannot use up the ticks before UNTIL.
+	host.clock.paused = true
 
 	var report_path := directory.path_join("guest.json")
 	var arguments := PackedStringArray([
@@ -63,3 +66,30 @@ func test_a_guest_in_another_process_stays_in_lockstep() -> void:
 	host.link.link.close()
 	host.free()
 	TestFiles.remove_dir(directory)
+
+
+func test_a_guest_bot_that_cannot_write_its_report_still_ends() -> void:
+	var directory := TestFiles.temporary_dir("bot-report")
+	var arguments := PackedStringArray([
+		"--headless",
+		"--path", ProjectSettings.globalize_path("res://"),
+		"--log-file", ProjectSettings.globalize_path(directory.path_join("bot.log")),
+		"-s", "res://tools/guest_bot.gd",
+		"--",
+		# An address that cannot be read ends the session at once.
+		"--join=host:port",
+		"--storage=" + directory.path_join("bot"),
+		# A folder cannot be opened as the report file.
+		"--out=" + ProjectSettings.globalize_path(directory),
+	])
+	var process := OS.create_process(OS.get_executable_path(), arguments)
+	check(process > 0, "the bot starts")
+	var started := Time.get_ticks_msec()
+	while OS.is_process_running(process) and Time.get_ticks_msec() - started < PATIENCE_MSEC:
+		await tree.process_frame
+	var ended := not OS.is_process_running(process)
+	if not ended:
+		OS.kill(process)
+	check(ended, "the bot ends")
+	check_eq(OS.get_process_exit_code(process), 1, "and reports a failure")
+	TestFiles.remove_dir(directory)
diff --git a/game/tools/guest_bot.gd b/game/tools/guest_bot.gd
index 55df730..786459d 100644
--- a/game/tools/guest_bot.gd
+++ b/game/tools/guest_bot.gd
@@ -24,7 +24,9 @@ func _run() -> void:
 	var report := {"error": "the host did not answer"}
 
 	var main: Node = load("res://main.tscn").instantiate()
-	main.storage_dir = settings.get("--storage", "user://bot")
+	# Never the player's own folder, even for an empty --storage=.
+	var storage: String = settings.get("--storage", "")
+	main.storage_dir = storage if not storage.is_empty() else "user://bot"
 	main.command_line = PackedStringArray(["--join=" + settings.get("--join", ""), "--name=Bot"])
 	root.add_child(main)
 
@@ -50,10 +52,16 @@ func _run() -> void:
 			}
 			break
 
-	var file := FileAccess.open(settings.get("--out", "user://bot.json"), FileAccess.WRITE)
-	file.store_string(JSON.stringify(report))
-	file.close()
+	# The bot ends in every case, even if the report cannot be written, so that
+	# it never outlives the test that started it.
+	var path: String = settings.get("--out", "user://bot.json")
+	var file := FileAccess.open(path, FileAccess.WRITE)
+	if file == null:
+		push_error("the report cannot be written to %s: %s" % [path, error_string(FileAccess.get_open_error())])
+	else:
+		file.store_string(JSON.stringify(report))
+		file.close()
 	main.notification(Node.NOTIFICATION_WM_CLOSE_REQUEST)
 	root.remove_child(main)
 	main.free()
-	quit(0 if not report.has("error") else 1)
+	quit(0 if file != null and not report.has("error") else 1)