TOKYO—Toyota Motor Corp. will restart domestic production from Wednesday after a cyberattack on a supplier ground the automaking giant’s factories to a one-day halt, sparking concerns about vulnerability in Japan Inc.’s supply chain. No information was available about who was behind the attack, or the motive. It came just after Japan joined Western allies in clamping down on Russia in response to the invasion of Ukraine, although it was not known whether the attack was related. Cybersecurity has emerged as a key area of concern in Japan, where government critics say responses to hacking threats have been hampered by a fractured approach, with an attack on a hitherto obscure supplier enough to bring one of the world’s mightiest manufacturers to a domestic standstill. Toyota’s production lines will be switched back on at its 14 factories across the country on Wednesday, it said in a statement. Tuesday’s suspension hit output of …