Ebrahim Raisi death: What is the procedure after Iranian president dies while in office?

"Iranian rescuers are trying to locate the crashed plane carrying Iranian President Ebrahim Raisi. The fate of those on board the plan continues to remain uncertain at this hour. How does the Iranian constitution seek to continue the leadership in case an Iranian President dies while in office and who comes next in the transition? […] Jason Brodsky, policy director at United Against Nuclear Iran, told a media outlet that the president of Iran is more of an "implementer" of policies rather than a "decision-maker". He noted that the core policies of the Islamic Republic would remain unchanged regardless of who is president."