The ref doc for max_lease_duration does not describe what it is or how it is used, especially about how it interacts with ack deadlines.

Given that this is an important config setting for long-running tasks, we may want to provide more documentation here by showing its default value (is it 2 hours), and explaining whether max lease duration restrains ack deadline modification or ack deadline modification overwrites max lease duration when one configures both flow control settings and ack deadlines.