Currently, it is possible to trigger a Flow (A) from a Flow (B). However, Flow A does not have a start trigger to only start when triggered from another Flow.
I know we can use the 'When a HTTP request is received' trigger and even the 'Flow button' but I have specific Flows that only run as subroutines for other Flows and I want to limit the possibility to inadvertently or maliciously start that subroutine.
My suggestion: create a 'When a Flow is triggered by another Flow' trigger action. Ideally, with the option to specify which Flow is allowed to start the subroutine for added insurance.