What is the ruling on the emission of semen without pleasure due to constipation, and does the ruling differ if a person intentionally causes it, or intentionally causes it for fear of temptation (fitna) and immorality (fahisha)?

The described scenario is not masturbation as long as it does not involve manipulating the penis to induce arousal. Masturbation is the expulsion of semen without intercourse, whether it is forbidden, such as inducing arousal with the hand, or permissible, such as with the wife's hand. If this act is done for pleasure, then it is the forbidden masturbation.