Benign Intervention

Benign Intervention is a companion quest for Cait in Fallout 4.

Detailed walkthrough
Once Cait trusts the Sole Survivor enough (requires 750 affinity), she will tell them about her history and current struggles with addiction. She will then suggest going to Vault 95 to seek treatment since her addiction has progressed to the point that standard treatments will no longer work. Vault 95 is to the west and just slightly north of Somerville Place.

The Gunners have claimed the vault, so the Sole Survivor will need to fight their way in. The room on the right after leaving the elevator (locked with an Advanced lock) has a terminal that can be used to deactivate some turrets ahead. Additionally, there are traps throughout the vault. Ahead is a large room with several enemies, and a Master level terminal blocks the door to the south that leads to the detox chamber.

Alternatively, in the overseer's office on the upper west side, there is an unlocked terminal that can open the door. Once passing through the door, several Gunners are found in the cafeteria. Go upstairs and around to the terminal to unlock the waiting area before the cleanroom. Inside the side room are a Gunner commander, a turret, and an active bottlecap mine on the desk.

Before entering the detox chamber, talk to Cait, who has misgivings about the process. There will be three Easy persuasion options, all of which give the same result. Once she gets into the extractor chair, activate the terminal and watch the chair work. Speak with Cait again once it is done and the quest will end.

Bugs

 * The quest might not trigger after Cait's dialogue. If that happens, one can work around this by not allowing her to talk about it (choose the "Maybe Later" option). At this point, she will need to leave the player character's party but can't be dismissed directly without triggering the dialogue. Find another companion and ask them to join. Send Cait on her way, and as she is leaving, talk to her. This will trigger the dialogue again and this time, the quest will show up in the quest log.
 * To trigger Cait's quest after the bugged conversation, one can also:
 * Get rid of any companion (do this by talking to them and choosing the appropriate dialogue branch),
 * Stand in front of Cait,
 * Open console and execute.
 * The player character will be teleported to a location near Vault 95 and "Benign Intervention" quest will immediately be triggered to start, so one can see it in their quest log.
 * Talk to Cait and add her to the player character's party,
 * From this point you can be sure that if you follow all other advises in this section you will not encounter any bugs during the "Benign Intervention" quest.
 * To complete the "Find the Clean Room" objective, one will need to physically pass through the door leading to the Gunner commander. One may need to walk out and then back in if using V.A.T.S. or a perk like Blitz to enter the room rather than by walking through the door.
 * The elevator tends to get stuck upon entering it and activating the button. To fix this, simply restart the game.
 * If Cait is wearing power armor when opening the door and entering the waiting room outside the Clean Room, it will disappear and not be recoverable after the procedure is finished. Have her get out of the suit outside of that area before proceeding.
 * If starting the quest while already in Vault 95 via normal means, it will become bugged to where returning to the entrance does not go beyond the first stage.