Benign Intervention

Benign Intervention is a companion quest in Fallout 4.

Detailed walkthrough

 * 1) Once Cait trusts the Sole Survivor enough she'll tell them about her history and her current struggles with addiction, then suggest going to Vault 95 to seek treatment.
 * 2) Head to Vault 95 near the middle of the land area on the south side of the map, southwest (and across the river) from Egret Tours Marina.
 * 3) The Gunners have claimed the vault, so the player character 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. Watch out for traps throughout the vault.
 * 4) Ahead there's a large room with several enemies, a Master level terminal blocks the door to the south that leads to the detox chamber. Alternately in the overseer's office in the upper west side, there's an unlocked terminal that can open the door.
 * 5) Once passing by the door there are several more Gunners in the cafeteria, go upstairs and around to the terminal, inside there's a Gunner commander, a turret and an active bottlecap mine on the desk.
 * 6) Talk to Cait, she has misgivings about the process. The player character will have 3 easy persuasion options, all of them give the same result. Once she gets into the extractor chair, activate the terminal and watch the chair work.
 * 7) Speak with Cait again once it's done and the quest will end.

Bugs

 * The quest might not trigger after Cait's dialogue. If that happens, you can workaround this by not allowing her to talk to you about it (choose the "Maybe Later" option). You need her to not be your companion but you can't dismiss her directly without triggering the dialog. Find another one of your companions, and ask them to join you. Send Cait on her way. As she is leaving, talk to her. This will trigger the dialogue again and this time the quest will show up in your quest log.
 * To trigger Cait's quest after the bugged conversation, you should:
 * Get rid of any companion (you can do this by talking to them and choosing appropriate dialogue branch),
 * Stand in front of Cait,
 * Open console,  by default, execute
 * You will be fast moved to a place near Vault 95 and "Benign Intervention" quest will immediately be triggered to start, so you can see it in your quest log.
 * Talk to Cait and make her to be your companion,
 * 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, you need to physically pass through the door leading to the Gunner commander. You may need to walk out and then back in if you use 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 you open the door/enter 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.