Benign Intervention

Benign Intervention is a companion quest in Fallout 4.

Quick walkthrough

 * 1) Bring Cait to Vault 95
 * 2) Locate the clean room
 * 3) Speak to Cait
 * 4) Wait for Cait to get in the clean room chair
 * 5) Cure Cait's addiction
 * 6) Speak to Cait

Detailed walkthrough

 * 1) Once Cait trusts you enough she'll tell you about her history and her current struggles with addiction, then suggest going to Vault 95 to seek treatment.
 * 2) Head to Vault 95 in the south west corner of the map.
 * 3) The Gunners have claimed the vault, so you'll need to fight your 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's several more gunners in the cafeteria, go upstairs and around to the terminal, inside there's a Gunner Commander, turret and an active bottlecap mine on the desk.
 * 6) Talk to Cait, she has misgivings about the process.  You'll have 3 easy persuasion options, all of them give the same result.  Once she gets into the chair activate the terminal and watch the chair work.
 * 7) Speak with Cait again once it's done and the quest will end.

Bugs
To trigger Cait quest AFTER the bugged conversation, you should: 1. Get rid of any companion (you can do this by talking to them and choosing appropriate dialogue branch), 2. Stand in front of Cait, 3. Open console,   by default, execute 4. 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. As for me, at that moment Cait wasn't near me, she appeared 5-10 seconds later when I moved a bit from the place fast travel dropped me, 5. Talk to Cait and make her to be your companion, 6. 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.
 * 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 dialog again and this time the quest will show up in your quest log.
 * 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.
 * Make sure Cait isn't in power armor before opening the door to the clean room. It will disappear as she has to be out of it in order to progress. (She may simply exit it but she seems to have disappeared instead?)
 * The elevator tends to get stuck upon entering it and activating the button. To fix this, simply restart the game.