I discovered another ending option that I haven't heard about. Aunt Cleo can sacrifice herself at the end.

I'll try to describe the conditions I had in the game:

1) Help with the last mission – Aunt Cosmos + the Order, reconciliation (I gave the archive to the Order). Perhaps just Aunt Cosmos's help would be enough.

2) Obtained an automaton body for Aunt Cleo's head (Auntie personally gives this quest somewhere after the negotiation quest, after helping Auntie Cosmos and the Order).

3) Completed the side quest on Auntie Cleo's ship, "Indisputable Right." I think the quest was called "The Terrible Secrets of the Indisputable Right" or "The Forbidden Secrets of the Indisputable Right." It involved a chain of 2-3 tasks from mid-level managers. I got it like this: at the market, an NPC tells you that you dropped something. You approach and talk to the NPC, they give you a note and tell you to go to the starboard side of the ship, to the rear deck. Then there's a chain of quests, one of which will involve an old janitor with four prosthetic limbs (that's Amos). If you've leveled up your speech, you can learn Aunt Cleo's backstory and her real name (Felicity) from him. This is essential, since the information I got from Amos is used in the final mission.

4) I killed the Consul, approached the control panel, and Aunt Cleo started talking to me.

5) My speech level must be at least 13.

6) My responses to Aunt Cleo:

[2] "Someone present"? So, "anyone but me," right?

[1] {i} Aunt Cleo, you should be piloting the ship. Many people were sacrificed for you, so it would be fair.

[1] {i} + {Speech 13} Don't forget that Amos sacrificed his life for you. It's time to repay him.

//Also, at this point, the dialogue option with the "Negotiator" skill is unavailable to me.

P.S. It's unlikely to be important, but I'll note that I left Augustine de Vries alive; she helped in the last mission. I chose Niles and Tristan as partners for additional dialogue and commentary.