Book about a boy in a science fantasy world who lives in a tree and accepts a job to steal an object from the royal family

Question

I'm looking for a book and the plot goes something like this: there's a boy who lives with his mom and sister, they're relatively poor and live in a small apartment genetically made out of a live tree. There are multiple worlds all connected by a train track with trains with consciousness and feelings piloting the track.

To get to the main plot, the kid is offered a job by a doctor/scientist with a female robot to steal an object from a royal family by pretending to be a relative. They succeed at stealing it, but while escaping in a space pod, the robot girl is launched away into space; he fell in love with the robot and he is able to escape and give the doctor the object, but the kid asks the doctor to save the robot which he fell in love with.

My memory is a little foggy here, but he somehow saved the robot, and I forgot what happened at the end, but they open a portal and that's how it ended. I read this book about 2-3 years ago on an iPad if that helps.

Answer 1

Railhead (2015) by Philip Reeve.

From Goodreads:

Come with me, Zen Starling, she had said. The girl in the red coat. But how did she know his name? The Great Network is a place of drones and androids, maintenance spiders and Station Angels. The place of the thousand gates, where sentient trains criss-cross the galaxy in a heartbeat. Zen Starling is a petty thief, a street urchin from Thunder City. So when mysterious stranger Raven sends Zen and his new friend Nova on a mission to infiltrate the Emperor's train, he jumps at the chance to traverse the Great Network, to cross the galaxy in a heartbeat, to meet interesting people - and to steal their stuff. But the Great Network is a dangerous place, and Zen has no idea where his journey will take him.

One of the reviews mentions:

Zen Starling makes his way by petty thievery. He lives with his older sister and his mother, who appears to be a paranoid schizophrenic. [...]

The primary 'gimmick' here is that easy, casual travel between worlds has been made possible by a network of trans-dimensional trains. No one really knows how they work, and the network's origin is shrouded in mystery - but they're a part of daily life that is taken for granted. So Zen can steal a necklace on one world, hop a train, and be back for dinner in another galaxy on time.

This other review has the tree house:

In the distant future, humanity has terraformed and colonized dozens of planets across the galaxy. We grow bio-architecture from genetically engineered plants, fight humanoid robots for employment, access the Datasea with the blink of an eye, and are policed by obedient drones.

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Found with the Google query scifi book sentient trains robot steal site:goodreads.com/book.