Is my 1-year-old Delonix Regia okay in this shallow pot with moss on top?

[Anthony_Jamez12]

The tree is about 6 inches tall and it's in a very shallow pot — around 3.5 inches long, 4.5 inches wide, and only 1.8 inches deep. It’s currently in a bonsai soil mix of akadama, lava rock, and pumice. I’ve also added some moss on top to help retain moisture and for the aesthetic.

He's been doing well the past month in his new pot.

 

[Shibui]

The answer, as usual, is "it depends"
Some questions to consider:
Can you maintain sufficient soil moisture through your dry season? I understand Houston can be quite dry at certain times of the year.
Will you fertilise regularly to maintain nutrition while regular watering leaches nutrients?
Will you be happy with a small, skinny tree in a pot for the next 20 years or would you prefer a more impressive trunk with some actual branches?

If you can maintain soil moisture and maintain plant nutrition your tree will survive. If you can't keep up with either the tree is not likely to survive. The small soil volume will definitely restrict growth as long as it's confined to such a small pot.