In reality while project does indeed have Servo in its dependencies it only uses it for HTML tokenization, CSS selector matching and some low level structures. Javascript parsing and execution, DOM implementation & Layout engine was written from scratch with only one exception - Flexbox and Grid layouts are implemented using Taffy - a Rust layout library.
So while “from scratch” is debatable it is still immensely impressive to be that AI was able to produce something that even just “kinda works” at this scale.
“From scratch” is inarguably wrong given how much third-party code it depends on. There’s a reasonable debate about how much original content there is but if I was a principal at a company whose valuation hinges on the ability to actually deliver “from scratch” for real, I would be worried about an investor suing for material misrepresentation of the product if they bought now and the value went down in the future.
I'd push back on the idea that all the agents did was glue dependencies together — the JS VM, DOM, CSS cascade, inline/block/table layouts, paint systems, text pipeline, chrome, and more are all being developed by agents as part of this project. There are real complex systems being engineered towards the goal of a browser engine, even if not fully there yet.