Is it types? Are types the answer? Is it rust?
As time has gone on Rails has gotten better about this, but it still means that "your rails" and "my rails" are different enough that AI could easily get confused.
As you say, the other aspect is the intense dynamism which works against AI, which again prefers to have everything explicit and reasonable about from the text.
So I ended up going back to Javascript after a brief 12 year digression into Ruby. I still love Ruby but it's just not the right language for the current environment and team structures - typescript is "worse is better" in the right ways that it's a much better choice for both frontend/backend being the same and better type systems.
However Rust has one serious problem, BUILDS. It’s slow and it takes up a ton of space and memory. You will be working around this on any sizeable codebase. Using cargo check to ration your compiles, a dedicated build box, etc. Now imagine you're using it for a web application with compiled maud templates... you're potentially waiting minutes to see your changes.
If we accept that over half of the people building with rust are using agents (I'm sure this is much higher in reality), then you should also accept that there is a ton of time and resources spent on building / compiling. Optimizing this should probably be a top priority. They need someone who will be fanatical about shaving time and memory use from the build process.
Maybe there will be one day, but what are the odds that it will meaningfully move the needle for existing platforms such that manual code review is unnecessary? "Blindly trust the output" is not a feasible security posture today.