> How is the "world" model different from plain dependency injection?

In addition to what the other comment said, this "world" model is great for hermetic testing of complex code, LLM written or not. We've seen existing projects that intercept the OS level syscall for testing, replayability, etc. Building it into the language runtime, hopefully with better ergonomics from the start than a syscall, would be a welcome addition broadly.

Dependency injection provides the same hermetic-testing capability, so that's not really an answer to OP's question. Effect-as-world-model is, in this specific way, just a special argument slot that only accepts dependency-injected functions.

What effects provide beyond DI is entirely in their ability to abort (resume zero times) or (in the case of multi-shot effects) resume multiple times. An effect that resumes exactly once is structurally the same as a dependency injected lambda.