I suspect Svelte’s heavy lift with compile-time reactivity came largely from trying to infer "reactive intent" from standard JavaScript code. Since JS is so dynamic, the compiler had to rely on heuristics or strict assignment rules

Coi avoids this ambiguity because the compiler can definitively trace usage patterns. Since mut variables are explicitly declared, the compiler essentially just looks at where they are used in the view {} block to establish dependencies at compile time. This static analysis is precise and doesn't require the compiler to "guess" intent, effectively preserving the benefits of compile-time reactivity without the fragility found in dynamic languages