Value semantics with reference counting, no borrow checker

Oska guarantees memory safety through value semantics and automatic reference counting:

• There are no lifetimes or borrow checker.
• There are no shared mutable references, so reference cycles can't form and no cycle collector is needed.
• A var is mutated in place when its reference count is 1 and copied on write otherwise.

The research behind this design (findings 1 and 8) requires memory safety, but not any particular mechanism for it. We want signatures to describe authority (capabilities), not lifetimes. We also want to avoid the borrow-checker compile-fix loop for agents. That second point is a judgment call; it has not been measured.

Considered options

• Ownership and borrowing (Rust). Rejected. Lifetimes make signatures noisier, and borrow errors make agents iterate more.
• Tracing GC. Not chosen. Reference counting without cycles is simpler and its performance is predictable.
• Regions. Not chosen. Too novel to rely on, given models have little training data for them.

Consequences

Graph-shaped data has to use IDs or arena-style collections instead of pointers.

Mutation goes through mutating methods (fn push(var self, x: T)), which can only be called on var bindings. No parameter other than self can be mutated, so all other data has to flow out through return values.