v0.4.0

Fixed

• invoke! inside #[effectful(..., send)] functions — previously failed to compile due to a compiler limitation (rust-lang/rust#100013) where the compiler could not prove that ForwardEffects::forward's return type was Send. Internally replaced with synchronous coproduct conversions (EmbedEffect/ProjectResume) that the compiler handles correctly.

• Sequential invoke! calls with mutable borrows — invoke! previously required sub-programs to borrow for the entire outer computation's lifetime, preventing patterns like invoke!(sub(&mut state)); state.mutate(); invoke!(sub(&mut state));. Sub-programs can now borrow from shorter-lived data than the outer program.

• invoke! with overlapping resume types — fixed an index inference bug where multiple effects sharing the same resume type (e.g., both resuming with ()) caused incorrect dispatch.

Changed

• Manual Effect impls require shorten_resume — the Effect trait now includes a shorten_resume method that witnesses the covariance of Resume<'r> in 'r. This is needed by invoke to safely shorten resume lifetimes when composing programs. The body is always just resume. The #[effect] macro generates it automatically, so this only affects hand-written impl Effect blocks.

• ForwardEffects trait removed — replaced internally by EmbedEffect and ProjectResume. This trait was not part of the public API.