engate-attach — typed attach lifecycle.

See engate-types for the philosophy + phase markers. This crate provides the runtime machinery: Producer / Consumer traits, the typestate-enforced Attach<P> value, the AttachBuilder, and the linear-ish History<S> handle.

Quick example

use engate_attach::{Attach, Producer, Consumer};

let attach = Attach::builder()
    .producer(my_producer)
    .consumer(my_consumer)
    .build()                   // -> Attach<Spawned>
    .subscribe()?              // -> Attach<Subscribed>, also returns History<S>
    .replay(history)?          // -> Attach<Synced>
    .start_live();             // -> Attach<Live>

// Only an Attach<Live> can render.
attach.run();

Why typestate over runtime FSM

A Result return + match on phase string would also work, but the compiler would let you write attach.replay() on a Subscribed that you forgot to subscribe() first. Typestate makes the malformed call a compile error: Spawned has no replay method; Subscribed has no start_live method. You CAN'T write the bug.