Crate engate_types 

engate-types — typed phase markers + traits for the engate attach primitive. The actual attach machinery lives in engate-attach; this crate is the small dependency-free contract so consumers can depend on shapes without pulling in statig / typed-builder.

Why

The bug class engate kills: a producer (PTY, WS, MQ, network) emits data BEFORE a consumer subscribes; subscribe returns only NEW data; the consumer’s local model stays empty even though the producer’s state is full. Today’s hand-wired attach paths in the pleme-io fleet (mado↔tear, kenshi↔testpod, hiroba clients, ayatsuri↔mado, namimado↔CDP) all suffer this class.

The fix: model attach as a 4-state typestate (Spawned → Subscribed → Synced → Live) where the consumer can only render from a Live value, Live can only be reached via Synced.start_live(), Synced can only be reached via Subscribed.replay(history), and history is a #[must_use] linear-ish handle that cannot be dropped without being consumed. Reaching the render path WITHOUT history is unrepresentable in the type system.

See pleme-io/CLAUDE.md task tracker (#123-#129) for the full M0-M6 roadmap.

Structs

EngateSpec

Declarative spec for one engate attach point. Authored either by hand in Rust (EngateSpec { ... }) or via tatara-lisp’s (defengate ...) form (M5.1 — #[derive(TataraDomain)] lands when tatara-lisp’s macro story is mature enough to consume this without a manual register() boilerplate dance).

Live

Live items from the producer are flowing into the consumer. This is the only phase from which render() is reachable. Construction gated on Synced.start_live() — reaching Live without going through Synced is impossible in the type system.

Spawned

Initial phase: producer has been identified (e.g. a pane id, a channel name) but no connection has been opened yet.

Subscribed

The consumer has registered with the producer’s live emission stream. No history has been replayed yet — calling render here would show an empty model even if the producer’s state is full.

Synced

Historical snapshot has been replayed into the consumer. The consumer’s local model now matches the producer’s state as of the snapshot. Live stream may have items queued but not yet forwarded.

TypePath

A crate + dotted type path. Two strings instead of one because the Nix side needs the crate name for the closure graph and the type path for the Rust import.

Enums

AttachError

Errors that can occur during an attach lifecycle.

Traits

Phase

Phase of an attach lifecycle. Marker only — carries no data.

Snapshot

Producer-side snapshot of current state. Whatever the consumer needs to bootstrap its local model to match the producer at attach time. For tear: a PaneSnapshot (grid + cursor + flags). For a WebSocket: the last N messages. For a Kubernetes log stream: the tail of stdout up to attach time.