feat(tty): implement TtyBackend trait, TtyHandle, TtyControl, TtyParams, TtyError (ADR-053)
Implements the one-way-door backend inversion point in crates/alknet-tty/src/backend.rs:
- TtyBackend trait (#[async_trait]): allocate() + resource_id() default None
- TtyError enum (#[non_exhaustive]): AllocFailed, WaitFailed, Io, Backend
- TtyParams + TerminalParams (allocation request shapes)
- TtyHandle: stdin (AsyncWrite), stdout/stderr (Stream<Bytes>),
exit_code (BoxFuture<Result<i32,TtyError>>), control (Option<TtyControlHandle>)
- TtyControl trait (object-safe, NOT Clone) + TtyControlHandle newtype
(#[derive(Clone)] wrapping Arc<dyn TtyControl + Send + Sync>)
- From<NegotiateRequest> for TtyParams and From<TerminalParamsWire> for
TerminalParams (adapter uses these; no hand-rolled mapping)
- MockBackend (in-memory mpsc pipes + oneshot exit + MockControl) for
compile-check and adapter tests
- Unit tests: TtyControlHandle clone+delegation, MockBackend allocate/exit,
resource_id default, From<NegotiateRequest> mapping (pty + pipe modes)
TtyBackend trait doc carries REQ-TTY-01 (backends need not be natively
async); TtyHandle.exit_code doc carries the ADR-056 kill-on-Drop contract.
negotiation.rs carries minimal NegotiateRequest/TerminalParamsWire
placeholders (field set per tty-wire.md) so the From conversion compiles
before the negotiation task lands; that task replaces them with the full
framing machinery.
glm-5.2
b5834d3385