Add watch/unwatch API to the actor system so actors can monitor each
other's liveness. When a watched actor dies (panic or stop), watchers
receive an ActorExited notification via on_actor_exit().
- ExitReason enum (Stopped, Panicked, NodeDown) and ActorExited struct
- ContextInner::watch()/unwatch() + Ctx typed wrappers
- ActorInterface::on_actor_exit() default method (system message fallback)
- WatchRegistry in worker with bidirectional tracking
- Death notification dispatch as phase 5b in tick_once
- Runtime-level watch for external callers
- 10 behavioral tests in tests/watch_api.rs
- Design documents for OS features in docs/os-design/
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Adds `crates/wasm-actor/` (swactor-wasm-actor), which embeds wasmtime-sandboxed
Wasm instances inside regular swactor actors. Messages flow as raw bytes through
the guest ↔ host contract (alloc/handle exports, swactor.send import). The host
drains an outbox after each handle call and routes messages via ctx.send().
Includes 3 no_std guest modules (echo, double, silent) and 7 integration tests
covering roundtrip delivery, binary fidelity, multi-send, error cases, engine
sharing, and native↔wasm interop.
Authored by Claude, lovingly guided by Zachery Aaron Shores-Chmielewski
