[Bug] `context.watch()` is a silent no-op for a remote ref, so cross-node death watch never delivers `Terminated` despite the JSDoc promising it unconditionally

[pathosDev]

Problem

context.watch(remoteRef) is a silent no-op. Death watch across a cluster boundary does not exist, and nothing says so — ActorContext.watch's JSDoc promises unconditionally that a Terminated message is sent when the watched actor stops.

The consequence is that every supervision pattern built on death watch degrades silently the moment the watched actor is on another node: a watcher waiting for Terminated to trigger failover, replace a worker, or release a resource simply waits forever. Nothing logs, nothing throws, and it works perfectly in a single-node test.

Evidence

watch() registers the watcher only for a local ref:

src/internal/ActorCell.ts:494-503
  watch(ref: ActorRef): ActorRef {
    const key = ref.path.toString();
    if (this._watching.has(key)) return ref;
    this._watching.set(key, ref);
    if (ref instanceof LocalActorRef) {
      ref.getCell()._addWatcher(this.self);
    }
    return ref;
  }

For a RemoteActorRef the _watching map is updated and nothing else happens.

The system command that would carry a remote death notice has no producer anywhere in the repository. A repo-wide grep for watchNotify outside its own type declaration returns exactly two hits — a passing mention in a comment, and the handler:

src/ActorContext.ts:210:   * supervision, watchNotify) are NOT throttled — they always run
src/internal/ActorCell.ts:766:      .with({ kind: 'watchNotify' }, (signal) => this.onWatchNotify(signal))

src/cluster/RemoteActorRef.ts contains zero occurrences of watch or Terminated (grep count: 0), so there is no remote side either.

The contract as documented:

src/ActorContext.ts:126
   * Start death-watching an actor.  A Terminated message is sent when it stops.

Proposal

Two acceptable outcomes; the current one is neither.

1. Implement it. The receiving node registers a remote watcher, the owning node emits watchNotify over the wire when the watched actor terminates, and the watcher's node also synthesises Terminated when the owning node leaves or is downed — the second half is what makes it useful, since node loss is the case death watch exists for.
2. Refuse it loudly. watch() throws on a non-local ref with a message naming the limitation, and the JSDoc states the constraint.

A silent no-op behind an unconditional promise is the worst of the three, because it fails only in the environment the feature is for.

Acceptance sketch

• context.watch(remoteRef) either delivers Terminated when the remote actor stops, or throws with an actionable message.
• If implemented: a watcher receives Terminated when the owning node is downed, not only when the actor stops cleanly.
• ActorContext.watch's JSDoc matches whichever behaviour ships.
• A multi-node test covers the case — no test currently exercises watch across a node boundary.

Verification status

Found in the ten-lens production-readiness review of 2026-08-05 (v0.13.0) and re-verified before filing: confirmed by reading the cited lines and by repo-wide greps for watchNotify producers and for watch/Terminated in RemoteActorRef.ts. Not reproduced at runtime, because doing so requires a two-node cluster and the absence of a producer is already decisive.

Part of the production-readiness review batch — tracked in #913.

[pathosDev]

Correction: the evidence was read against a tree that predates 37 commits now on develop.

Filed from a worktree branched at 45b33d24; develop is now at 30e6a3a5. src/internal/ActorCell.ts has since taken 1ece6191, 4d56099e, b944c2e6 and 4e5b3274.

Nothing here is fixed. watch() is now at src/internal/ActorCell.ts:499-507 and still registers a watcher only for a LocalActorRef; watchNotify still has no producer anywhere in the repository — the only two hits remain the handler (now src/internal/ActorCell.ts:771) and the passing mention in src/ActorContext.ts:210. src/cluster/RemoteActorRef.ts is untouched and still contains zero occurrences of watch or Terminated.

Corrected citations: ActorCell.ts:494-503 → 499-507; ActorCell.ts:766 → :771. The two src/ActorContext.ts citations (:126, :210) are still exact.