[Bug] An actor that throws in `onReceive` is restarted with no log output at any level, so a crash-looping actor is invisible in production

[pathosDev]

Problem

An actor that throws in onReceive and is restarted by its supervisor produces zero log output at any level. Not a warning, not a debug line — nothing. A crash-looping actor in production is invisible: the only residual signals are actor_restarted_total (unlabelled, in a registry that is a no-op unless someone called .enable() in code) and an ActorRestarted event on a stream that nothing in src/ subscribes to.

ActorCell.ts contains six log calls across 1272 lines, and an ordinary actor's failure path passes through none of them.

Evidence

The catch hands the cause to the parent and logs nothing:

src/internal/ActorCell.ts:1030-1037
      } catch (e) {
        const err = e instanceof Error ? e : new Error(String(e));
        failure = err;
        if (span) {
          span.recordException(err);
          span.setStatus('error', err.message);
        }
        this.failToParent(err, message);

failToParent logs only when there is no parent — i.e. only for the root guardian:

src/internal/ActorCell.ts:1107-1119
  private failToParent(cause: Error, message?: unknown): void {
    this.mailbox.suspend();
    if (this.state === 'running') this.state = 'suspended';
    for (const child of this._children.values()) child.enqueueSystem({ kind: 'suspend' });

    if (this._parent) {
      this._parent.enqueueSystem({ kind: 'failure', cause, child: this.self, message });
    } else {
      // Root guardian failed — log and terminate the system.
      this.log.error(`Guardian ${this.path} failed; terminating system`, cause);

onFailure logs only once the restart threshold is exceeded (:1154), and onRecreate (:914) logs nothing. The complete set of log calls in the file is lines 622, 810, 874, 932, 1116, 1154.

Reproduced with a logger injected via ActorSystemOptions at LogLevel.Trace, for three crashes and three restarts:

log lines mentioning the crash: []
total log lines captured: 0

Proposal

Log the failure where it happens. One this.log.error in failToParent carrying the cause, its stack, the actor path and the failing message's type, plus one line in onRecreate naming the directive taken. That is roughly five lines and it converts an invisible crash loop into an alertable one.

Rate-limiting is worth considering for a hot loop, but silence is not the right default — the current behaviour means the first thing an operator learns about a failing actor is a downstream symptom.

Acceptance sketch

• An unhandled throw in onReceive produces an ERROR line with the cause, the stack, the actor path and the failing message type.
• The supervision directive taken (Restart / Stop / Resume / Escalate) appears in the log.
• actor_restarted_total carries an actor-class label so the metric can answer "which actor is restarting" (see [Feature] Stock metric actor_mailbox_dropped_total labels by actor path — unbounded cardinality #658/[Security] actor_mailbox_dropped_total carries a dynamic path label that under sharding derives from a remote-supplied entity id, so a remote party mints permanent, never-evicted metric series #745 for the cardinality constraint on path).
• A test asserts that a crashing actor emits at least one ERROR line.

Verification status

Found in the ten-lens production-readiness review of 2026-08-05 (v0.13.0) and re-verified before filing: reproduced by execution with a spy logger at trace level; the log-call inventory above is a complete grep of this.log.* in ActorCell.ts.

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. The failure path is still silent, and the log inventory still has six entries — the file is now 1357 lines, not 1272, and every line number in the issue is stale:

cited	now
the catch that hands the cause to the parent, 1030-1037	1085-1092
failToParent, 1107-1119	1162-1174
the complete set of this.log.* calls: 622, 810, 874, 932, 1116, 1154	627, 835, 899, 962, 1171, 1209
the threshold-exceeded log.warn in onFailure, :1154	:1209
onRecreate, :914	:947

1ece6191 split onRecreate into onRecreate + completeRecreate; neither half logs the directive taken, so the second half of the proposal is untouched as well.