TimedOut

No verdict — neither ResumeAck nor Reject — arrived within HeartbeatConfig.resumeTimeout.

The host is unreachable right now: it is gone, the link is black-holed, or the reply was lost. Not a refusal — deliberately distinct from WindowClosed, which conflates "expired" with "not yet open" (#1571); folding a silent host into that pile would hide a fourth, honest outcome. A later attempt with the same credentials may still succeed once the host is reachable again, so callers (and the internal auto-reconnect loop) treat it as a transient retry signal, not a terminal verdict.