* fix(macos): bound websocket ping so a dropped pong cannot orphan its continuation
URLSession drops the pong handler entirely when a web socket task is cancelled or
closed mid-flight. The existing gate guarded a double resume but nothing guarded
zero resumes, so the checked continuation leaked, Swift logged CONTINUATION
MISUSE, and keepaliveLoop's await never returned - wedging the keepalive for the
lifetime of the process.
Race the ping against a deadline and reuse the gate so exactly one resume wins.
Cancellation of the deadline returns without resuming, otherwise a delivered pong
would race the gate and surface as a spurious timeout.
* fix(macos): reuse URLError(.timedOut) instead of a new public ping error
Periphery flags a public enum referenced only inside its own module as dead
code in the shared OpenClawKit intersection scan. URLError keeps the timeout
indistinguishable from a transport timeout for callers, which already handle
URLSession errors from every other path, and adds no public surface.
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