#2982 Forward held-lock identity over --server so a loopback nested swamp does not wait on its caller's lock

Follow-up to swamp-club#2955. A step of a run hosted by swamp serve (holding per-model lock nonce A under serve's pid) can run swamp model method run --server back into the same serve. Serve runs that request in its own held-lock scope, so a nested structural swamp spawned by that method's shell inherits only the new run's lock for serve's pid and waits on lock A. Step A waits on the client, the client waits on the server run, and the server run waits on the child, until SWAMP_LOCK_TIMEOUT_MS. Process ancestry cannot see a causal chain that passes through a WebSocket request. Before #2955 the pid-only skip let this through. Direction: the client forwards its inherited SWAMP_LOCK_HOLDER_TOKENS entry for the server's pid in the request payload, and serve seeds the run's scope with it after validating it. #2955 documents this as a known limitation.