readLoop sent the response on the pending channel while holding c.mu. A misbehaving server sending a duplicate response for the same id would block on the buffered(1) channel under the lock, deadlocking all future dispatches. Use a non-blocking send (matching the notification path).
The goroutine parks in the blocking stderr.Read, so closing c.done does not interrupt it; termination relies on the read erroring at pipe EOF when the process is killed. The c.done select is only a best-effort fast path.
lukaszraczylo