Replace `time.Sleep(retryDelay)` in `waitForHealth` (container.go) and
`waitForAgentctlHealthWith` (executor_docker.go) with a cancelable
`select { <-ctx.Done() | <-time.After(retryDelay) }`. Also skip the
final retry's sleep — the loop only re-enters when `i+1 < maxRetries`,
so the extra delay was just added latency on aborted launches.
Cancellation now propagates within ≤500 ms instead of waiting for the
next probe iteration to observe `ctx.Err()`.
José Almeida
aaec9e878a