services.<TAG>.dl values only applied when the key was also set in the global dl: section (equality check against config.dl missed Click's declared defaults). Gate on Click's ParameterSource instead: CLI/env > service dl > global dl > defaults, converted via each option's own type.
- record parameter sources on serve's hand-built context so client values are never clobbered
- accept range/list as natural keys for range_/list_
- harden QualityList (YAML int) and SlowDelayRange (YAML bool) converts
