OptionalengineInternal seam for future profiles/per-engine knobs: when provided (and mode is 'full'), only registrations passing the predicate execute. Not surfaced in user-facing configuration.
OptionalmodeWhich startup profile to run. Defaults to 'full'. Resolve via ResolveStartupMode() so the env-var/config precedence chain behaves identically across entry points.
Options for StartupManager.Startup(). All fields optional; omitted ⇒ 'full' mode with no filter, i.e. pre-change behavior.