Looks nice! Some thoughts:

  const now = ctx.flag("now", bool); // type-safe flag access

This is type-safe, but only at run time. Since your flags are (or could be) known at compile time, it would be nice to have this throw a compile error if the type is invalid.

Or even better - fully lean into comptime and generate a struct so you can use field access without specifying a type:

  const now = ctx.flag.now;