Answer architecture round 1: Main draws the CLI's default seed and passes it to run, New names every option mistake at once, dataGiven says what it is, and the docs drop seeded where every sequence is

cli/cli.go

@@ -320,7 +320,7 @@ func (in invocation) check(name string) error {
 	return nil
 }
 
-func (in invocation) options(modules []fs.FS) []fejkdata.Option {
+func (in invocation) options(modules []fs.FS, systemSeed uint64) []fejkdata.Option {
 	if in.noShipped {
 		modules = nil
 	}
@@ -330,7 +330,7 @@ func (in invocation) options(modules []fs.FS) []fejkdata.Option {
 	}
 	seed := in.seed
 	if !in.seeded {
-		seed = rand.Uint64()
+		seed = systemSeed
 	}
 	return append(opts, fejkdata.WithSeed(seed))
 }
@@ -572,7 +572,7 @@ func Main(modules ...fs.FS) int {
 	if fi, err := os.Stdin.Stat(); err == nil && fi.Mode()&os.ModeCharDevice != 0 {
 		stdin = nil
 	}
-	return run(commandName(os.Args[0]), modules, os.Args[1:], stdin, os.Stdout, os.Stderr)
+	return run(commandName(os.Args[0]), modules, os.Args[1:], rand.Uint64(), stdin, os.Stdout, os.Stderr)
 }
 
 // commandName is the name the command runs under: the file arg0 names, less a Windows
@@ -588,9 +588,9 @@ func commandName(arg0 string) string {
 	return name
 }
 
-// run is Main over the given streams, run as the command name. A nil stdin is a terminal,
-// which holds no template.
-func run(name string, modules []fs.FS, args []string, stdin io.Reader, stdout, stderr io.Writer) int {
+// run is Main over the given streams, run as the command name, seeded by systemSeed where
+// no --seed is given. A nil stdin is a terminal, which holds no template.
+func run(name string, modules []fs.FS, args []string, systemSeed uint64, stdin io.Reader, stdout, stderr io.Writer) int {
 	in, err := parseArgs(args)
 	if err != nil {
 		return misuse(stderr, name, err)
@@ -613,7 +613,7 @@ func run(name string, modules []fs.FS, args []string, stdin io.Reader, stdout, s
 			return fail(stderr, name, err)
 		}
 	}
-	f, err := fejkdata.New(in.options(modules)...)
+	f, err := fejkdata.New(in.options(modules, systemSeed)...)
 	if err != nil {
 		return fail(stderr, name, err)
 	}