fix subcommands in json model

lib/store.ml

@@ -308,6 +308,34 @@ let lookup_raw dirs command =
 let has_command dirs command =
   find_file dirs command <> None
 
+let subcommands_of dirs command =
+  let prefix = filename_of_command command ^ "_" in
+  let plen = String.length prefix in
+  let module SMap = Map.Make(String) in
+  let subs = ref SMap.empty in
+  List.iter (fun dir ->
+    if Sys.file_exists dir && Sys.is_directory dir then
+      Array.iter (fun f ->
+        if String.starts_with ~prefix f then
+          let base =
+            if Filename.check_suffix f ".json" then
+              Some (Filename.chop_suffix f ".json")
+            else if Filename.check_suffix f ".nu" then
+              Some (Filename.chop_suffix f ".nu")
+            else None in
+          match base with
+          | Some b ->
+            let rest = String.sub b plen (String.length b - plen) in
+            (* Only direct children: no further underscores *)
+            if not (String.contains rest '_') && String.length rest > 0 then
+              let name = rest in
+              if not (SMap.mem name !subs) then
+                subs := SMap.add name { name; desc = "" } !subs
+          | None -> ()
+      ) (Sys.readdir dir)
+  ) dirs;
+  SMap.fold (fun _ sc acc -> sc :: acc) !subs [] |> List.rev
+
 let all_commands dirs =
   let module SSet = Set.Make(String) in
   let cmds = ref SSet.empty in