fed-sx-m1: Step 4f-consolidate — bootstrap:start/3 one-call boot + 10 tests

next/kernel/bootstrap.erl

@@ -5,7 +5,8 @@
          build_genesis/1, verify_genesis/2,
          cidhash_path/1, write_cidhash/2, read_cidhash/1,
          load_genesis/1, strip_sx_suffix/1,
-         populate_registry/0]).
+         populate_registry/0,
+         start/3]).
 
 %% Genesis bundle reader per design §12.2.
 %%
@@ -205,3 +206,18 @@ populate_entries(Kind, [{Name, Bytes} | Rest], Count) ->
     BaseName = strip_sx_suffix(Name),
     ok = registry:register(Kind, BaseName, Bytes),
     populate_entries(Kind, Rest, Count + 1).
+
+%% start/3 — one-call bring-up of the kernel substrate. Starts
+%% the registry gen_server, populates it from the canonical
+%% genesis bundle, then starts the nx_kernel gen_server with the
+%% supplied actor identity / key / state. Returns the nx_kernel
+%% Pid (gen_server start_link convention in this port returns the
+%% raw Pid, not {ok, Pid}).
+%%
+%% Tests + production bring-up share this entry point. The
+%% caller is still responsible for starting any application-level
+%% projections and wiring them via nx_kernel:with_projections/1.
+start(ActorId, KeySpec, ActorState) ->
+    registry:start_link(),
+    populate_registry(),
+    nx_kernel:start_link(ActorId, KeySpec, ActorState).