fed-sx-m2: Step 1a — nx_kernel per-actor bucket refactor + 17 tests

State shape becomes [{actors, [{Id, Bucket}, ...]}, {next_actor_seq, N}]
with ActorBucket = [{key_spec, KS}, {actor_state, AS}, {log, L},
{projections, [Name]}, {next_published, N}]. Pure-functional multi-
actor APIs (new/0, add_actor/4, has_actor/2, actors/1, actor_count/1,
publish/3, per-actor accessors, with_actor_projections/3) join the
legacy single-actor accessors, which now read from the first bucket.
Every M1 test continues to pass via bootstrap:start/3 -> new/3 ->
first-bucket lookup.

Local has_keyed/find_keyed/set_keyed/set_bucket helpers cover the
keyed-list ops since lists:keymember/keyfind aren't registered in
this substrate.

next/tests/nx_kernel_multi.sh 17/17. M1 nx_kernel-adjacent suites
green (bootstrap_start 10/10, nx_kernel_server 11/11, http_publish
10/10, smoke_app_pure 12/12, http_post_format 13/13, http_publish_fold
10/10, http_marshal 10/10). Erlang conformance 761/761 preserved.

Blockers entry added for pre-existing http_server_tcp.sh 0/5
regression (78eae9ef left dead helper references in runtime.sx:1593) —
substrate-side, out of m2 scope, confirmed pre-existing by reverting
1a's changes and re-running.

next/kernel/nx_kernel.erl

@@ -1,82 +1,232 @@
 -module(nx_kernel).
 -behaviour(gen_server).
--export([new/3, publish/2,
+
+%% Pure-functional API
+-export([new/0, new/3,
+         add_actor/4, has_actor/2, actors/1, actor_count/1,
+         publish/2, publish/3,
          actor_id/1, log_state/1, log_tip/1,
-         key_spec/1, actor_state/1, projections/1,
-         next_published/1, with_projections/2]).
+         key_spec/1, actor_state/1, projections/1, next_published/1,
+         actor_log_state/2, actor_log_tip/2,
+         actor_key_spec/2, actor_state/2, actor_projections/2,
+         actor_next_published/2, actor_bucket/2,
+         with_projections/2, with_actor_projections/3,
+         next_actor_seq/1]).
+
+%% gen_server API
 -export([start_link/3, publish/1, query/0, log_tip/0,
          with_projections/1, stop/0]).
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2]).
 
 %% Kernel orchestrator — the long-lived runtime state held by the
-%% running fed-sx instance. The HTTP layer (Step 8c-post-publish
-%% follow-up) will park this in a gen_server and dispatch the POST
-%% /activity request through `publish/2`.
+%% running fed-sx instance. Step 1 (m2) refactor: state is now
+%% per-actor bucketed so one kernel hosts any number of actors.
 %%
-%% State shape (property list):
-%%   [{actor_id, A},
-%%    {key_spec, KS},          % proplist: key_id / algorithm / value
-%%    {actor_state, AS},       % proplist: public_keys
-%%    {log, L},                % log:open/2 return value
-%%    {projections, [Name]},   % list of registered projection process names
-%%    {next_published, N}]     % monotonic counter we feed as :published
+%% New state shape (property list):
+%%   [{actors, [{ActorId, ActorBucket}, ...]},
+%%    {next_actor_seq, NextN}]
 %%
-%% Step 6c's stage_replay catches duplicates by `:id`; the `:id`
-%% is derived from the unsigned envelope contents. Same Request +
-%% same `:published` -> same CID, so the next_published counter
-%% gives every publish a distinct timestamp without needing a
-%% wall-clock BIF.
+%% ActorBucket = [{key_spec, KS},
+%%                {actor_state, AS},
+%%                {log, L},
+%%                {projections, [Name]},
+%%                {next_published, NextSeq}]
+%%
+%% Legacy single-actor accessors (actor_id/1, key_spec/1, etc.)
+%% continue to read from the first registered actor — keeps every
+%% pre-m2 test passing through bootstrap:start/3.
+%%
+%% next_actor_seq is a monotonic counter handed out to add_actor for
+%% future use (e.g. per-actor URL paths in Step 4). It's not yet
+%% read by the rest of the kernel.
+
+%% ── Pure-functional API ──────────────────────────────────────────
+
+new() ->
+    [{actors, []}, {next_actor_seq, 1}].
 
 new(ActorId, KeySpec, ActorStateProplist) ->
-    {ok, L0} = log:open(ActorId, base_stub()),
-    [{actor_id, ActorId},
-     {key_spec, KeySpec},
-     {actor_state, ActorStateProplist},
-     {log, L0},
-     {projections, []},
-     {next_published, 1}].
+    {ok, S} = add_actor(ActorId, KeySpec, ActorStateProplist, new()),
+    S.
 
-%% publish/2 — pure state transition. Returns either:
-%%   {ok, Result, NewState}   — log + counter advanced
-%%   {error, Reason, State}   — state unchanged on validation halt
-publish(Request, State) ->
-    P   = field(next_published, State),
-    Ctx = [{actor_id,    field(actor_id, State)},
-           {published,   P},
-           {key_spec,    field(key_spec, State)},
-           {actor_state, field(actor_state, State)},
-           {log,         field(log, State)},
-           {projections, field(projections, State)}],
-    case outbox:publish(Request, Ctx) of
-        {ok, Result, NewLog} ->
-            State1 = set(log, NewLog, State),
-            State2 = set(next_published, P + 1, State1),
-            {ok, Result, State2};
-        {error, Reason, _} ->
-            {error, Reason, State}
+add_actor(ActorId, KeySpec, AS, State) ->
+    Actors = field(actors, State),
+    case has_keyed(ActorId, Actors) of
+        true ->
+            {error, already_present};
+        false ->
+            {ok, L0} = log:open(ActorId, base_stub()),
+            Bucket = [{key_spec, KeySpec},
+                      {actor_state, AS},
+                      {log, L0},
+                      {projections, []},
+                      {next_published, 1}],
+            Seq = field(next_actor_seq, State),
+            State1 = set(actors, Actors ++ [{ActorId, Bucket}], State),
+            State2 = set(next_actor_seq, Seq + 1, State1),
+            {ok, State2}
     end.
 
-%% Accessors
+has_actor(ActorId, State) ->
+    has_keyed(ActorId, field(actors, State)).
 
-actor_id(State)        -> field(actor_id, State).
-key_spec(State)        -> field(key_spec, State).
-actor_state(State)     -> field(actor_state, State).
-log_state(State)       -> field(log, State).
-log_tip(State)         -> log:tip(field(log, State)).
-projections(State)     -> field(projections, State).
-next_published(State)  -> field(next_published, State).
+actors(State) ->
+    [Id || {Id, _Bucket} <- field(actors, State)].
+
+actor_count(State) ->
+    length(field(actors, State)).
+
+next_actor_seq(State) ->
+    field(next_actor_seq, State).
+
+actor_bucket(ActorId, State) ->
+    find_keyed(ActorId, field(actors, State)).
+
+%% publish/3 — per-actor publish.
+publish(ActorId, Request, State) ->
+    case actor_bucket(ActorId, State) of
+        {error, no_actor} ->
+            {error, no_actor, State};
+        {ok, Bucket} ->
+            P = field(next_published, Bucket),
+            Ctx = [{actor_id,    ActorId},
+                   {published,   P},
+                   {key_spec,    field(key_spec, Bucket)},
+                   {actor_state, field(actor_state, Bucket)},
+                   {log,         field(log, Bucket)},
+                   {projections, field(projections, Bucket)}],
+            case outbox:publish(Request, Ctx) of
+                {ok, Result, NewLog} ->
+                    B1 = set(log, NewLog, Bucket),
+                    B2 = set(next_published, P + 1, B1),
+                    NewState = set_bucket(ActorId, B2, State),
+                    {ok, Result, NewState};
+                {error, Reason, _} ->
+                    {error, Reason, State}
+            end
+    end.
+
+%% publish/2 — legacy single-actor publish; routes to first actor.
+publish(Request, State) ->
+    case actors(State) of
+        [] -> {error, no_actor, State};
+        [First | _] -> publish(First, Request, State)
+    end.
+
+with_actor_projections(ActorId, Names, State) ->
+    case actor_bucket(ActorId, State) of
+        {error, no_actor} ->
+            {error, no_actor};
+        {ok, Bucket} ->
+            B1 = set(projections, Names, Bucket),
+            {ok, set_bucket(ActorId, B1, State)}
+    end.
 
-%% with_projections — return a new state with :projections replaced.
 with_projections(Names, State) ->
-    set(projections, Names, State).
+    case actors(State) of
+        [] -> State;
+        [First | _] ->
+            {ok, NewState} = with_actor_projections(First, Names, State),
+            NewState
+    end.
 
-%% Internal
+%% Per-actor accessors
+
+actor_log_state(ActorId, State) ->
+    case actor_bucket(ActorId, State) of
+        {ok, B}     -> {ok, field(log, B)};
+        {error, _}  -> {error, no_actor}
+    end.
+
+actor_log_tip(ActorId, State) ->
+    case actor_log_state(ActorId, State) of
+        {ok, L}     -> log:tip(L);
+        {error, _}  -> nil
+    end.
+
+actor_key_spec(ActorId, State) ->
+    case actor_bucket(ActorId, State) of
+        {ok, B}     -> {ok, field(key_spec, B)};
+        {error, _}  -> {error, no_actor}
+    end.
+
+actor_state(ActorId, State) when is_list(State), is_atom(ActorId) ->
+    case actor_bucket(ActorId, State) of
+        {ok, B}     -> {ok, field(actor_state, B)};
+        {error, _}  -> {error, no_actor}
+    end.
+
+actor_projections(ActorId, State) ->
+    case actor_bucket(ActorId, State) of
+        {ok, B}     -> {ok, field(projections, B)};
+        {error, _}  -> {error, no_actor}
+    end.
+
+actor_next_published(ActorId, State) ->
+    case actor_bucket(ActorId, State) of
+        {ok, B}     -> {ok, field(next_published, B)};
+        {error, _}  -> {error, no_actor}
+    end.
+
+%% Legacy single-actor accessors — read from first bucket. Keeps
+%% every M1 test (smoke_app_pure, bootstrap_start, http_publish,
+%% nx_kernel_server, http_post_format) passing.
+
+actor_id(State) ->
+    case field(actors, State) of
+        []                        -> nil;
+        [{First, _Bucket} | _]    -> First
+    end.
+
+key_spec(State) ->
+    bucket_field(key_spec, State).
+
+actor_state(State) ->
+    bucket_field(actor_state, State).
+
+log_state(State) ->
+    bucket_field(log, State).
+
+log_tip(State) ->
+    log:tip(log_state(State)).
+
+projections(State) ->
+    case bucket_field(projections, State) of
+        nil -> [];
+        Ps  -> Ps
+    end.
+
+next_published(State) ->
+    bucket_field(next_published, State).
+
+%% ── Internal helpers ──────────────────────────────────────────────
 
-%% "base_stub" — placeholder base path for the in-memory log
-%% in v1 (the in-memory log ignores the base argument).
 base_stub() ->
     <<98,97,115,101,95,115,116,117,98>>.
 
+bucket_field(Key, State) ->
+    case field(actors, State) of
+        []                        -> nil;
+        [{_First, Bucket} | _]    -> field(Key, Bucket)
+    end.
+
+set_bucket(ActorId, NewBucket, State) ->
+    Actors = field(actors, State),
+    NewActors = set_keyed(ActorId, NewBucket, Actors),
+    set(actors, NewActors, State).
+
+set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)];
+set_keyed(_, _, []) -> [].
+
+has_keyed(_, []) -> false;
+has_keyed(K, [{K, _} | _]) -> true;
+has_keyed(K, [_ | Rest]) -> has_keyed(K, Rest).
+
+find_keyed(_, []) -> {error, no_actor};
+find_keyed(K, [{K, V} | _]) -> {ok, V};
+find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).
+
 field(K, [{K, V} | _]) -> V;
 field(K, [_ | Rest]) -> field(K, Rest);
 field(_, []) -> nil.
@@ -91,6 +241,10 @@ set(K, V, [P | Rest]) -> [P | set(K, V, Rest)].
 %% Steps 5b and 7b. Same port quirks: raw Pid return, no `?MODULE`
 %% macro, spawned processes don't persist across separate
 %% erlang-eval-ast calls — tests inline start_link with operations.
+%%
+%% Step 1a (m2) keeps the gen_server single-actor; multi-actor
+%% gen_server calls (publish_to/2, log_tip_for/1, ...) land in
+%% iteration 1b.
 
 start_link(ActorId, KeySpec, ActorStateProplist) ->
     Pid = gen_server:start_link(nx_kernel,