fed-sx-m2: Step 11b — Announce + Endorse projection folds + 19 tests

Two new projection modules for the rich verbs landed in Step 11a:

  next/kernel/announce_state.erl
    Per-target-Cid announcer set.
    State: [{TargetCid, [AnnouncerActorId, ...]}, ...]
    Set semantics — duplicate Announce by the same actor on the
    same target is a no-op.

    Public API:
      new/0, fold/2, fold_fn/0
      announcers_for/2, announce_count/2, announced_cids/1
      has_announced/3

  next/kernel/endorsement_state.erl
    Per-target-Cid + per-kind + per-actor endorsement counter.
    State: [{TargetCid, [{Kind, [{ActorId, Count}, ...]}, ...]}, ...]
    Additive semantics — re-endorse by the same actor under the
    same kind bumps the counter. Undo{Endorse} retraction defers
    to a follow-up.

    Public API:
      new/0, fold/2, fold_fn/0
      counters_for/2, total_for/2, kinds_for/2
      endorsers_for/3, has_endorsed/4

Both fold_fn/0 returns a 2-arity Erlang fun for
projection:start_link/3 (same plug shape as actor_state /
follower_graph / delivery_state). Non-matching activity types
pass through unchanged.

Read-side accessors cover both enumeration (announcers_for,
endorsers_for) and predicates (has_announced, has_endorsed) so
the feed/timeline projection layer doesn't have to re-implement
that logic on every consumer.

19/19 in next/tests/rich_verbs.sh:

  announce_state:
    - new/0 -> []
    - Announce -> announcer added
    - Two announces same target -> both in set
    - Duplicate announce by same actor -> no-op
    - announce_count + announced_cids
    - has_announced predicate
    - fold_fn/0 is fun/2
    - Non-Announce activity passes through

  endorsement_state:
    - new/0 -> []
    - Endorse -> counter 1
    - Two likes by different actors -> total 2
    - like + share -> two kinds tracked
    - endorsers_for(Cid, Kind)
    - has_endorsed predicate
    - fold_fn/0 is fun/2
    - Non-Endorse activity passes through
    - Same actor endorsing twice -> total = 2 (additive)

Conformance preserved at 761/761.

next/kernel/announce_state.erl

@@ -0,0 +1,79 @@
+-module(announce_state).
+-export([new/0, fold/2, fold_fn/0,
+         announcers_for/2, announce_count/2, announced_cids/1,
+         has_announced/3]).
+
+%% Announce-fanout projection. Folds Announce activities into a
+%% per-target-Cid set of announcer ActorIds so projections can
+%% answer "who re-broadcast this activity" / "how many announces
+%% does this Note have" / "what activities has X announced".
+%%
+%% Announce envelope shape (per next/genesis/activity-types/announce.sx):
+%%   [{type, announce},
+%%    {actor, AnnouncerActorId},
+%%    {object, TargetCidBinary},
+%%    ...]
+%%
+%% State shape:
+%%   [{TargetCid, [Announcer1, Announcer2, ...]}, ...]
+%%
+%% Set semantics — the same actor announcing the same target twice
+%% is a no-op (already in the list). Undo{Announce} retraction
+%% defers to a follow-up.
+
+new() -> [].
+
+fold_fn() ->
+    fun (Activity, State) -> fold(Activity, State) end.
+
+fold(Activity, State) ->
+    case envelope:get_field(type, Activity) of
+        {ok, announce} -> fold_announce(Activity, State);
+        _              -> State
+    end.
+
+fold_announce(Activity, State) ->
+    case {envelope:get_field(actor, Activity),
+          envelope:get_field(object, Activity)} of
+        {{ok, Actor}, {ok, Cid}} -> add_announcer(Cid, Actor, State);
+        _                        -> State
+    end.
+
+add_announcer(Cid, Actor, State) ->
+    Current = case find_keyed(Cid, State) of
+        {ok, Set} -> Set;
+        _         -> []
+    end,
+    case contains(Actor, Current) of
+        true  -> State;
+        false -> set_keyed(Cid, Current ++ [Actor], State)
+    end.
+
+%% ── Read-side accessors ───────────────────────────────────────
+
+announcers_for(Cid, State) ->
+    case find_keyed(Cid, State) of
+        {ok, Set} -> Set;
+        _         -> []
+    end.
+
+announce_count(Cid, State) -> length(announcers_for(Cid, State)).
+
+announced_cids(State) -> [C || {C, _} <- State].
+
+has_announced(Actor, Cid, State) ->
+    contains(Actor, announcers_for(Cid, State)).
+
+%% ── Internal ──────────────────────────────────────────────────
+
+contains(_, []) -> false;
+contains(X, [X | _]) -> true;
+contains(X, [_ | Rest]) -> contains(X, Rest).
+
+find_keyed(_, []) -> {error, not_found};
+find_keyed(K, [{K, V} | _]) -> {ok, V};
+find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).
+
+set_keyed(K, V, []) -> [{K, V}];
+set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)].

next/kernel/endorsement_state.erl

@@ -0,0 +1,118 @@
+-module(endorsement_state).
+-export([new/0, fold/2, fold_fn/0,
+         counters_for/2, total_for/2, kinds_for/2,
+         endorsers_for/3, has_endorsed/4]).
+
+%% Endorsement counter projection. Folds Endorse activities into a
+%% per-target-Cid + per-kind counter so projections can serve
+%% "how many likes does this Note have" / "list everyone who shared
+%% this Announce" queries.
+%%
+%% Endorse envelope shape (per next/genesis/activity-types/endorse.sx):
+%%   [{type, endorse},
+%%    {actor, ActorId},
+%%    {object, TargetCidBinary},
+%%    {kind, KindAtomOrBinary},
+%%    ...]
+%%
+%% State shape:
+%%   [{TargetCid, [{Kind, [{ActorId, Count}, ...]}, ...]}, ...]
+%%
+%% Each ActorId can endorse the same target multiple times under
+%% the same kind (e.g. like → unlike → like → ...); the counter
+%% tracks how many *net* endorsement events fired. Step 11b ships
+%% the additive counter only; the unlike / un-endorse semantics
+%% (Undo{Endorse}) and reaction-toggling defer to a follow-up.
+
+new() -> [].
+
+fold_fn() ->
+    fun (Activity, State) -> fold(Activity, State) end.
+
+fold(Activity, State) ->
+    case envelope:get_field(type, Activity) of
+        {ok, endorse} -> fold_endorse(Activity, State);
+        _             -> State
+    end.
+
+fold_endorse(Activity, State) ->
+    case {envelope:get_field(actor, Activity),
+          envelope:get_field(object, Activity),
+          envelope:get_field(kind, Activity)} of
+        {{ok, Actor}, {ok, Cid}, {ok, Kind}} ->
+            bump(Cid, Kind, Actor, State);
+        _ ->
+            State
+    end.
+
+bump(Cid, Kind, Actor, State) ->
+    KindMap = case find_keyed(Cid, State) of
+        {ok, KM} -> KM;
+        _        -> []
+    end,
+    ActorMap = case find_keyed(Kind, KindMap) of
+        {ok, AM} -> AM;
+        _        -> []
+    end,
+    Current = case find_keyed(Actor, ActorMap) of
+        {ok, N} -> N;
+        _       -> 0
+    end,
+    ActorMap1 = set_keyed(Actor, Current + 1, ActorMap),
+    KindMap1  = set_keyed(Kind, ActorMap1, KindMap),
+    set_keyed(Cid, KindMap1, State).
+
+%% ── Read-side accessors ───────────────────────────────────────
+
+%% counters_for(Cid, State) -> [{Kind, TotalCount}, ...]
+%% Sum per-kind across all endorsers.
+
+counters_for(Cid, State) ->
+    case find_keyed(Cid, State) of
+        {ok, KindMap} ->
+            [{K, sum_counts(AM)} || {K, AM} <- KindMap];
+        _ -> []
+    end.
+
+total_for(Cid, State) ->
+    lists:foldl(fun ({_, N}, Acc) -> N + Acc end, 0, counters_for(Cid, State)).
+
+kinds_for(Cid, State) ->
+    [K || {K, _} <- counters_for(Cid, State)].
+
+endorsers_for(Cid, Kind, State) ->
+    case find_keyed(Cid, State) of
+        {ok, KindMap} ->
+            case find_keyed(Kind, KindMap) of
+                {ok, AM} -> [A || {A, _} <- AM];
+                _        -> []
+            end;
+        _ -> []
+    end.
+
+has_endorsed(Actor, Cid, Kind, State) ->
+    case find_keyed(Cid, State) of
+        {ok, KindMap} ->
+            case find_keyed(Kind, KindMap) of
+                {ok, AM} ->
+                    case find_keyed(Actor, AM) of
+                        {ok, N} -> N > 0;
+                        _       -> false
+                    end;
+                _ -> false
+            end;
+        _ -> false
+    end.
+
+%% ── Internal ──────────────────────────────────────────────────
+
+sum_counts([]) -> 0;
+sum_counts([{_, N} | Rest]) -> N + sum_counts(Rest).
+
+find_keyed(_, []) -> {error, not_found};
+find_keyed(K, [{K, V} | _]) -> {ok, V};
+find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).
+
+set_keyed(K, V, []) -> [{K, V}];
+set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)].