fed-sx-m2: Step 7c — outbox delivery_set integration + 4 tests

outbox:publish/2 now computes the audience-resolved delivery set
after sign + log and stashes it in the Result proplist as
{delivery_set, [ActorId, ...]}. Step 8's delivery-queue worker
reads it off the publish result.

New compute_delivery_set/3(Request, Signed, Context):
  - Pulls :follower_graph from Context (defaults to empty graph)
  - Calls recipients_envelope/2 to synthesise a minimal envelope
    from Request's :to / :cc + Signed's :actor
  - Routes through delivery:delivery_set/3 unchanged

The envelope construct/4 surface doesn't carry :to / :cc (only
type / actor / published / object), and changing that ripples
through every envelope shape test. recipients_envelope/2 keeps
the compute boundary local to outbox.

4 new cases in outbox_publish.sh (17/17 total):
  - Result :delivery_set empty default
  - explicit :to -> [bob] in set
  - followers symbol expands via Context :follower_graph
  - self-suppression (alice in :to drops to []bob])

Module loads rebumped: follower_graph + delivery added as
dependencies; outbox shifts from epoch 5 to epoch 7. Internal
sx_server timeout bumped 240s -> 480s to fit the larger module
set.

Step 7 fully closed (7a delivery module + 7b public expansion
+ 7c outbox integration). Federation now has the end-to-end
audience resolution: an outbound activity's :to / :cc plus any
follower_graph expansion becomes a deduped recipient list ready
for Step 8 to dispatch.

Conformance running + adjacent gate running.

next/tests/outbox_publish.sh

@@ -45,6 +45,10 @@ cat > "$TMPFILE" <<EPOCHS
 (epoch 4)
 (eval "(get (erlang-load-module (file-read \"next/kernel/pipeline.erl\")) :name)")
 (epoch 5)
+(eval "(get (erlang-load-module (file-read \"next/kernel/follower_graph.erl\")) :name)")
+(epoch 6)
+(eval "(get (erlang-load-module (file-read \"next/kernel/delivery.erl\")) :name)")
+(epoch 7)
 (eval "(get (erlang-load-module (file-read \"next/kernel/outbox.erl\")) :name)")
 
 ;; Happy path: publish returns {ok, Result, NewLog}, log tip advances
@@ -82,9 +86,25 @@ cat > "$TMPFILE" <<EPOCHS
 ;; CID stable: same Request twice (across fresh logs) -> same CID
 (epoch 18)
 (eval "(get (erlang-eval-ast \"${PRELUDE} {ok, R1, _} = outbox:publish(Req, Ctx), {ok, L0b} = log:open(alice, base), Ctx_b = [{actor_id,alice},{published,100},{key_spec,KS},{actor_state,AS},{log,L0b}], {ok, R2, _} = outbox:publish(Req, Ctx_b), {ok, C1} = envelope:get_field(cid, R1), {ok, C2} = envelope:get_field(cid, R2), C1 =:= C2\") :name)")
+
+;; Step 7c: Result has :delivery_set, empty when no :to/:cc + no graph
+(epoch 20)
+(eval "(get (erlang-eval-ast \"${PRELUDE} {ok, R, _} = outbox:publish(Req, Ctx), envelope:get_field(delivery_set, R) =:= {ok, []}\") :name)")
+
+;; Step 7c: explicit :to -> delivery_set carries the recipient
+(epoch 21)
+(eval "(get (erlang-eval-ast \"${PRELUDE} ReqTo = [{type, note}, {object, [{content, hi}]}, {to, bob}], {ok, R, _} = outbox:publish(ReqTo, Ctx), envelope:get_field(delivery_set, R) =:= {ok, [bob]}\") :name)")
+
+;; Step 7c: followers symbol expands via graph in Context
+(epoch 22)
+(eval "(get (erlang-eval-ast \"${PRELUDE} F = [{actor, bob}, {type, follow}, {object, alice}], A = [{actor, alice}, {type, accept}, {object, F}], Graph = follower_graph:fold(A, follower_graph:fold(F, follower_graph:new())), CtxG = Ctx ++ [{follower_graph, Graph}], ReqFol = [{type, note}, {object, [{content, hi}]}, {to, followers}], {ok, R, _} = outbox:publish(ReqFol, CtxG), envelope:get_field(delivery_set, R) =:= {ok, [bob]}\") :name)")
+
+;; Step 7c: self-suppression — alice's :to including alice drops it
+(epoch 23)
+(eval "(get (erlang-eval-ast \"${PRELUDE} ReqSelf = [{type, note}, {object, [{content, hi}]}, {to, [alice, bob]}], {ok, R, _} = outbox:publish(ReqSelf, Ctx), envelope:get_field(delivery_set, R) =:= {ok, [bob]}\") :name)")
 EPOCHS
 
-OUTPUT=$(timeout 240 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
+OUTPUT=$(timeout 480 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
 
 check() {
   local epoch="$1" desc="$2" expected="$3"
@@ -108,11 +128,15 @@ check() {
 check  2  "envelope module loaded"             "envelope"
 check  3  "log module loaded"                  "log"
 check  4  "pipeline module loaded"             "pipeline"
-check  5  "outbox module loaded"               "outbox"
+check  7  "outbox module loaded"               "outbox"
 check 10  "happy path tip advances to 1"       "true"
 check 11  "result :cid matches activity"       "true"
 check 12  "signed activity in log entries"     "true"
 check 13  "duplicate publish -> replay"        "ok"
+check 20  "Result :delivery_set empty default" "true"
+check 21  "explicit :to -> [bob] in set"       "true"
+check 22  "followers symbol expands via graph" "true"
+check 23  "self-suppression on alice in :to"   "true"
 check 14  "replay leaves log tip at 1"         "true"
 check 15  "bad key material -> bad_signature"  "ok"
 check 16  "distinct timestamps -> tip 2"       "true"