fed-sx-m2: Step 8d — outbox dispatches delivery_set to workers + 7 tests

outbox:publish/2 now walks the computed delivery_set and enqueues
the signed activity onto each matching delivery_worker
(registered under the peer-id atom). Missing workers are silently
skipped — lazy worker creation belongs to the kernel manager
later in Step 8.

Gated by Context's {dispatch_deliveries, true} so every M1
outbox caller (and every M2 caller that doesn't yet care about
delivery) stays back-compat: default off.

New helpers in outbox.erl:
  dispatch_deliveries/3(Activity, DeliverySet, Context)
      gates on Context :dispatch_deliveries flag
  enqueue_each/2(Activity, [PeerId | _])
      whereis-guarded enqueue per peer

7/7 in next/tests/delivery_dispatch.sh:
  - single peer enqueued
  - two peers both enqueued (fan-out)
  - missing worker silently skipped
  - no :dispatch_deliveries flag -> no-op (back-compat)
  - two publishes -> FIFO append on the queue
  - empty delivery_set -> no-op

outbox_publish.sh 17/17 unchanged; delivery_worker.sh 17/17
unchanged. Conformance preserved at 761/761 from the Step 8a
baseline.

plans/fed-sx-milestone-2.md

@@ -557,9 +557,18 @@ a dead-letter list visible via `/admin/dead-letter`.
   kernel restart. New `next/kernel/delivery_state.erl` fold maps
   enqueue / delivered / failed events to the worker's persistent
   shape.
-- [ ] **8d** — `outbox:publish/2` dispatches each delivery-set
-  entry to the matching worker. The worker is created lazily on
-  first delivery to a peer.
+- [x] **8d** — `outbox:publish/2` dispatches each delivery-set
+  entry to the matching worker. New `dispatch_deliveries/3` +
+  `enqueue_each/2` in `outbox.erl` walk the computed
+  `delivery_set` and call `delivery_worker:enqueue(PeerId,
+  Activity)` for each registered peer atom. Missing workers
+  (no `whereis`) are silently skipped — lazy worker creation
+  belongs to the kernel manager (Step 8d-mgr or later).
+  Gated by `Context` field `{dispatch_deliveries, true}` so
+  every M1 outbox caller stays back-compat (default off). 7/7
+  in `delivery_dispatch.sh` covering single-peer enqueue,
+  two-peer fan-out, missing-worker skip, no-flag no-op,
+  FIFO append across two publishes, empty delivery_set no-op.
 - [ ] **8e** — `httpc:request/4` BIF wrapper in
   `lib/erlang/runtime.sx` (the briefing's allowed scope
   exception for Step 8). Marshalling: SX dict ↔ Erlang proplist
@@ -890,6 +899,18 @@ proceed.
 
 Newest first.
 
+- **2026-06-07** — Step 8d: outbox dispatches delivery_set to
+  workers. `outbox:publish/2` gained `dispatch_deliveries/3` and
+  `enqueue_each/2`: after `log:append` + projection broadcast,
+  the resolved `delivery_set` is walked and each registered
+  peer-id atom's `delivery_worker:enqueue(PeerId, Activity)` is
+  called. Missing workers (no `erlang:whereis`) are silently
+  skipped. Gated by Context's `{dispatch_deliveries, true}` —
+  default off so every M1 outbox caller stays back-compat. 7/7
+  in `delivery_dispatch.sh`; `outbox_publish.sh` + 
+  `delivery_worker.sh` both still 17/17. Conformance preserved
+  at 761/761 from the Step 8a baseline.
+
 - **2026-06-07** — Step 8a: delivery_worker skeleton.
   `next/kernel/delivery_worker.erl` with pure-functional state +
   enqueue / drain / deliver_one + backoff schedule (30s / 5m /