fed-sx-m2: Step 8f — live HTTP delivery dispatch (+ 10 tests)

Closes Step 8 (except 8b-timer which still gates on Blockers #3
send_after). New next/kernel/dispatch_http.erl wires the BIF
landed in Step 8e into a delivery_worker-shaped dispatch_fn.

dispatch_http API:
  make_dispatch_fn(PeerId, Cfg) -> fun((Activity) -> ok | {error,_})
  dispatch(Url, Activity, Cfg) -> ok | {error, _}
  inbox_url(BaseUrl, PeerAtom) -> <Base>/actors/<peer>/inbox
  resolve_peer_url(PeerId, Cfg) -> {ok, Base} | {error, no_peer_url}
  content_type/0 -> <<"application/vnd.fed-sx.activity">>

Peer URL resolution composes:
  {peer_url,    [{PeerId, BaseUrl}, ...]}   static map (tests)
  {peer_url_fn, fun ((PeerId) -> {ok, Url} | not_found)}  closure
                                            (Step 10c peer_actors)

Result mapping at dispatch/3:
  2xx           -> ok                    (worker drops the entry)
  non-2xx       -> {error, {status, N}}  (worker bumps attempt)
  resolver miss -> {error, no_peer_url}
  transport     -> {error, Reason}       (BIF re-raises, caught here)

httpc:request/4 BIF wrapper updated to catch host Eval_error via
SX `guard` and re-raise as Erlang `error:{network, ReasonBinary}`
so callers can handle it through standard try/catch — previously
the host exception bubbled past the Erlang try/catch surface
(which only handles er-thrown? / er-errored? / er-exited? markers).

Subtle Erlang-port note documented in dispatch/3: this port's
try/catch requires a literal class atom (`error:Reason`); the
generic `Class:Reason` syntax is not supported. dispatch_http
catches `error:Reason` only, which is what the BIF re-raise
produces.

Test: next/tests/dispatch_http.sh 10/10 against background
python3 http.server (always-200 handler):
  - module loads
  - inbox_url builds /actors/X/inbox
  - static :peer_url map resolves
  - missing peer -> {error, no_peer_url}
  - live POST -> 200 -> ok
  - closure path -> ok
  - closure on missing peer -> {error, no_peer_url}
  - closed port -> {error, _}
  - delivery_worker drains the queue via the live closure
  - :peer_url_fn closure path resolves

No-regression gates green: Erlang conformance 761/761,
httpc_request 10/10, http_listen_bif 5/5, delivery_worker 17/17,
delivery_retry 11/11, delivery_dispatch 7/7.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/erlang/runtime.sx

@@ -1607,8 +1607,8 @@
 ;;
 ;; Returns a 4-tuple {ok, StatusInt, HeadersProplist, BodyBinary}.
 ;; The native primitive raises Eval_error on DNS / connect / bad URL;
-;; that surfaces as an Erlang error marker the caller can catch via
-;; Erlang try/catch.
+;; we catch the host exception here and re-raise as an Erlang error
+;; marker so callers can use try/catch error:{network, _} -> _ end.
 (define
   er-bif-httpc-request
   (fn
@@ -1641,14 +1641,26 @@
              (er-binary? body) (list->string (map integer->char (get body :bytes)))
              (er-nil? body)    ""
              :else (raise (er-mk-error-marker (er-mk-atom "badarg"))))))
-        (let
-          ((resp (http-request method-str url-str headers-dict body-str)))
-          (er-mk-tuple
-            (list
-              (er-mk-atom "ok")
-              (get resp :status)
-              (er-of-sx-deep (get resp :headers))
-              (er-mk-binary (map char->integer (string->list (get resp :body)))))))))))
+        (let ((resp-ref (list nil)) (err-ref (list nil)))
+          (guard (c (:else (set-nth! err-ref 0 c)))
+            (set-nth! resp-ref 0
+              (http-request method-str url-str headers-dict body-str)))
+          (cond
+            (not (= (nth err-ref 0) nil))
+              ;; Host error -> Erlang error:{network, ReasonBinary}
+              (raise (er-mk-error-marker
+                (er-mk-tuple (list
+                  (er-mk-atom "network")
+                  (er-mk-binary (map char->integer
+                    (string->list (str (nth err-ref 0)))))))))
+            :else
+              (let ((resp (nth resp-ref 0)))
+                (er-mk-tuple
+                  (list
+                    (er-mk-atom "ok")
+                    (get resp :status)
+                    (er-of-sx-deep (get resp :headers))
+                    (er-mk-binary (map char->integer (string->list (get resp :body)))))))))))))
 
 ;; Register everything at load time.
 (define