host: polish — a third fold domain (deps) + a live execute-fold demo (/workflow-demo)

Two concrete demonstrations of the composition architecture:

THIRD DOMAIN (proves step 8's "a new domain is just a dict + leaf, no new control flow").
host/comp-deps folds a composition to the object ids it TRANSCLUDES — the static contains
DAG of a body. It reuses host/comp-fold's seq/alt/each dispatch verbatim; only the leaf
(collect `(ref ID)`) + accumulator (concat) are new. Useful in its own right (what a
(seq (ref c0) (each … (ref …))) body pulls in; context-specific — alt picks the taken
branch). compose suite 20/20.

LIVE EXECUTE-FOLD DEMO (makes step 7 tangible, parallel to /compose-demo for render).
/workflow-demo runs ONE composition object's :body through host/exec-run — the SAME structure
the render-fold would turn into HTML, folded by execute into a plan of effects (validate →
branch on status → notify each recipient). host/blog-seed-workflow-demo! + host/blog-workflow-
demo + route + serve.sh seed. Shows the behaviour model IS an execute-fold over a composition
object — the same object the block editor authors. blog suite 165/165.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/host/tests/blog.sx

@@ -856,6 +856,16 @@
       "application/x-www-form-urlencoded" "ctype=card-text&text=added+block"))
     (len (host/blog-body-refs "bdoc")))
   2)
+;; -- /workflow-demo: ONE composition object run through the EXECUTE-fold (step 7 live). The
+;; same :body structure the render-fold renders, folded to an effect log (status=ready ->
+;; validate, publish, notify each — not hold). --
+(host-bl-test "GET /workflow-demo runs the composition through the execute-fold"
+  (begin
+    (host/blog-seed-workflow-demo!)
+    (let ((html (dream-resp-body (host-bl-app (host-bl-req "/workflow-demo")))))
+      (list (contains? html "validate") (contains? html "publish")
+            (contains? html "notify") (contains? html "hold"))))
+  (list true true true false))
 (host-bl-test "a post with no schema'd type is vacuously valid"
   (host/blog-type-valid? "ppost" "(p \"anything\")") true)
 (host-bl-test "edit-submit rejects content violating the type schema (not saved)"