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/compose.sx

@@ -74,6 +74,19 @@
     (list (host/comp-render obj {}) (host/comp-render obj {"auth" "y"})))
   (list "guest" "member"))
 
+;; -- a THIRD domain over the SAME core: deps (collect transcluded refs). Proves step 8 —
+;; a new domain is just a dict + leaf, reusing seq/alt/each with no new control flow. --
+(host-cp-test "deps collects the refs a seq body transcludes (the contains DAG)"
+  (host/comp-deps (quote (seq (ref "c0") (text "x") (ref "c1"))) {})
+  (list "c0" "c1"))
+(host-cp-test "deps walks each — refs inside an iterated template are collected per item"
+  (host/comp-deps (quote (each (items {} {}) (ref "card"))) {})
+  (list "card" "card"))
+(host-cp-test "deps follows alt's taken branch (context-specific transclusions)"
+  (list (host/comp-deps (quote (alt (when (has "auth") (ref "member")) (else (ref "guest")))) {"auth" "y"})
+        (host/comp-deps (quote (alt (when (has "auth") (ref "member")) (else (ref "guest")))) {}))
+  (list (list "member") (list "guest")))
+
 (define host-cp-tests-run!
   (fn ()
     {:total (+ host-cp-pass host-cp-fail)