host P0.3: wire the seam into the live publish path (LIVE-VERIFIED)

Publishing a post now fires the on-publish behavior DAG through the seam. host/blog--{transport
(activity log), triggers (on-publish: create+article → publish-DAG), driver (records each effect in
the flow log), publish-engine (behavior/make-engine over the four adapters + the execute-fold runner
+ publish-ctx), fire-publish!, maybe-publish!}. Both write handlers (form-submit POST /new,
edit-submit POST /:slug/edit) detect the draft→published TRANSITION (fire-once) in the handler body
and run behavior/process. GET /flows renders the flow log (the effect-as-data the driver dispatched).

LIVE PROOF: logged in + POST /new on blog.rose-ash.com → /flows shows 'validate' + 'notify' (the
publish-DAG branched on the default urgent category), driven end-to-end by the real behavior engine.
Every piece is a seam adapter — swapping the runner for Erlang (RA) or the transport for fed-sx (TA)
federates this same wiring unchanged.

blog 207/207 (+4 P0.3), full host conformance 595/595. GAP: flow log is in-memory (P0.3b = persist).

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

lib/host/blog.sx

@@ -145,6 +145,43 @@
 (define host/blog--publish-ctx
   (fn (activity) (let ((o (get activity :object))) {"category" (get o :category) "slug" (get o :slug)})))
 
+;; ── P0.3: the seam WIRED on the live host ──────────────────────────────
+;; The publish ENGINE = the execute-fold runner (flows.sx) + a local-SX on-publish trigger registry
+;; + an in-process transport (the activity log = the event source) + the host driver (records each
+;; effect in the flow log). Publishing a post (draft→published, fire-once) builds the activity and
+;; runs it through behavior/process → the DAG's effects surface on /flows. In-memory logs for P0
+;; (durable-store backing is the follow-up). Every piece is a seam adapter — swap the runner for
+;; Erlang (RA) or the transport for fed-sx (TA) and this same wiring federates, unchanged.
+(define host/blog--activity-log (list))     ;; every publish activity emitted (the event source)
+(define host/blog--flow-log (list))         ;; what the flows DID (the driver's effect records)
+(define host/blog--transport
+  {:emit (fn (a) (set! host/blog--activity-log (concat host/blog--activity-log (list a))))
+   :deliver (fn () (list))})                ;; nothing inbound yet — P0 is synchronous
+(define host/blog--triggers
+  {:register! (fn (spec dag hint) nil)
+   :match (fn (a) (if (and (= (get a :type) "create") (= (get (get a :object) :type) "article"))
+                    (list {:dag host/blog--publish-dag}) (list)))})
+(define host/blog--driver
+  {:dispatch (fn (eff)
+               (begin (set! host/blog--flow-log
+                        (concat host/blog--flow-log
+                          (list {:verb (get eff :verb) :args (get eff :args)})))
+                      (list)))})            ;; record the effect; no follow-up activities (P0)
+(define host/blog--publish-engine
+  (behavior/make-engine {:triggers host/blog--triggers :runner host/flow--exec-runner
+                         :transport host/blog--transport :driver host/blog--driver
+                         :ctx-of host/blog--publish-ctx}))
+;; fire the publish flow for a slug: build the activity, run it through the seam. Returns the trace.
+(define host/blog--fire-publish!
+  (fn (slug)
+    (let ((a (host/blog--publish-activity slug)))
+      (if (nil? a) nil (behavior/process host/blog--publish-engine a)))))
+;; the draft→published TRANSITION (fire-once): only a non-published → published shift fires the flow.
+(define host/blog--maybe-publish!
+  (fn (slug prev-status new-status)
+    (if (and (not (= prev-status "published")) (= new-status "published"))
+      (host/blog--fire-publish! slug) nil)))
+
 ;; ── render ──────────────────────────────────────────────────────────
 ;; A post's sx_content is SX element markup -> HTML via render-page (which supplies
 ;; the server env so components resolve + keyword attrs are kept).
@@ -2376,9 +2413,12 @@
                             (p (a :href "/new" "Back")))))))
         (else
           (let ((slug (host/blog-slugify title)))
-            (begin
-              (host/blog-put! slug title (or sx-content "") status)
-              (dream-redirect (str "/" slug "/")))))))))
+            (let ((prev (host/blog-get slug)))
+              (begin
+                (host/blog-put! slug title (or sx-content "") status)
+                ;; P0.3: a draft→published transition fires the publish flow through the seam.
+                (host/blog--maybe-publish! slug (if prev (get prev :status) nil) status)
+                (dream-redirect (str "/" slug "/"))))))))))
 
 ;; The JSON CRUD /posts (create/update/delete) was DELETED in the greenfield
 ;; SX-native pivot (plans/relations-as-posts.md, "SX all the way out") — it was a
@@ -2593,6 +2633,8 @@
             (if (= (len issues) 0)
               (begin
                 (host/blog-put! slug title sx-content status)
+                ;; P0.3: a draft→published transition fires the publish flow through the seam.
+                (host/blog--maybe-publish! slug (get r :status) status)
                 ;; store the typed field values from the generic, type-driven form (Slice 8b)
                 (host/blog--set-field-values! slug
                   (reduce (fn (acc f)
@@ -2609,6 +2651,26 @@
                         (unquote (cons (quote ul) issue-items))
                         (p (a :href (unquote (str "/" slug "/edit")) "Back"))))))))))))))
 
+;; ── /flows — P0.3 acceptance surface ─────────────────────────────────
+;; What the publish workflows DID: each effect-as-data record the host driver dispatched, produced
+;; by running the on-publish DAG through the seam. Publishing a post appends here (live proof the
+;; behavior engine fired). Public read.
+(define host/blog-flows
+  (fn (req)
+    (host/blog--resp req 200
+      (host/blog--page req "Flows"
+        (quasiquote
+          (div (h1 "Flows")
+            (p "Effect-as-data from publish workflows — the seam: on-publish → publish-DAG → effects.")
+            (unquote
+              (if (= (len host/blog--flow-log) 0)
+                (quote (p (em "No flows yet — publish a post to fire the on-publish DAG.")))
+                (cons (quote ul)
+                  (map (fn (e)
+                         (quasiquote (li (strong (unquote (get e :verb))) " "
+                                       (unquote (if (> (len (get e :args)) 0) (str (first (get e :args))) "")))))
+                       host/blog--flow-log))))))))))
+
 ;; ── routes ──────────────────────────────────────────────────────────
 ;; Public reads + the create form. /, /posts, /new BEFORE /:slug (catch-all).
 ;; MUST be mounted LAST in the app so domain routes (/feed, /health) win.
@@ -2620,6 +2682,7 @@
     (dream-get "/tags" host/blog-tags-index)
     (dream-get "/meta" host/blog-meta-index)
     (dream-get "/workflow-demo" host/blog-workflow-demo)
+    (dream-get "/flows" host/blog-flows)
     (dream-get "/:slug/source" host/blog-source)
     (dream-get "/:slug/relate-options" host/blog-relate-options)
     (dream-get "/:slug" host/blog-post)))

lib/host/tests/blog.sx

@@ -1200,6 +1200,31 @@
   (list (host/flow--required-caps host/blog--publish-dag)
         (get (host/flow--bind host/flow--exec-runner host/blog--publish-dag) :ok))
   (list (list "effect" "branch") true))
+;; P0.3: the draft→published TRANSITION fires the publish flow THROUGH THE SEAM (engine = the
+;; execute-fold runner + on-publish registry + transport + host driver) → effects land in the flow log.
+(set! host/blog--flow-log (list))
+(set! host/blog--activity-log (list))
+(host-bl-test "P0.3: draft→published fires the publish flow through the seam → effects logged"
+  (begin
+    (host/blog-put! "p03a" "P" "(article (h1 \"x\"))" "published")
+    (host/blog--set-field-values! "p03a" {"category" "newsletter"})
+    (host/blog--maybe-publish! "p03a" "draft" "published")
+    (list (map (fn (e) (get e :verb)) host/blog--flow-log) (len host/blog--activity-log)))
+  (list (list "validate" "digest") 1))
+(host-bl-test "P0.3: published→published does NOT re-fire (fire-once on the transition)"
+  (begin
+    (host/blog--maybe-publish! "p03a" "published" "published")
+    (list (map (fn (e) (get e :verb)) host/blog--flow-log) (len host/blog--activity-log)))
+  (list (list "validate" "digest") 1))
+(host-bl-test "P0.3: a →draft transition does not fire"
+  (begin (host/blog--maybe-publish! "p03a" "published" "draft") (len host/blog--activity-log)) 1)
+(host-bl-test "P0.3: a fresh nil→published (new post) fires, urgent→notify"
+  (begin
+    (host/blog-put! "p03b" "U" "(article (h1 \"u\"))" "published")
+    (host/blog--set-field-values! "p03b" {"category" "urgent"})
+    (host/blog--maybe-publish! "p03b" nil "published")
+    (map (fn (e) (get e :verb)) host/blog--flow-log))
+  (list "validate" "digest" "validate" "notify"))
 
 (define
   host-bl-tests-run!