host P0.1: publish-activity contract for federated composition-flows

Business logic as federated composition-flows (plans/business-logic-fed-flows.md). P0.1: the
host describes a published post as a fed-sx activity — host/blog--publish-activity(slug) →
{:type "create" :actor "site" :id <CID> :object {:type "article" :slug :category}} — the
exact shape next/'s trigger machinery consumes (verified: next/tests/triggers_e2e.sh 10/10).
category (drives the flow branch: newsletter suspends / urgent fires / else skip) comes from
the "category" field-value, else the first tag, else "urgent". + host/blog--post-category.

Design decided: activity log = every CID delta (event source); triggers = declared subscriptions
(DefineTrigger); flows hybrid (SX composition for simple via the execute-fold, named Erlang flows
for complex); federated execution = Erlang (next/); the type carries content+relations+behavior.

blog 200/200 (+3: contract, category fallback, missing-post nil).

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

lib/host/blog.sx

@@ -107,6 +107,28 @@
       (fn (acc slug) (if acc acc (if (= (host/blog-cid slug) cid) slug acc)))
       nil (host/blog-slugs))))
 
+;; ── business logic as federated composition-flows (plans/business-logic-fed-flows.md) ──
+;; P0.1: the PUBLISH-ACTIVITY contract. A published post is described as a fed-sx activity —
+;; the same shape next/'s trigger machinery consumes ({:type verb :actor :id CID :object …}).
+;; The trigger (on-publish → a flow, e.g. blog_publish_digest) fires on a matching activity.
+;; category (drives the flow's branch: newsletter suspends, urgent fires now, else skip) comes
+;; from the post's "category" field-value, else its first tag, else "urgent" (fires the demo).
+(define host/blog--post-category
+  (fn (slug)
+    (let ((fc (get (host/blog-field-values-of slug) "category")))
+      (if (and fc (not (= fc ""))) fc
+        (let ((tags (host/blog-out slug "tagged")))
+          (if (> (len tags) 0) (first tags) "urgent"))))))
+(define host/blog--publish-activity
+  (fn (slug)
+    (let ((r (host/blog-get slug)))
+      (if (nil? r) nil
+        {:type "create"                               ;; publishing = the article enters the fed world
+         :actor "site"                                ;; P0: a fixed site actor; per-author later
+         :id (host/blog-cid slug)                     ;; the object's content CID
+         :object {:type "article" :slug slug
+                  :category (host/blog--post-category slug)}}))))
+
 ;; ── 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).

lib/host/tests/blog.sx

@@ -1160,6 +1160,29 @@
 (host-bl-test "by-cid of an unknown CID is nil"
   (host/blog-by-cid "znope-nope") nil)
 
+;; ── P0.1: business-logic fed-flows — the publish-activity contract ──
+;; a published post is described as a fed-sx create activity that next/'s trigger machinery
+;; consumes; category (drives the flow branch) comes from a field-value, else a tag, else urgent.
+(host-bl-test "publish-activity describes a published post as a fed-sx create activity"
+  (begin
+    (host/blog-put! "pub1" "Pub One" "(article (h1 \"P\"))" "published")
+    (host/blog--set-field-values! "pub1" {"category" "newsletter"})
+    (let ((a (host/blog--publish-activity "pub1")))
+      (list (get a :type) (get (get a :object) :type) (get (get a :object) :category)
+            (get (get a :object) :slug) (not (nil? (get a :id))))))
+  (list "create" "article" "newsletter" "pub1" true))
+(host-bl-test "publish-activity category falls back to a tag, else urgent"
+  (begin
+    (host/blog-put! "pub2" "Pub Two" "(article (h1 \"Q\"))" "published")
+    (host/blog-seed! "urgent" "Urgent" "(article (h1 \"u\"))" "published")
+    (host/blog-relate! "pub2" "urgent" "tagged")
+    (host/blog-put! "pub3" "Pub Three" "(article (h1 \"R\"))" "published")   ;; no field, no tag
+    (list (get (get (host/blog--publish-activity "pub2") :object) :category)
+          (get (get (host/blog--publish-activity "pub3") :object) :category)))
+  (list "urgent" "urgent"))
+(host-bl-test "publish-activity of a missing post is nil"
+  (host/blog--publish-activity "nope-nope-nope") nil)
+
 (define
   host-bl-tests-run!
   (fn ()

plans/business-logic-fed-flows.md

@@ -0,0 +1,65 @@
+# Business logic as federated composition-flows
+
+**Vision:** business logic is part of an object's composition — declared on its **type**,
+alongside content grammar + allowed relations. State changes federate over fed-sx; federated
+services execute the business logic as durable **flows**.
+
+**Design (decided 2026-07-02):**
+- **Activity log = every CID delta** — the federated event source of truth. Any content change
+  (new CID, per host/blog--cid-of: content in the record → CID; relations are external → not).
+- **Triggers = declared subscriptions** — a type declares named triggers (on-publish, on-relate,
+  …); flows fire only on matching ones. (fed-sx `DefineTrigger`: activity-type → flow-name + guard
+  + actor-scope.) Log complete, execution precise.
+- **Flows = hybrid** — simple logic authored as **SX composition** (the execute-fold: effect/alt/
+  each — already live in /workflow-demo); an escape hatch to named **Erlang flows**
+  (next/flow/*.erl, effect-as-data, deterministic replay, suspend/resume) for the complex.
+- **Federated execution = Erlang** (`next/` fed-sx Milestone-1 kernel: trigger_registry +
+  flow_dispatch + pipeline post-append fan-out). Authoring stays SX; the fed-sx activity is the
+  bridge. flow-on-sx (Scheme, lib/flow) remains for purely-local durable logic.
+- **The type carries its whole contract:** fields+grammar (content) · allowed relations
+  (external) · triggers+flows (behavior). All composition, all editable in the type-def editor.
+
+**Verified baseline:** `next/tests/triggers_e2e.sh` = 10/10 — publish activity → trigger →
+blog_publish_digest flow (urgent/newsletter-suspend/draft-skip/guard-reject/dedup). This is the
+reference P0 wires the live host onto.
+
+## P0 — publish workflow, end-to-end (spike)
+Prove: live host publishes a post → fed-sx activity → on-publish trigger → blog_publish_digest.
+
+- [x] **P0.1 — the publish-activity contract (SX side).** host/blog--publish-activity(slug):
+  a post record → the fed-sx activity {:type "create" :actor "site" :id <CID> :object {:type
+  "article" :category … :slug …}}. category from field-value "category", else first tag, else
+  "urgent". + host/blog--post-category. blog 200/200 (3 tests). DONE 2026-07-02.
+- [ ] **P0.2 — the dispatch bridge.** On publish (host/blog-edit-submit status→published, or a
+  dedicated publish action), emit the activity into the trigger machinery. RUNTIME CHOICE for P0:
+  in-process — serve.sh loads next/ kernel + registers the on-publish trigger; host emits via the
+  erlang-on-sx bridge (erlang-eval-ast pipeline:apply_triggers). (P3 replaces this with real fed-sx
+  delivery over next/kernel/http_server.erl.)
+- [ ] **P0.3 — the effect is visible.** The flow's digest_sent effect surfaces (a durable record /
+  a DigestSent activity back in the log / shown on the post or a /flows page). Close the local loop.
+
+## P1 — types declare behavior (generalize)
+- [ ] A Composition field / the type carries a :triggers list (on-publish → flow-name + guard) —
+  edited in the type-def editor, like grammar + relations.
+- [ ] A fold turns a type's declared behavior into DefineTrigger + flow registrations at boot.
+- [ ] Simple flows authored as SX composition (execute-fold) → compiled/dispatched to the engine;
+  complex ones reference named Erlang flows.
+
+## P2 — state-change → activity emission (the CID-delta event source)
+- [ ] Every content mutation (new CID) appends a state-change activity to the log. Define the
+  activity envelope (verb, actor, object CID, prev CID, delta summary).
+- [ ] Wire the host's write path (put!/set-comp!/edit-submit) to the append.
+
+## P3 — federation proper
+- [ ] Activities cross peers via next/ delivery (http_server / outbox / follower_graph). A remote
+  service's trigger_registry fires the flow. Everything works over fed-sx.
+
+## P4 — close the loop
+- [ ] Flow effects mutate objects back durably (a flow's DescribeEffects → host writes / new
+  activities), so business logic can change state, which federates, which triggers more flows.
+
+## Progress log (newest first)
+- 2026-07-02 — P0.1 done. host/blog--publish-activity + host/blog--post-category; the publish
+  contract in SX, 200/200. Verified next/ triggers e2e baseline 10/10. Roadmap anchored. NEXT:
+  P0.2 the dispatch bridge (in-process: serve.sh loads next/ kernel + registers the on-publish
+  trigger; host emits the activity via the erlang-on-sx bridge to pipeline:apply_triggers).