diff --git a/lib/host/conformance.sh b/lib/host/conformance.sh
index e7efc1d2..e3270964 100755
--- a/lib/host/conformance.sh
+++ b/lib/host/conformance.sh
@@ -97,6 +97,7 @@ MODULES=(
   "lib/host/behavior.sx"
   "lib/host/flows.sx"
   "lib/host/ra.sx"
+  "lib/host/ta.sx"
   "lib/host/htmlsx.sx"
   "lib/host/blog.sx"
   "lib/host/page.sx"
@@ -118,6 +119,7 @@ SUITES=(
   "behavior    host-be-tests-run!  lib/host/tests/behavior.sx"
   "flows       host-fl-tests-run!  lib/host/tests/flows.sx"
   "ra          host-ra-tests-run!  lib/host/tests/ra.sx"
+  "ta          host-ta-tests-run!  lib/host/tests/ta.sx"
   "compose     host-cp-tests-run!  lib/host/tests/compose.sx"
   "execute     host-ex-tests-run!  lib/host/tests/execute.sx"
   "session     host-se-tests-run!  lib/host/tests/session.sx"
diff --git a/lib/host/serve.sh b/lib/host/serve.sh
index f575c063..0b566198 100755
--- a/lib/host/serve.sh
+++ b/lib/host/serve.sh
@@ -112,6 +112,7 @@ MODULES=(
   "lib/host/behavior.sx"
   "lib/host/flows.sx"
   "lib/host/ra.sx"
+  "lib/host/ta.sx"
   "lib/host/htmlsx.sx"
   "lib/host/blog.sx"
   "lib/host/server.sx"
diff --git a/lib/host/ta.sx b/lib/host/ta.sx
new file mode 100644
index 00000000..1689e688
--- /dev/null
+++ b/lib/host/ta.sx
@@ -0,0 +1,41 @@
+;; lib/host/ta.sx — TA: the fed-sx TRANSPORT ADAPTER (plans/business-logic-fed-flows.md). A seam
+;; transport {:emit :deliver} (behavior.sx) over a directional WIRE, so an activity emitted on one
+;; instance reaches another instance's engine and fires ITS behaviors — federation.
+;;
+;; The transport is the SERIALIZATION boundary: activities cross the wire as SX-source strings
+;; (string-keyed for persist/wire safety, reconstructed on arrival). The wire is dumb string
+;; transport {:send :recv}; the REAL wire is next/ delivery (outbox→peers / inbox), DEFERRED to
+;; TA-live (same persistent-kernel prerequisite as RA-live); a mem-wire drives the tests.
+;;
+;; DIRECTIONAL: :emit → an OUT wire (this instance's outbox → followers); :deliver → an IN wire
+;; (its inbox ← those it follows). Separate channels, so processing a delivered activity (which the
+;; seam re-emits to log it) goes to THIS instance's outbox, NOT back into the inbox — no loop.
+
+;; canonical activity (keyword-keyed) <-> the flat string-keyed WIRE form (persist/serialise-safe).
+(define host/ta--activity->wire
+  (fn (a)
+    {"verb" (get a :verb) "actor" (get a :actor) "object" (get a :object)
+     "type" (get a :object-type) "slug" (get a :slug) "category" (get a :category)
+     "relation" (get a :relation) "target" (get a :target)
+     "delta" (get a :delta) "id" (get a :id)}))
+(define host/ta--wire->activity
+  (fn (w)
+    {:verb (get w "verb") :actor (get w "actor") :object (get w "object")
+     :object-type (get w "type") :slug (get w "slug") :category (get w "category")
+     :relation (get w "relation") :target (get w "target")
+     :delta (get w "delta") :id (get w "id")}))
+(define host/ta--serialize   (fn (a) (serialize (host/ta--activity->wire a))))
+(define host/ta--deserialize (fn (s) (host/ta--wire->activity (parse-safe s))))
+
+;; the transport: emit serialises to the OUT wire; deliver deserialises from the IN wire.
+(define host/ta--make-transport
+  (fn (out-wire in-wire)
+    {:emit (fn (a) ((get out-wire :send) (host/ta--serialize a)))
+     :deliver (fn () (map host/ta--deserialize ((get in-wire :recv))))}))
+
+;; an in-memory directional wire {:send :recv} (a captured mutable queue) — the test substrate.
+(define host/ta--make-mem-wire
+  (fn ()
+    (let ((q (list)))
+      {:send (fn (s) (set! q (concat q (list s))))
+       :recv (fn () (let ((batch q)) (begin (set! q (list)) batch)))})))
diff --git a/lib/host/tests/ta.sx b/lib/host/tests/ta.sx
new file mode 100644
index 00000000..8db7a1ae
--- /dev/null
+++ b/lib/host/tests/ta.sx
@@ -0,0 +1,68 @@
+;; lib/host/tests/ta.sx — TA the fed-sx transport adapter (lib/host/ta.sx). Proves the federation
+;; loop with an in-memory wire: an activity emitted on instance A crosses to instance B and fires
+;; B's engine. The REAL wire (next/ delivery) is TA-live (deferred, persistent-kernel prerequisite).
+
+(define host-ta-pass 0)
+(define host-ta-fail 0)
+(define host-ta-fails (list))
+(define host-ta-test
+  (fn (name actual expected)
+    (if (= actual expected)
+      (set! host-ta-pass (+ host-ta-pass 1))
+      (begin (set! host-ta-fail (+ host-ta-fail 1))
+        (append! host-ta-fails {:name name :actual actual :expected expected})))))
+
+;; ── serialization: activities cross the wire as SX-source and round-trip ──
+(host-ta-test "a content activity round-trips through the wire (serialize → deserialize)"
+  (let ((r (host/ta--deserialize (host/ta--serialize
+             {:verb "create" :actor "alice" :object "cid1" :object-type "article"
+              :slug "post1" :category "urgent" :delta "create" :id "create:cid1"}))))
+    (list (get r :verb) (get r :object-type) (get r :slug) (get r :category) (get r :id)))
+  (list "create" "article" "post1" "urgent" "create:cid1"))
+(host-ta-test "a relation activity round-trips (relation + target preserved)"
+  (let ((r (host/ta--deserialize (host/ta--serialize
+             {:verb "add" :actor "site" :object "p1" :object-type "article"
+              :relation "tagged" :target "urgent" :delta "add tagged urgent" :id "add:p1:tagged:urgent"}))))
+    (list (get r :verb) (get r :relation) (get r :target) (get r :id)))
+  (list "add" "tagged" "urgent" "add:p1:tagged:urgent"))
+
+;; ── the in-memory wire accumulates + drains ──
+(host-ta-test "mem-wire: send accumulates, recv drains"
+  (let ((w (host/ta--make-mem-wire)))
+    (begin ((get w :send) "a") ((get w :send) "b")
+      (let ((batch ((get w :recv)))) (list (len batch) (len ((get w :recv)))))))
+  (list 2 0))
+
+;; ── the federation LOOP: A emits → wire → B pump → B's behavior fires on A's activity ──
+(define ta-wire-ab (host/ta--make-mem-wire))       ;; A's outbox → B's inbox
+(define ta-sink    (host/ta--make-mem-wire))       ;; B's outbox (its own followers; ignored here)
+(define ta-empty   (host/ta--make-mem-wire))       ;; A's inbox (empty)
+(define ta-A (host/ta--make-transport ta-wire-ab ta-empty))
+(define ta-fired (list))
+(define ta-B-engine
+  (behavior/make-engine
+    {:triggers {:register! (fn (s d h) nil)
+                :match (fn (a) (if (= (get a :verb) "create") (list {:dag "peer-dag"}) (list)))}
+     :runner {:capabilities (list)
+              :run (fn (dag env) {:status "done"
+                                  :effects (list {:kind "peer-fired" :for (get (get env :activity) :id)})})}
+     :transport (host/ta--make-transport ta-sink ta-wire-ab)   ;; B delivers from wire-ab, emits to sink
+     :driver {:dispatch (fn (eff) (begin (set! ta-fired (concat ta-fired (list eff))) (list)))}}))
+(host-ta-test "federation loop: A emits → wire → B pump → B's behavior fires on A's activity"
+  (begin
+    (set! ta-fired (list))
+    ((get ta-A :emit) {:verb "create" :actor "alice" :object "cid1" :object-type "article" :id "create:cid1"})
+    (let ((trace (behavior/pump ta-B-engine)))
+      (list (len (get trace :emitted)) (get (first ta-fired) :kind) (get (first ta-fired) :for))))
+  (list 1 "peer-fired" "create:cid1"))
+(host-ta-test "directional: B re-emits to its OWN outbox, not back into the inbox (no loop)"
+  (begin
+    ((get ta-A :emit) {:verb "create" :actor "a" :object "c2" :object-type "article" :id "create:c2"})
+    (behavior/pump ta-B-engine)                                  ;; delivers + fires; re-emit → sink
+    (len (get (behavior/pump ta-B-engine) :emitted)))            ;; wire-ab now empty → nothing
+  0)
+
+(define host-ta-tests-run!
+  (fn ()
+    {:total (+ host-ta-pass host-ta-fail)
+     :passed host-ta-pass :failed host-ta-fail :fails host-ta-fails}))
diff --git a/plans/business-logic-fed-flows.md b/plans/business-logic-fed-flows.md
index 6ef191b0..1d79d22a 100644
--- a/plans/business-logic-fed-flows.md
+++ b/plans/business-logic-fed-flows.md
@@ -271,10 +271,23 @@ the flow instance Id is the resume handle.
   The runner + marshalling + suspend/resume mechanics are all proven; this is process lifecycle + wiring.
 
 ## TA — the FED-SX TRANSPORT adapter   ← federation proper
-- [ ] A seam transport over next/ delivery: :emit → outbox → peers; :deliver → inbox. A remote
-  peer's engine fires its own triggers. Everything works over fed-sx. RISK: next/ delivery M2
-  blockers (er-scheduler context). Needs the ACTOR MODEL real (:actor was a P0 placeholder —
-  peer_actors / follower_graph / per-author identity).
+- [x] **TA TRANSPORT BUILT + the federation LOOP PROVEN 2026-07-02.** lib/host/ta.sx — a seam
+  transport {:emit :deliver} over a DIRECTIONAL wire (out=outbox→followers, in=inbox←follows). The
+  transport is the SERIALIZATION boundary: activities cross as SX-source strings via host/ta--
+  serialize/deserialize (keyword-keyed activity ↔ flat string-keyed wire form — the P2 activity
+  fields). host/ta--make-transport(out-wire, in-wire) + host/ta--make-mem-wire (an in-memory
+  directional queue). PROVEN (ta 5/5): a content + a relation activity round-trip through the wire;
+  the FEDERATION LOOP — instance A emits an activity → the wire carries it → instance B's
+  behavior/pump delivers + processes it → B's engine fires ITS behavior on A's activity; DIRECTIONAL
+  (B re-emits to its own outbox, not back into the inbox — no loop). This is "everything works over
+  fed-sx" proven at the seam. Full host conformance green.
+- [ ] **TA-LIVE (deferred — same shape as RA-live).** Swap the mem-wire for the REAL next/ delivery
+  wire (outbox → http_server → peer inbox). Needs: (a) a PERSISTENT next/ kernel process (gen_servers
+  don't survive across erlang-eval-ast calls — the RA-live finding; next/ outbox/http_server are the
+  persistent side); (b) the ACTOR MODEL real (:actor is a "site" placeholder — peer_actors /
+  follower_graph / per-author identity decide WHO the out-wire delivers to); (c) push /activities
+  (the P2 event source) onto the out-wire. RISK: next/ delivery M2 blockers (er-scheduler context).
+  The transport contract + serialization + the loop are proven; TA-live is the wire impl + placement.
 
 ## AX — artdag GROWS control-flow (business logic MIGRATES to artdag) [DEMAND-DRIVEN]
 Today artdag is pure dataflow and the execute-fold is the synchronous control-flow runner. That's
@@ -303,6 +316,13 @@ covers everything until a DAG's cost/latency/placement forces the substrate.
   activities), so business logic can change state, which federates, which triggers more flows.
 
 ## Progress log (newest first)
+- 2026-07-02 — TA TRANSPORT built + the federation LOOP proven (lib/host/ta.sx, ta 5/5). A seam
+  transport over a directional wire (serialization boundary; activities cross as SX-source). Proven
+  in-memory: A emits → wire → B pump → B's engine fires ITS behavior on A's activity (directional, no
+  loop). "Everything works over fed-sx" proven at the seam. TA-live (real next/ delivery wire) deferred
+  — needs the persistent kernel (RA-live finding) + the actor model (who to deliver to). NEXT: the
+  DISTRIBUTED HALF is now all proven-at-the-seam (RA + TA); the remaining live steps (RA-live, TA-live)
+  share ONE prerequisite — a persistent next/ kernel process + the actor model. Or P4/AX/RX.
 - 2026-07-02 — P2 DONE + LIVE-VERIFIED. All observable state changes now emit canonical activities
   through the seam: content Create/Update + relation Add/Remove. DEBT #1 fixed (per-event ids; edge-
   based for relations). The activity log is the durable event source, surfaced at /activities. Live: