host: the adapter seam for business-logic-as-composition (design-first)

lib/host/behavior.sx — the substrate-independent seam every runner/transport/registry/driver
plugs into. An engine bundles four dict-of-functions adapters (trigger-registry, runner,
transport, driver); behavior/process folds an ACTIVITY through the pipeline: emit → match
triggers → run each behavior DAG → dispatch each effect-as-data → recurse on new activities
(loop closure, depth-guarded at 8). Every stage injected, so the same DAG + engine run over the
synchronous op-table runner / Erlang durable / celery-sx / fed-sx transport unchanged.

Reference tests (mock adapters) prove the contract: publish→trigger→runner→effect flows; a
non-matching activity fires nothing (log complete, execution precise); an effect that emits a new
activity re-triggers (loop closes); an unbounded loop is depth-guarded (terminates). Wired into
conformance.sh + serve.sh MODULES. behavior 4/4; full host conformance 575/575.

Next: P0 supplies the REAL adapters (publish activity ← host/blog--publish-activity, local-SX
trigger, sync op-table runner over a publish-DAG, host driver) — same engine.

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

lib/host/conformance.sh

@@ -94,6 +94,7 @@ MODULES=(
   "lib/host/relations.sx"
   "lib/host/compose.sx"
   "lib/host/execute.sx"
+  "lib/host/behavior.sx"
   "lib/host/htmlsx.sx"
   "lib/host/blog.sx"
   "lib/host/page.sx"
@@ -112,6 +113,7 @@ SUITES=(
   "relations   host-rl-tests-run!  lib/host/tests/relations.sx"
   "blog        host-bl-tests-run!  lib/host/tests/blog.sx"
   "htmlsx      host-ht-tests-run!  lib/host/tests/htmlsx.sx"
+  "behavior    host-be-tests-run!  lib/host/tests/behavior.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"