Restructure boundary specs: move app-specific I/O out of language contract

boundary.sx now contains only generic web-platform I/O primitives that
any SX host would provide (current-user, request-arg, url-for, etc.).

Moved to boundary-app.sx (deployment-specific):
- Inter-service: frag, query, action, service
- Framework: htmx-request?, g, jinja-global
- Domain: nav-tree, get-children, relations-from

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/boundary-app.sx

@@ -1,9 +1,12 @@
 ;; ==========================================================================
 ;; boundary-app.sx — Deployment-specific boundary declarations
 ;;
-;; Layout context I/O primitives for THIS deployment's service architecture.
+;; I/O primitives specific to THIS deployment's architecture:
+;; inter-service communication, framework bindings, domain concepts,
+;; and layout context providers.
+;;
 ;; These are NOT part of the SX language contract — a different deployment
-;; would declare different layout contexts here.
+;; would declare different primitives here.
 ;;
 ;; The core SX I/O contract lives in boundary.sx.
 ;; Per-service page helpers live in {service}/sx/boundary.sx.
@@ -11,7 +14,92 @@
 
 
 ;; --------------------------------------------------------------------------
-;; Layout context providers — deployment-specific I/O
+;; Inter-service communication — microservice architecture
+;; --------------------------------------------------------------------------
+
+(define-io-primitive "frag"
+  :params (service frag-type &key)
+  :returns "string"
+  :async true
+  :doc "Fetch cross-service HTML fragment."
+  :context :request)
+
+(define-io-primitive "query"
+  :params (service query-name &key)
+  :returns "any"
+  :async true
+  :doc "Fetch data from another service via internal HTTP."
+  :context :request)
+
+(define-io-primitive "action"
+  :params (service action-name &key)
+  :returns "any"
+  :async true
+  :doc "Call an action on another service via internal HTTP."
+  :context :request)
+
+(define-io-primitive "service"
+  :params (service-or-method &rest args &key)
+  :returns "any"
+  :async true
+  :doc "Call a domain service method. Two-arg: (service svc method). One-arg: (service method) uses bound handler service."
+  :context :request)
+
+
+;; --------------------------------------------------------------------------
+;; Framework bindings — Quart/Jinja2/HTMX specifics
+;; --------------------------------------------------------------------------
+
+(define-io-primitive "htmx-request?"
+  :params ()
+  :returns "boolean"
+  :async true
+  :doc "True if current request has HX-Request header."
+  :context :request)
+
+(define-io-primitive "g"
+  :params (key)
+  :returns "any"
+  :async true
+  :doc "Read a value from the Quart request-local g object."
+  :context :request)
+
+(define-io-primitive "jinja-global"
+  :params (key &rest default)
+  :returns "any"
+  :async false
+  :doc "Read a Jinja environment global."
+  :context :request)
+
+
+;; --------------------------------------------------------------------------
+;; Domain concepts — navigation, relations
+;; --------------------------------------------------------------------------
+
+(define-io-primitive "nav-tree"
+  :params ()
+  :returns "list"
+  :async true
+  :doc "Navigation tree as list of node dicts."
+  :context :request)
+
+(define-io-primitive "get-children"
+  :params (&key parent-type parent-id)
+  :returns "list"
+  :async true
+  :doc "Fetch child entities for a parent."
+  :context :request)
+
+(define-io-primitive "relations-from"
+  :params (entity-type)
+  :returns "list"
+  :async false
+  :doc "List of RelationDef dicts for an entity type."
+  :context :config)
+
+
+;; --------------------------------------------------------------------------
+;; Layout context providers — per-service header/page context
 ;; --------------------------------------------------------------------------
 
 ;; Shared across all services (root layout)