Implement flexible entity relation system (Phases A–E)

Declarative relation registry via defrelation s-expressions with
cardinality enforcement (one-to-one, one-to-many, many-to-many),
registry-aware relate/unrelate/can-relate API endpoints, generic
container-nav fragment, and relation-driven UI components.

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

shared/sexp/components.py

@@ -36,6 +36,10 @@ def load_shared_components() -> None:
     register_components(_SEARCH_DESKTOP)
     register_components(_MOBILE_FILTER)
     register_components(_ORDER_SUMMARY_CARD)
+    # Relation-driven components
+    register_components(_RELATION_NAV)
+    register_components(_RELATION_ATTACH)
+    register_components(_RELATION_DETACH)
 
 
 # ---------------------------------------------------------------------------
@@ -768,3 +772,48 @@ _ORDER_SUMMARY_CARD = r'''
         (str (or currency "GBP") " " total-amount)
         "\u2013"))))
 '''
+
+
+# ---------------------------------------------------------------------------
+# ~relation-nav
+# ---------------------------------------------------------------------------
+
+_RELATION_NAV = '''
+(defcomp ~relation-nav (&key href name icon nav-class relation-type)
+  (a :href href :class (or nav-class "flex items-center gap-3 rounded-lg py-2 px-3 text-sm text-stone-700 hover:bg-stone-100 transition-colors")
+    (when icon
+      (div :class "w-8 h-8 rounded bg-stone-200 flex items-center justify-center flex-shrink-0"
+        (i :class icon :aria-hidden "true")))
+    (div :class "flex-1 min-w-0"
+      (div :class "font-medium truncate" name))))
+'''
+
+
+# ---------------------------------------------------------------------------
+# ~relation-attach
+# ---------------------------------------------------------------------------
+
+_RELATION_ATTACH = '''
+(defcomp ~relation-attach (&key create-url label icon)
+  (a :href create-url
+     :hx-get create-url
+     :hx-target "#main-panel"
+     :hx-swap "outerHTML"
+     :hx-push-url "true"
+     :class "flex items-center gap-2 text-sm p-2 rounded hover:bg-stone-100 text-stone-500 hover:text-stone-700 transition-colors"
+    (when icon (i :class icon))
+    (span (or label "Add"))))
+'''
+
+
+# ---------------------------------------------------------------------------
+# ~relation-detach
+# ---------------------------------------------------------------------------
+
+_RELATION_DETACH = '''
+(defcomp ~relation-detach (&key detach-url name)
+  (button :hx-delete detach-url
+          :hx-confirm (str "Remove " (or name "this item") "?")
+          :class "text-red-500 hover:text-red-700 text-sm p-1 rounded hover:bg-red-50 transition-colors"
+    (i :class "fa fa-times" :aria-hidden "true")))
+'''