Convert all 23 register_custom_layout calls to register_sx_layout across 6 services

Layout defcomps are now fully self-contained via IO-primitive auto-fetch
macros, eliminating Python layout functions that manually threaded context
values through SxExpr wrappers.

Services converted:
- Federation (1 layout): social
- Blog (7 layouts): blog, blog-settings, blog-cache, blog-snippets,
  blog-menu-items, blog-tag-groups, blog-tag-group-edit
- SX docs (2 layouts): sx, sx-section
- Cart (2 layouts): cart-page, cart-admin + orders/order-detail
- Events (9 layouts): calendar-admin, slots, slot, day-admin, entry,
  entry-admin, ticket-types, ticket-type, markets
- Market (2 layouts): market, market-admin

New IO primitives added to shared/sx/primitives_io.py:
- federation-actor-ctx, cart-page-ctx, request-view-args
- events-calendar-ctx, events-day-ctx, events-entry-ctx,
  events-slot-ctx, events-ticket-type-ctx
- market-header-ctx (pre-builds desktop/mobile nav as SxExpr)

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

sx/sx/layouts.sx

@@ -1,17 +1,92 @@
-;; SX docs layout defcomps — root header via ~root-header-auto,
-;; sx-specific headers passed as &key params.
+;; SX docs layout defcomps — fully self-contained via IO primitives.
+;; Registered via register_sx_layout in __init__.py.
 
-;; --- SX home layout: root + sx menu row ---
+;; --- Main nav defcomp: static nav items from MAIN_NAV ---
+;; @css aria-selected:bg-violet-200 aria-selected:text-violet-900
 
-(defcomp ~sx-layout-full (&key sx-row)
+(defcomp ~sx-main-nav (&key section)
+  (let* ((sc "aria-selected:bg-violet-200 aria-selected:text-violet-900")
+         (items (list
+           (dict :label "Docs" :href "/docs/introduction")
+           (dict :label "Reference" :href "/reference/")
+           (dict :label "Protocols" :href "/protocols/wire-format")
+           (dict :label "Examples" :href "/examples/click-to-load")
+           (dict :label "Essays" :href "/essays/sx-sucks"))))
+    (<> (map (lambda (item)
+      (~nav-link
+        :href (get item "href")
+        :label (get item "label")
+        :is-selected (when (= (get item "label") section) "true")
+        :select-colours sc))
+      items))))
+
+;; --- SX header row ---
+
+(defcomp ~sx-header-row (&key nav child oob)
+  (~menu-row-sx :id "sx-row" :level 1 :colour "violet"
+    :link-href "/" :link-label "sx"
+    :link-label-content (~sx-docs-label)
+    :nav nav
+    :child-id "sx-header-child"
+    :child child
+    :oob oob))
+
+;; --- Sub-row for section pages ---
+
+(defcomp ~sx-sub-row (&key sub-label sub-href sub-nav selected oob)
+  (~menu-row-sx :id "sx-sub-row" :level 2 :colour "violet"
+    :link-href sub-href :link-label sub-label
+    :selected selected
+    :nav sub-nav
+    :oob oob))
+
+;; ---------------------------------------------------------------------------
+;; SX home layout (root + sx header)
+;; ---------------------------------------------------------------------------
+
+(defcomp ~sx-layout-full (&key section)
   (<> (~root-header-auto)
-    sx-row))
+    (~sx-header-row :nav (~sx-main-nav :section section))))
 
-(defcomp ~sx-layout-oob (&key root-header sx-row)
-  (<> root-header sx-row))
+(defcomp ~sx-layout-oob (&key section)
+  (<> (~sx-header-row
+        :nav (~sx-main-nav :section section)
+        :oob true)
+    (~clear-oob-div :id "sx-header-child")
+    (~root-header-auto true)))
 
-;; --- SX section layout: root + sx row (with child sub-row) ---
+(defcomp ~sx-layout-mobile (&key section)
+  (<> (~mobile-menu-section
+        :label "sx" :href "/" :level 1 :colour "violet"
+        :items (~sx-main-nav :section section))
+    (~root-mobile-auto)))
 
-(defcomp ~sx-section-layout-full (&key sx-row)
+;; ---------------------------------------------------------------------------
+;; SX section layout (root + sx header + sub-row)
+;; ---------------------------------------------------------------------------
+
+(defcomp ~sx-section-layout-full (&key section sub-label sub-href sub-nav selected)
   (<> (~root-header-auto)
-    sx-row))
+    (~sx-header-row
+      :nav (~sx-main-nav :section section)
+      :child (~sx-sub-row :sub-label sub-label :sub-href sub-href
+                          :sub-nav sub-nav :selected selected))))
+
+(defcomp ~sx-section-layout-oob (&key section sub-label sub-href sub-nav selected)
+  (<> (~sx-sub-row :sub-label sub-label :sub-href sub-href
+                   :sub-nav sub-nav :selected selected :oob true)
+    (~sx-header-row
+      :nav (~sx-main-nav :section section)
+      :oob true)
+    (~root-header-auto true)))
+
+(defcomp ~sx-section-layout-mobile (&key section sub-label sub-href sub-nav)
+  (<>
+    (when sub-nav
+      (~mobile-menu-section
+        :label (or sub-label section) :href sub-href :level 2 :colour "violet"
+        :items sub-nav))
+    (~mobile-menu-section
+      :label "sx" :href "/" :level 1 :colour "violet"
+      :items (~sx-main-nav :section section))
+    (~root-mobile-auto)))