Remove render_to_sx from public API: enforce sx_call for all service code

Replace ~250 render_to_sx calls across all services with sync sx_call,
converting many async functions to sync where no other awaits remained.
Make render_to_sx/render_to_sx_with_env private (_render_to_sx).
Add (post-header-ctx) IO primitive and shared post/post-admin defmacros.
Convert built-in post/post-admin layouts from Python to register_sx_layout
with .sx defcomps. Remove dead post_admin_mobile_nav_sx.

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

market/bp/all_markets/routes.py

@@ -47,7 +47,7 @@ def register() -> Blueprint:
         markets, has_more, page_info = await _load_markets(page)
 
         from sxc.pages.renders import render_all_markets_cards
-        sx_src = await render_all_markets_cards(markets, has_more, page_info, page)
+        sx_src = render_all_markets_cards(markets, has_more, page_info, page)
         return sx_response(sx_src)
 
     return bp

market/bp/browse/routes.py

@@ -58,7 +58,7 @@ def register():
           resp = await make_response(html)
       elif product_info["page"] > 1:
           tctx.update(product_info)
-          sx_src = await render_browse_cards(tctx)
+          sx_src = render_browse_cards(tctx)
           resp = sx_response(sx_src)
       else:
           sx_src = await render_browse_oob(tctx)
@@ -99,7 +99,7 @@ def register():
           resp = await make_response(html)
       elif product_info["page"] > 1:
           tctx.update(product_info)
-          sx_src = await render_browse_cards(tctx)
+          sx_src = render_browse_cards(tctx)
           resp = sx_response(sx_src)
       else:
           sx_src = await render_browse_oob(tctx)
@@ -140,7 +140,7 @@ def register():
           resp = await make_response(html)
       elif product_info["page"] > 1:
           tctx.update(product_info)
-          sx_src = await render_browse_cards(tctx)
+          sx_src = render_browse_cards(tctx)
           resp = sx_response(sx_src)
       else:
           sx_src = await render_browse_oob(tctx)

market/bp/page_markets/routes.py

@@ -32,7 +32,7 @@ def register() -> Blueprint:
 
         from sxc.pages.renders import render_page_markets_cards
         post_slug = post.get("slug", "")
-        sx_src = await render_page_markets_cards(markets, has_more, page, post_slug)
+        sx_src = render_page_markets_cards(markets, has_more, page, post_slug)
         return sx_response(sx_src)
 
     return bp

market/bp/product/routes.py

@@ -129,7 +129,7 @@ def register():
       from sxc.pages.renders import render_like_toggle_button
 
       if not g.user:
-          return sx_response(await render_like_toggle_button(product_slug, False), status=403)
+          return sx_response(render_like_toggle_button(product_slug, False), status=403)
 
       user_id = g.user.id
 
@@ -138,7 +138,7 @@ def register():
       })
       liked = result["liked"]
 
-      return sx_response(await render_like_toggle_button(product_slug, liked))
+      return sx_response(render_like_toggle_button(product_slug, liked))
 
 
 
@@ -257,7 +257,7 @@ def register():
             from sxc.pages.renders import render_cart_added_response
             item_data = getattr(g, "item_data", {})
             d = item_data.get("d", {})
-            return sx_response(await render_cart_added_response(g.cart, ci_ns, d))
+            return sx_response(render_cart_added_response(g.cart, ci_ns, d))
 
         # normal POST: go to cart page
         from shared.infrastructure.urls import cart_url