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/sxc/pages/helpers.py

@@ -15,7 +15,7 @@ async def _markets_admin_panel_sx(ctx: dict) -> str:
     """Render the markets list + create form panel."""
     from quart import g, url_for
     from shared.services.registry import services
-    from shared.sx.helpers import render_to_sx
+    from shared.sx.helpers import sx_call
     from shared.sx.parser import SxExpr
 
     rights = ctx.get("rights") or {}
@@ -32,30 +32,30 @@ async def _markets_admin_panel_sx(ctx: dict) -> str:
     form_html = ""
     if can_create:
         create_url = url_for("page_admin.create_market")
-        form_html = await render_to_sx("crud-create-form",
+        form_html = sx_call("crud-create-form",
                            create_url=create_url, csrf=csrf,
                            errors_id="market-create-errors",
                            list_id="markets-list",
                            placeholder="e.g. Suma, Craft Fair",
                            btn_label="Add market")
 
-    list_html = await _markets_admin_list_sx(ctx, markets)
-    return await render_to_sx("crud-panel",
+    list_html = _markets_admin_list_sx(ctx, markets)
+    return sx_call("crud-panel",
                   form=SxExpr(form_html), list=SxExpr(list_html),
                   list_id="markets-list")
 
 
-async def _markets_admin_list_sx(ctx: dict, markets: list) -> str:
+def _markets_admin_list_sx(ctx: dict, markets: list) -> str:
     """Render the markets list items."""
     from quart import url_for
     from shared.utils import route_prefix
-    from shared.sx.helpers import render_to_sx
+    from shared.sx.helpers import sx_call
     csrf_token = ctx.get("csrf_token")
     csrf = csrf_token() if callable(csrf_token) else (csrf_token or "")
     prefix = route_prefix()
 
     if not markets:
-        return await render_to_sx("empty-state",
+        return sx_call("empty-state",
                         message="No markets yet. Create one above.",
                         cls="text-gray-500 mt-4")
 
@@ -67,7 +67,7 @@ async def _markets_admin_list_sx(ctx: dict, markets: list) -> str:
         href = prefix + f"/{post_slug}/{m_slug}/"
         del_url = url_for("page_admin.delete_market", market_slug=m_slug)
         csrf_hdr = f'{{"X-CSRFToken":"{csrf}"}}'
-        parts.append(await render_to_sx("crud-item",
+        parts.append(sx_call("crud-item",
                             href=href, name=m_name, slug=m_slug,
                             del_url=del_url, csrf_hdr=csrf_hdr,
                             list_id="markets-list",
@@ -116,13 +116,13 @@ async def _h_all_markets_content(**kw):
                 page_info[p.id] = {"title": p.title, "slug": p.slug}
 
     if not markets:
-        return await _no_markets_sx()
+        return _no_markets_sx()
 
     prefix = route_prefix()
     next_url = prefix + url_for("all_markets.markets_fragment", page=page + 1)
 
-    cards = await _market_cards_sx(markets, page_info, page, has_more, next_url)
-    return await _markets_grid(cards)
+    cards = _market_cards_sx(markets, page_info, page, has_more, next_url)
+    return _markets_grid(cards)
 
 
 async def _h_page_markets_content(slug=None, **kw):
@@ -138,30 +138,30 @@ async def _h_page_markets_content(slug=None, **kw):
     post_slug = post.get("slug", "")
 
     if not markets:
-        return await _no_markets_sx("No markets for this page")
+        return _no_markets_sx("No markets for this page")
 
     prefix = route_prefix()
     next_url = prefix + url_for("page_markets.markets_fragment", page=page + 1)
 
-    cards = await _market_cards_sx(markets, {}, page, has_more, next_url,
+    cards = _market_cards_sx(markets, {}, page, has_more, next_url,
                                 show_page_badge=False, post_slug=post_slug)
-    return await _markets_grid(cards)
+    return _markets_grid(cards)
 
 
 async def _h_page_admin_content(slug=None, **kw):
     from shared.sx.page import get_template_context
-    from shared.sx.helpers import render_to_sx
+    from shared.sx.helpers import sx_call
     from shared.sx.parser import SxExpr
     ctx = await get_template_context()
     content = await _markets_admin_panel_sx(ctx)
-    return await render_to_sx("market-admin-content-wrap", inner=SxExpr(content))
+    return sx_call("market-admin-content-wrap", inner=SxExpr(content))
 
 
-async def _h_market_home_content(page_slug=None, market_slug=None, **kw):
+def _h_market_home_content(page_slug=None, market_slug=None, **kw):
     from quart import g
     post_data = getattr(g, "post_data", {})
     post = post_data.get("post", {})
-    return await _market_landing_content_sx(post)
+    return _market_landing_content_sx(post)
 
 
 def _h_market_admin_content(page_slug=None, market_slug=None, **kw):