Phase 7: Replace render_template() with s-expression rendering in all POST/PUT/DELETE routes

Eliminates all render_template() calls from POST/PUT/DELETE handlers across
all 7 services. Moves sexp_components.py into sexp/ packages per service.

- Blog: like toggle, snippets, cache clear, features/sumup/entry panels,
  create/delete market, WYSIWYG editor panel (render_editor_panel)
- Federation: like/unlike/boost/unboost, follow/unfollow, actor card,
  interaction buttons
- Events: ticket widget, checkin, confirm/decline/provisional, tickets
  config, posts CRUD, description edit/save, calendar/slot/ticket_type
  CRUD, payments, buy tickets, day main panel, entry page
- Market: like toggle, cart add response
- Account: newsletter toggle
- Cart: checkout error pages (3 handlers)
- Orders: checkout error page (1 handler)

Remaining render_template() calls are exclusively in GET handlers and
internal services (email templates, fragment endpoints).

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

orders/app.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 import path_setup  # noqa: F401  # adds shared/ to sys.path
-import sexp_components  # noqa: F401  # ensure Hypercorn --reload watches this file
+import sexp.sexp_components as sexp_components  # noqa: F401  # ensure Hypercorn --reload watches this file
 
 from pathlib import Path
 from types import SimpleNamespace
@@ -71,7 +71,7 @@ def create_app() -> "Quart":
     ])
 
     # Load orders-specific s-expression components
-    from sexp_components import load_orders_components
+    from sexp.sexp_components import load_orders_components
     load_orders_components()
 
     app.register_blueprint(register_fragments())

orders/bp/order/routes.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from quart import Blueprint, g, render_template, redirect, url_for, make_response
+from quart import Blueprint, g, redirect, url_for, make_response
 from sqlalchemy import select
 from sqlalchemy.orm import selectinload
 
@@ -48,7 +48,7 @@ def register() -> Blueprint:
         if not order:
             return await make_response("Order not found", 404)
 
-        from sexp_components import render_order_page, render_order_oob
+        from sexp.sexp_components import render_order_page, render_order_oob
 
         ctx = await get_template_context()
         calendar_entries = ctx.get("calendar_entries")
@@ -98,11 +98,10 @@ def register() -> Blueprint:
         await g.s.flush()
 
         if not hosted_url:
-            html = await render_template(
-                "_types/cart/checkout_error.html",
-                order=order,
-                error="No hosted checkout URL returned from SumUp when trying to reopen payment.",
-            )
+            from shared.sexp.page import get_template_context
+            from sexp.sexp_components import render_checkout_error_page
+            tctx = await get_template_context()
+            html = await render_checkout_error_page(tctx, error="No hosted checkout URL returned from SumUp when trying to reopen payment.", order=order)
             return await make_response(html, 500)
 
         return redirect(hosted_url)

orders/bp/orders/routes.py

@@ -117,7 +117,7 @@ def register(url_prefix: str) -> Blueprint:
         orders = result.scalars().all()
 
         from shared.sexp.page import get_template_context
-        from sexp_components import (
+        from sexp.sexp_components import (
             render_orders_page,
             render_orders_rows,
             render_orders_oob,

orders/sexp/sexp_components.py

@@ -15,7 +15,7 @@ from shared.sexp.helpers import (
     search_mobile_html, search_desktop_html, full_page, oob_page,
 )
 from shared.sexp.page import HAMBURGER_HTML
-from shared.infrastructure.urls import market_product_url
+from shared.infrastructure.urls import market_product_url, cart_url
 
 
 # ---------------------------------------------------------------------------
@@ -383,3 +383,56 @@ async def render_order_oob(ctx: dict, order: Any,
     )
 
     return oob_page(ctx, oobs_html=oobs, filter_html=filt, content_html=main)
+
+
+# ---------------------------------------------------------------------------
+# Public API: Checkout error
+# ---------------------------------------------------------------------------
+
+def _checkout_error_filter_html() -> str:
+    return (
+        '<header class="mb-6 sm:mb-8">'
+        '<h1 class="text-xl sm:text-2xl md:text-3xl font-semibold tracking-tight">'
+        'Checkout error</h1>'
+        '<p class="text-xs sm:text-sm text-stone-600">'
+        'We tried to start your payment with SumUp but hit a problem.</p>'
+        '</header>'
+    )
+
+
+def _checkout_error_content_html(error: str | None, order: Any | None) -> str:
+    err_msg = error or "Unexpected error while creating the hosted checkout session."
+    order_html = ""
+    if order:
+        order_html = (
+            f'<p class="text-xs text-rose-800/80">'
+            f'Order ID: <span class="font-mono">#{order.id}</span></p>'
+        )
+    back_url = cart_url("/")
+    return (
+        '<div class="max-w-full px-3 py-3 space-y-4">'
+        '<div class="rounded-2xl border border-rose-200 bg-rose-50/80 p-4 sm:p-6 text-sm text-rose-900 space-y-2">'
+        f'<p class="font-medium">Something went wrong.</p>'
+        f'<p>{err_msg}</p>'
+        f'{order_html}'
+        '</div>'
+        '<div>'
+        f'<a href="{back_url}"'
+        ' class="inline-flex items-center px-3 py-2 text-xs sm:text-sm rounded-full border border-stone-300 bg-white hover:bg-stone-50 transition">'
+        '<i class="fa fa-shopping-cart mr-2" aria-hidden="true"></i>'
+        'Back to cart</a>'
+        '</div>'
+        '</div>'
+    )
+
+
+async def render_checkout_error_page(ctx: dict, error: str | None = None, order: Any | None = None) -> str:
+    """Full page: checkout error."""
+    hdr = root_header_html(ctx)
+    hdr += sexp(
+        '(div :id "root-header-child" :class "flex flex-col w-full items-center" (raw! c))',
+        c=_auth_header_html(ctx),
+    )
+    filt = _checkout_error_filter_html()
+    content = _checkout_error_content_html(error, order)
+    return full_page(ctx, header_rows_html=hdr, filter_html=filt, content_html=content)