Add widget registry for universal UI decoupling

Introduces a widget system where domains register UI fragments into
named slots (container_nav, container_card, account_page, account_link).
Host apps iterate widgets generically without naming any domain.

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

services/widgets/__init__.py

@@ -0,0 +1,22 @@
+"""Per-domain widget registration.
+
+Called once at startup after domain services are registered.
+Only registers widgets for domains that are actually available.
+"""
+from __future__ import annotations
+
+
+def register_all_widgets() -> None:
+    from shared.services.registry import services
+
+    if services.has("calendar"):
+        from .calendar_widgets import register_calendar_widgets
+        register_calendar_widgets()
+
+    if services.has("market"):
+        from .market_widgets import register_market_widgets
+        register_market_widgets()
+
+    if services.has("cart"):
+        from .cart_widgets import register_cart_widgets
+        register_cart_widgets()

services/widgets/calendar_widgets.py

@@ -0,0 +1,91 @@
+"""Calendar-domain widgets: entries nav, calendar links, card entries, account pages."""
+from __future__ import annotations
+
+from shared.contracts.widgets import NavWidget, CardWidget, AccountPageWidget
+from shared.services.widget_registry import widgets
+from shared.services.registry import services
+
+
+# -- container_nav: associated entries ----------------------------------------
+
+async def _nav_entries_context(
+    session, *, container_type, container_id, post_slug, page=1, **kw,
+):
+    entries, has_more = await services.calendar.associated_entries(
+        session, container_type, container_id, page,
+    )
+    return {
+        "entries": entries,
+        "has_more": has_more,
+        "page": page,
+        "post_slug": post_slug,
+    }
+
+
+# -- container_nav: calendar links -------------------------------------------
+
+async def _nav_calendars_context(
+    session, *, container_type, container_id, post_slug, **kw,
+):
+    calendars = await services.calendar.calendars_for_container(
+        session, container_type, container_id,
+    )
+    return {"calendars": calendars, "post_slug": post_slug}
+
+
+# -- container_card: confirmed entries for post listings ----------------------
+
+async def _card_entries_batch(session, post_ids):
+    return await services.calendar.confirmed_entries_for_posts(session, post_ids)
+
+
+# -- account pages: tickets & bookings ---------------------------------------
+
+async def _tickets_context(session, *, user_id, **kw):
+    tickets = await services.calendar.user_tickets(session, user_id=user_id)
+    return {"tickets": tickets}
+
+
+async def _bookings_context(session, *, user_id, **kw):
+    bookings = await services.calendar.user_bookings(session, user_id=user_id)
+    return {"bookings": bookings}
+
+
+# -- registration entry point ------------------------------------------------
+
+def register_calendar_widgets() -> None:
+    widgets.add_container_nav(NavWidget(
+        domain="calendar",
+        order=10,
+        context_fn=_nav_entries_context,
+        template="_widgets/container_nav/calendar_entries.html",
+    ))
+    widgets.add_container_nav(NavWidget(
+        domain="calendar_links",
+        order=20,
+        context_fn=_nav_calendars_context,
+        template="_widgets/container_nav/calendar_links.html",
+    ))
+    widgets.add_container_card(CardWidget(
+        domain="calendar",
+        order=10,
+        batch_fn=_card_entries_batch,
+        context_key="associated_entries",
+        template="_widgets/container_card/calendar_entries.html",
+    ))
+    widgets.add_account_page(AccountPageWidget(
+        domain="calendar",
+        slug="tickets",
+        label="tickets",
+        order=20,
+        context_fn=_tickets_context,
+        template="_types/auth/_tickets_panel.html",
+    ))
+    widgets.add_account_page(AccountPageWidget(
+        domain="calendar",
+        slug="bookings",
+        label="bookings",
+        order=30,
+        context_fn=_bookings_context,
+        template="_types/auth/_bookings_panel.html",
+    ))

services/widgets/cart_widgets.py

@@ -0,0 +1,15 @@
+"""Cart-domain widgets: orders link on account page."""
+from __future__ import annotations
+
+from shared.contracts.widgets import AccountNavLink
+from shared.services.widget_registry import widgets
+from shared.infrastructure.urls import cart_url
+
+
+def register_cart_widgets() -> None:
+    widgets.add_account_link(AccountNavLink(
+        label="orders",
+        order=100,
+        href_fn=lambda: cart_url("/orders/"),
+        external=True,
+    ))

services/widgets/market_widgets.py

@@ -0,0 +1,24 @@
+"""Market-domain widgets: marketplace links on container pages."""
+from __future__ import annotations
+
+from shared.contracts.widgets import NavWidget
+from shared.services.widget_registry import widgets
+from shared.services.registry import services
+
+
+async def _nav_markets_context(
+    session, *, container_type, container_id, post_slug, **kw,
+):
+    markets = await services.market.marketplaces_for_container(
+        session, container_type, container_id,
+    )
+    return {"markets": markets, "post_slug": post_slug}
+
+
+def register_market_widgets() -> None:
+    widgets.add_container_nav(NavWidget(
+        domain="market",
+        order=30,
+        context_fn=_nav_markets_context,
+        template="_widgets/container_nav/market_links.html",
+    ))