Add macros, declarative handlers (defhandler), and convert all fragment routes to sx

Phase 1 — Macros: defmacro + quasiquote syntax (`, ,, ,@) in parser,
evaluator, HTML renderer, and JS mirror. Macro type, expansion, and
round-trip serialization.

Phase 2 — Expanded primitives: app-url, url-for, asset-url, config,
format-date, parse-int (pure); service, request-arg, request-path,
nav-tree, get-children (I/O); jinja-global, relations-from (pure).
Updated _io_service to accept (service "registry-name" "method" :kwargs)
with auto kebab→snake conversion. DTO-to-dict now expands datetime fields
into year/month/day convenience keys. Tuple returns converted to lists.

Phase 3 — Declarative handlers: HandlerDef type, defhandler special form,
handler registry (service → name → HandlerDef), async evaluator+renderer
(async_eval.py) that awaits I/O primitives inline within control flow.
Handler loading from .sx files, execute_handler, blueprint factory.

Phase 4 — Convert all fragment routes: 13 Python fragment handlers across
8 services replaced with declarative .sx handler files. All routes.py
simplified to uniform sx dispatch pattern. Two Jinja HTML handlers
(events/container-cards, events/account-page) kept as Python.

New files: shared/sx/async_eval.py, shared/sx/handlers.py,
shared/sx/tests/test_handlers.py, plus 13 handler .sx files under
{service}/sx/handlers/. MarketService.product_by_slug() added.

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

federation/bp/fragments/routes.py

@@ -2,6 +2,9 @@
 
 Exposes sx fragments at ``/internal/fragments/<type>`` for consumption
 by other coop apps via the fragment client.
+
+All handlers are defined declaratively in .sx files under
+``federation/sx/handlers/`` and dispatched via the sx handler registry.
 """
 
 from __future__ import annotations
@@ -9,13 +12,12 @@ from __future__ import annotations
 from quart import Blueprint, Response, request
 
 from shared.infrastructure.fragments import FRAGMENT_HEADER
+from shared.sx.handlers import get_handler, execute_handler
 
 
 def register():
     bp = Blueprint("fragments", __name__, url_prefix="/internal/fragments")
 
-    _handlers: dict[str, object] = {}
-
     @bp.before_request
     async def _require_fragment_header():
         if not request.headers.get(FRAGMENT_HEADER):
@@ -23,60 +25,12 @@ def register():
 
     @bp.get("/<fragment_type>")
     async def get_fragment(fragment_type: str):
-        handler = _handlers.get(fragment_type)
-        if handler is None:
-            return Response("", status=200, content_type="text/sx")
-        src = await handler()
-        return Response(src, status=200, content_type="text/sx")
-
-    # --- link-card fragment: actor profile preview card --------------------------
-
-    def _federation_link_card_sx(actor, link: str) -> str:
-        from shared.sx.helpers import sx_call
-        return sx_call("link-card",
-                         link=link,
-                         title=actor.display_name or actor.preferred_username,
-                         image=None,
-                         icon="fas fa-user",
-                         subtitle=f"@{actor.preferred_username}" if actor.preferred_username else None,
-                         detail=actor.summary,
-                         data_app="federation")
-
-    async def _link_card_handler():
-        from quart import g
-        from shared.services.registry import services
-        from shared.infrastructure.urls import federation_url
-
-        username = request.args.get("username", "")
-        slug = request.args.get("slug", "")
-        keys_raw = request.args.get("keys", "")
-
-        # Batch mode
-        if keys_raw:
-            usernames = [k.strip() for k in keys_raw.split(",") if k.strip()]
-            parts = []
-            for u in usernames:
-                parts.append(f"<!-- fragment:{u} -->")
-                actor = await services.federation.get_actor_by_username(g.s, u)
-                if actor:
-                    parts.append(_federation_link_card_sx(
-                        actor, federation_url(f"/users/{actor.preferred_username}"),
-                    ))
-            return "\n".join(parts)
-
-        # Single mode
-        lookup = username or slug
-        if not lookup:
-            return ""
-        actor = await services.federation.get_actor_by_username(g.s, lookup)
-        if not actor:
-            return ""
-        return _federation_link_card_sx(
-            actor, federation_url(f"/users/{actor.preferred_username}"),
-        )
-
-    _handlers["link-card"] = _link_card_handler
-
-    bp._fragment_handlers = _handlers
+        handler_def = get_handler("federation", fragment_type)
+        if handler_def is not None:
+            result = await execute_handler(
+                handler_def, "federation", args=dict(request.args),
+            )
+            return Response(result, status=200, content_type="text/sx")
+        return Response("", status=200, content_type="text/sx")
 
     return bp