Add fragment router for micro-frontend composition

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

app/__init__.py

@@ -164,12 +164,13 @@ def create_app() -> FastAPI:
         return JSONResponse({"detail": "Not found"}, status_code=404)
 
     # Include routers
-    from .routers import auth, storage, api, recipes, cache, runs, home, effects, inbox
+    from .routers import auth, storage, api, recipes, cache, runs, home, effects, inbox, fragments
 
     # Home and auth routers (root level)
     app.include_router(home.router, tags=["home"])
     app.include_router(auth.router, prefix="/auth", tags=["auth"])
     app.include_router(inbox.router, tags=["inbox"])
+    app.include_router(fragments.router, tags=["fragments"])
 
     # Feature routers
     app.include_router(storage.router, prefix="/storage", tags=["storage"])

app/routers/fragments.py

@@ -0,0 +1,27 @@
+"""
+Art-DAG fragment endpoints.
+
+Exposes HTML fragments at ``/internal/fragments/{type}`` for consumption
+by coop apps via the fragment client.
+"""
+
+from fastapi import APIRouter, Request, Response
+
+router = APIRouter()
+
+# Registry of fragment handlers: type -> async callable(request) returning HTML str
+_handlers: dict[str, object] = {}
+
+FRAGMENT_HEADER = "X-Fragment-Request"
+
+
+@router.get("/internal/fragments/{fragment_type}")
+async def get_fragment(fragment_type: str, request: Request):
+    if not request.headers.get(FRAGMENT_HEADER):
+        return Response(content="", status_code=403)
+
+    handler = _handlers.get(fragment_type)
+    if handler is None:
+        return Response(content="", media_type="text/html", status_code=200)
+    html = await handler(request)
+    return Response(content=html, media_type="text/html", status_code=200)