[Bug]: REST tenant routes are mounted before path_prefix, so tenant requests from the SDK client get 404 #1376

What happened?

With a non-empty path_prefix, create_rest_routes serves the tenant routes in front of the prefix, at /{tenant}{path_prefix}/.... The SDK's own REST client sends the tenant after the prefix, at {path_prefix}/{tenant}/..., so a client whose AgentInterface sets tenant gets a 404 on every call.

In src/a2a/server/routes/rest_routes.py, the tenant routes come from Mount(path='/{tenant}', routes=base_route_objects), and base_route_objects already include path_prefix. On the client side, RestTransport._get_path returns /{tenant}{base_path}, which is appended to the interface URL. The HTTP bindings in a2a.proto also put the tenant right after the interface URL (post: "/{tenant}/message:send"). The hello_world_agent sample serves REST with path_prefix='/a2a/rest' and advertises an interface URL ending in /a2a/rest, so the prefix is meant to be part of the interface URL.

This changed in #892. Before it, the REST adapter built /{tenant}{path} and the FastAPI app added rpc_url in front, so the prefix came first. Without a prefix both layouts are the same, so only servers that set path_prefix are affected.

To reproduce, pip install "a2a-sdk[http-server]==1.2.3" and run:

import asyncio
from unittest.mock import AsyncMock

import httpx
from starlette.applications import Starlette

from a2a.client import ClientConfig, ClientFactory
from a2a.server.request_handlers import RequestHandler
from a2a.server.routes import create_rest_routes
from a2a.types import AgentCard, AgentInterface, ListTasksRequest, ListTasksResponse

handler = AsyncMock(spec=RequestHandler)
handler.on_list_tasks.return_value = ListTasksResponse()
app = Starlette(routes=create_rest_routes(handler, path_prefix="/a2a/rest"))

card = AgentCard(supported_interfaces=[AgentInterface(
    url="http://test/a2a/rest", protocol_binding="HTTP+JSON",
    protocol_version="1.0", tenant="acme")])


async def main():
    async with httpx.AsyncClient(transport=httpx.ASGITransport(app=app), base_url="http://test") as http:
        for path in ("/a2a/rest/acme/tasks", "/acme/a2a/rest/tasks"):
            r = await http.get(path, headers={"A2A-Version": "1.0"})
            print(path, r.status_code)
        client = ClientFactory(ClientConfig(httpx_client=http, supported_protocol_bindings=["HTTP+JSON"])).create(card)
        try:
            await client.list_tasks(ListTasksRequest())
            print("list_tasks: ok")
        except Exception as e:
            print(f"list_tasks: {type(e).__name__}: {e}")


asyncio.run(main())

I expected /a2a/rest/acme/tasks to return 200 and list_tasks to succeed.

I have a fix with a test and will open a PR.

Relevant log output

/a2a/rest/acme/tasks 404
/acme/a2a/rest/tasks 200
list_tasks: MethodNotFoundError: Resource not found: http://test/a2a/rest/acme/tasks

Code of Conduct

• I agree to follow this project's Code of Conduct