fix: pass rpc_url='/' to create_jsonrpc_routes (a2a-sdk 1.x requirement)

7th a2a-sdk migration find from the v0 → v1 transition.
create_jsonrpc_routes() now requires rpc_url as a positional arg
(was implicit at root in 0.x). Pass '/' to match
a2a.utils.constants.DEFAULT_RPC_URL — that's also what
workspace-server's a2a_proxy.go forwards to (POSTs to workspace URL
without appending a path).

Symptom before fix: every workspace startup crashed with
  TypeError: create_jsonrpc_routes() missing 1 required positional
  argument: 'rpc_url'

Caught by harness 9 phase 4 (claude-code + langgraph both on
0.1.24). The user's "use langgraph for fast iteration" call cut
the diagnose cycle from 15min to ~30s — without that, this would
have taken another hermes round-trip to surface.

Updated reference_a2a_sdk_v0_to_v1_migration.md memory with this
entry alongside the previous 6 finds.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

workspace/main.py

@@ -242,10 +242,16 @@ async def main():  # pragma: no cover
         agent_card=agent_card,
     )
 
-    # v1: replace A2AStarletteApplication with Starlette route factory
+    # v1: replace A2AStarletteApplication with Starlette route factory.
+    # rpc_url is required in a2a-sdk 1.x (was implicit at root in 0.x).
+    # Use '/' to match a2a.utils.constants.DEFAULT_RPC_URL — that's also
+    # what the platform's a2a_proxy.go POSTs to (it forwards to the
+    # workspace's URL without appending a path). Card endpoint stays at
+    # the well-known path /.well-known/agent-card.json (handled by
+    # create_agent_card_routes default).
     routes = []
     routes.extend(create_agent_card_routes(agent_card))
-    routes.extend(create_jsonrpc_routes(request_handler=handler))
+    routes.extend(create_jsonrpc_routes(request_handler=handler, rpc_url="/"))
     app = Starlette(routes=routes)
 
     # 8. Register with platform