session/resume and session/close are gated as unstable and unreachable for v1 through AgentProtocolRouter #160

agent-client-protocol 1.0.0rc2.

• Agent.resume_session and Agent.close_session are declared with unstable=True (acp/interfaces.py), so they are only routed when the agent is attached with use_unstable_protocol=True. The v1 schema's stable meta.json lists both session/resume and session/close.
• AgentProtocolRouter attaches the v1 agent with V1AgentSideConnection.attach(self._v1_agent, connection) (acp/experimental/negotiation.py) and has no way to pass use_unstable_protocol. Through the router, a v1 client calling session/resume or session/close gets "Method not found" even when the agent implements them.

Expected: stable methods routed by default, and the router able to pass the flag to the v1 attachment.