fix(acp): declare session load and resume capabilities in initialize response (#6985)

The resume_session and load_session handlers were implemented but undiscoverable by ACP clients because the capabilities weren't declared in the initialize response. Adds load_session=True and resume=SessionResumeCapabilities() plus wire-format tests. Fixes #6633. Contributed by @luyao618.

acp_adapter/server.py

@@ -36,6 +36,7 @@ from acp.schema import (
     SessionCapabilities,
     SessionForkCapabilities,
     SessionListCapabilities,
+    SessionResumeCapabilities,
     SessionInfo,
     TextContentBlock,
     UnstructuredCommandInput,
@@ -245,9 +246,11 @@ class HermesACPAgent(acp.Agent):
             protocol_version=acp.PROTOCOL_VERSION,
             agent_info=Implementation(name="hermes-agent", version=HERMES_VERSION),
             agent_capabilities=AgentCapabilities(
+                load_session=True,
                 session_capabilities=SessionCapabilities(
                     fork=SessionForkCapabilities(),
                     list=SessionListCapabilities(),
+                    resume=SessionResumeCapabilities(),
                 ),
             ),
             auth_methods=auth_methods,

tests/acp/test_server.py

@@ -68,9 +68,22 @@ class TestInitialize:
         resp = await agent.initialize(protocol_version=1)
         caps = resp.agent_capabilities
         assert isinstance(caps, AgentCapabilities)
+        assert caps.load_session is True
         assert caps.session_capabilities is not None
         assert caps.session_capabilities.fork is not None
         assert caps.session_capabilities.list is not None
+        assert caps.session_capabilities.resume is not None
+
+    @pytest.mark.asyncio
+    async def test_initialize_capabilities_wire_format(self, agent):
+        """Verify the JSON wire format uses correct aliases so ACP clients see the right keys."""
+        resp = await agent.initialize(protocol_version=1)
+        payload = resp.agent_capabilities.model_dump(by_alias=True, exclude_none=True)
+        assert payload["loadSession"] is True
+        session_caps = payload["sessionCapabilities"]
+        assert "fork" in session_caps
+        assert "list" in session_caps
+        assert "resume" in session_caps
 
 
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