refactor(context): trim replay cap plumbing

tests/agent/conftest.py

@@ -38,7 +38,6 @@ def make_loop(
     model: str = "test-model",
     context_window_tokens: int = 128_000,
     session_ttl_minutes: int = 0,
-    max_messages: int = 120,
     unified_session: bool = False,
     mcp_servers: dict | None = None,
     tools_config=None,
@@ -64,7 +63,6 @@ def make_loop(
         model=model,
         context_window_tokens=context_window_tokens,
         session_ttl_minutes=session_ttl_minutes,
-        max_messages=max_messages,
         unified_session=unified_session,
     )
     if mcp_servers is not None:
@@ -79,8 +77,8 @@ def make_loop(
     if patch_deps:
         with patch("nanobot.agent.loop.ContextBuilder"), \
              patch("nanobot.agent.loop.SessionManager"), \
-             patch("nanobot.agent.loop.SubagentManager") as MockSubMgr:
-            MockSubMgr.return_value.cancel_by_session = AsyncMock(return_value=0)
+             patch("nanobot.agent.loop.SubagentManager") as mock_sub_mgr:
+            mock_sub_mgr.return_value.cancel_by_session = AsyncMock(return_value=0)
             return AgentLoop(**kwargs)
     return AgentLoop(**kwargs)