Python: fix CopilotStudioAgent LineTooLong on large activities

python/packages/copilotstudio/agent_framework_copilotstudio/_agent.py

@@ -24,6 +24,13 @@
 
 from ._acquire_token import acquire_token
 
+# aiohttp caps how much it buffers while reading a single response line; at the default
+# read_bufsize this limit is 512 KB, which Copilot Studio can exceed for large activities
+# (for example, sizeable connector payloads), raising ``aiohttp.http_exceptions.LineTooLong``.
+# Copilot Studio streams each activity as one SSE ``data:`` line, so we raise the buffer to
+# lift that per-line limit well above the default. See https://github.com/microsoft/agent-framework/issues/7257.
+DEFAULT_READ_BUFSIZE = 1024 * 1024
+
 
 class CopilotStudioSettings(TypedDict, total=False):
     """Copilot Studio model settings.
@@ -70,6 +77,7 @@ def __init__(
         cloud: PowerPlatformCloud | None = None,
         agent_type: AgentType | None = None,
         custom_power_platform_cloud: str | None = None,
+        client_session_settings: dict[str, Any] | None = None,
         username: str | None = None,
         token_cache: Any | None = None,
         scopes: list[str] | None = None,
@@ -105,6 +113,12 @@ def __init__(
             agent_type: The type of Copilot Studio agent (Copilot, Agent, etc.).
             custom_power_platform_cloud: Custom Power Platform cloud URL if using
                 a custom environment.
+            client_session_settings: Optional keyword arguments forwarded to the underlying
+                aiohttp ``ClientSession`` used by the created client. Only applied when the agent
+                builds the client internally (ignored when ``client`` or ``settings`` is provided).
+                Defaults to ``read_bufsize`` of ``DEFAULT_READ_BUFSIZE`` (1 MiB) so large Copilot
+                Studio activities do not trigger ``aiohttp`` ``LineTooLong`` errors; override
+                ``read_bufsize`` here to raise or lower that limit.
             username: Optional username for token acquisition.
             token_cache: Optional token cache for storing authentication tokens.
             scopes: Optional list of authentication scopes. Defaults to Power Platform
@@ -150,12 +164,15 @@ def __init__(
                         "or 'COPILOTSTUDIOAGENT__SCHEMANAME' environment variable."
                     )
 
+                resolved_session_settings: dict[str, Any] = dict(client_session_settings or {})
+                resolved_session_settings.setdefault("read_bufsize", DEFAULT_READ_BUFSIZE)
                 settings = ConnectionSettings(
                     environment_id=resolved_environment_id,
                     agent_identifier=resolved_agent_identifier,
                     cloud=cloud,
                     copilot_agent_type=agent_type,
                     custom_power_platform_cloud=custom_power_platform_cloud,
+                    client_session_settings=resolved_session_settings,
                 )
 
             if not token:

python/packages/copilotstudio/pyproject.toml

@@ -24,7 +24,7 @@ classifiers = [
 ]
 dependencies = [
     "agent-framework-core>=1.11.0,<2",
-    "microsoft-agents-copilotstudio-client>=0.3.1,<0.3.2",
+    "microsoft-agents-copilotstudio-client>=1.2.0,<2",
 ]
 
 [tool.uv]

python/packages/copilotstudio/tests/test_copilot_agent.py

@@ -9,6 +9,7 @@
 from microsoft_agents.copilotstudio.client import CopilotClient
 
 from agent_framework_copilotstudio import CopilotStudioAgent
+from agent_framework_copilotstudio._agent import DEFAULT_READ_BUFSIZE
 
 
 def create_async_generator(items: list[Any]) -> Any:
@@ -98,6 +99,39 @@ def test_init_with_client(self, mock_copilot_client: MagicMock) -> None:
         assert agent.client == mock_copilot_client
         assert agent.id is not None
 
+    def test_init_applies_default_read_bufsize(self) -> None:
+        """The internally built client raises aiohttp's per-line limit to avoid LineTooLong (issue #7257)."""
+        agent = CopilotStudioAgent(
+            environment_id="env-id",
+            agent_identifier="agent-id",
+            token="fake-token",
+        )
+        assert agent.client.settings.client_session_settings["read_bufsize"] == DEFAULT_READ_BUFSIZE
+
+    def test_init_respects_custom_client_session_settings(self) -> None:
+        """User-provided client_session_settings are honored, and other keys are preserved."""
+        agent = CopilotStudioAgent(
+            environment_id="env-id",
+            agent_identifier="agent-id",
+            token="fake-token",
+            client_session_settings={"read_bufsize": 123, "trust_env": True},
+        )
+        session_settings = agent.client.settings.client_session_settings
+        assert session_settings["read_bufsize"] == 123
+        assert session_settings["trust_env"] is True
+
+    def test_init_injects_default_read_bufsize_into_partial_settings(self) -> None:
+        """When client_session_settings omits read_bufsize, the default is added without dropping other keys."""
+        agent = CopilotStudioAgent(
+            environment_id="env-id",
+            agent_identifier="agent-id",
+            token="fake-token",
+            client_session_settings={"trust_env": True},
+        )
+        session_settings = agent.client.settings.client_session_settings
+        assert session_settings["read_bufsize"] == DEFAULT_READ_BUFSIZE
+        assert session_settings["trust_env"] is True
+
     @patch("agent_framework_copilotstudio._acquire_token.acquire_token")
     def test_init_empty_environment_id(self, mock_acquire_token: MagicMock) -> None:
         mock_acquire_token.return_value = "fake-token"