From 036fa6009538548ce70426d3ad42e6092ac6f067 Mon Sep 17 00:00:00 2001 From: Nilay <118994073+NilayYadav@users.noreply.github.com> Date: Wed, 29 Jul 2026 04:11:47 +0530 Subject: [PATCH] Studio: pass raise_on_error=False on the stdio MCP call path (#7517) --- studio/backend/core/inference/mcp_client.py | 7 ++- .../backend/tests/test_mcp_flatten_result.py | 43 +++++++++++++++++++ .../backend/tests/test_mcp_stdio_sessions.py | 40 +++++++++++++---- 3 files changed, 81 insertions(+), 9 deletions(-) diff --git a/studio/backend/core/inference/mcp_client.py b/studio/backend/core/inference/mcp_client.py index 0256df944e..98112c6d5b 100644 --- a/studio/backend/core/inference/mcp_client.py +++ b/studio/backend/core/inference/mcp_client.py @@ -971,7 +971,12 @@ def _call_stdio_tool( raise RuntimeError("MCP server connection is not available") else: rem = _remaining() - coro = _race_tool_call(session.client.call_tool(name, args), rem, cancel_event) + # raise_on_error=False for the same reason as the one-shot path. + coro = _race_tool_call( + session.client.call_tool(name, args, raise_on_error = False), + rem, + cancel_event, + ) return session.run(coro, rem) except (_MCPCancelled, asyncio.TimeoutError): # _race_tool_call cancels the pending call but cancellation is diff --git a/studio/backend/tests/test_mcp_flatten_result.py b/studio/backend/tests/test_mcp_flatten_result.py index 7daee799f9..618c5ccfe6 100644 --- a/studio/backend/tests/test_mcp_flatten_result.py +++ b/studio/backend/tests/test_mcp_flatten_result.py @@ -175,3 +175,46 @@ def test_call_tool_sync_passes_raise_on_error_false_and_keeps_error_images(monke assert out.startswith("Error: boom") assert MCP_IMAGES_SENTINEL in out assert is_tool_error(out) + + +def test_stdio_session_call_also_passes_raise_on_error_false(monkeypatch): + seen = {} + + class _FakeStdioClient: + def __init__(self): + self.connected = False + self.transport = SimpleNamespace(_is_session_dead = lambda: False) + + async def __aenter__(self): + self.connected = True + return self + + async def __aexit__(self, *exc): + self.connected = False + + def is_connected(self): + return self.connected + + async def call_tool( + self, + name, + args, + raise_on_error = True, + ): + seen["raise_on_error"] = raise_on_error + return _result(_text("boom"), _image(), is_error = True) + + monkeypatch.setattr( + mcp_client, "_client", lambda url, headers, use_oauth = False: _FakeStdioClient() + ) + try: + out = call_tool_sync( + "npx fake-stdio-server", None, "take_screenshot", {}, scope = "s=p:t=thread1" + ) + finally: + mcp_client.close_stdio_sessions() + + assert seen["raise_on_error"] is False + assert out.startswith("Error: boom") + assert MCP_IMAGES_SENTINEL in out + assert is_tool_error(out) diff --git a/studio/backend/tests/test_mcp_stdio_sessions.py b/studio/backend/tests/test_mcp_stdio_sessions.py index d714d9d640..37c812677a 100644 --- a/studio/backend/tests/test_mcp_stdio_sessions.py +++ b/studio/backend/tests/test_mcp_stdio_sessions.py @@ -60,7 +60,12 @@ class FakeClient: def is_connected(self) -> bool: return self.connected - async def call_tool(self, name: str, args: dict): + async def call_tool( + self, + name: str, + args: dict, + raise_on_error: bool = True, + ): if self.call_delay: await asyncio.sleep(self.call_delay) if self.fail_next: @@ -120,10 +125,15 @@ def test_tool_error_does_not_recycle_session(fake_clients, monkeypatch): from fastmcp.exceptions import ToolError class ToolFailure(FakeClient): - async def call_tool(self, name, args): + async def call_tool( + self, + name, + args, + raise_on_error = True, + ): if name == "boom": raise ToolError("tool exploded") # tool-level: session stays connected - return await super().call_tool(name, args) + return await super().call_tool(name, args, raise_on_error) monkeypatch.setattr( mcp_client, "_client", lambda url, headers, use_oauth = False: ToolFailure(url) @@ -441,12 +451,17 @@ def test_overlapping_calls_serialize_on_shared_session(fake_clients, monkeypatch active = 0 max_active = 0 - async def call_tool(self, name, args): + async def call_tool( + self, + name, + args, + raise_on_error = True, + ): OverlapDetect.active += 1 OverlapDetect.max_active = max(OverlapDetect.max_active, OverlapDetect.active) try: await asyncio.sleep(0.2) - return await super().call_tool(name, args) + return await super().call_tool(name, args, raise_on_error) finally: OverlapDetect.active -= 1 @@ -473,9 +488,14 @@ def test_timeout_budget_spans_connect_and_call(fake_clients, monkeypatch): await asyncio.sleep(0.4) return await super().__aenter__() - async def call_tool(self, name, args): + async def call_tool( + self, + name, + args, + raise_on_error = True, + ): await asyncio.sleep(0.5) - return await super().call_tool(name, args) + return await super().call_tool(name, args, raise_on_error) monkeypatch.setattr(mcp_client, "_client", lambda url, headers, use_oauth = False: SlowBoth(url)) start = time.monotonic() @@ -565,7 +585,11 @@ def test_execute_tool_config_check_tracks_row(tmp_path, monkeypatch): def test_multi_block_result_flattens_through_session(fake_clients): - async def _rich_call(name, args): + async def _rich_call( + name, + args, + raise_on_error = True, + ): return SimpleNamespace( content = [ SimpleNamespace(type = "text", text = "### Page"),