feat: preserve CallToolResult.isError flag in MCPToolResult#1943
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feat: preserve CallToolResult.isError flag in MCPToolResult#1943Exploreunive wants to merge 1 commit intostrands-agents:mainfrom
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Addresses review feedback from strands-agents#1943: 1. **Clean split**: Only isError-related changes, no unrelated commits from AgentResult.text (PR strands-agents#1942) or other work. 2. **isError propagation**: MCPToolResult now exposes isError field: - True when MCP server reports CallToolResult.isError (application error) - True when a Python exception occurs during tool execution (protocol error) - False/absent on success Updated docstring clarifies both error sources. 3. **Exception propagation** (maintainer feedback from strands-agents#1670): MCPAgentTool.stream() now passes the original exception via ToolResultEvent(result, exception=e), matching the pattern used by decorated tools. Added _invoke_tool() helper that calls the MCP client internals directly to capture exceptions. Files changed: - mcp_types.py: Added isError: NotRequired[bool], updated docstring - mcp_client.py: Propagated isError in _handle_tool_result and _handle_tool_execution_error - mcp_agent_tool.py: Added _invoke_tool() for exception capture, stream() yields ToolResultEvent(result, exception=...) - Tests: Added isError assertions, exception propagation tests
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What
The
isErrorflag from MCP'sCallToolResultis now preserved in the framework'sMCPToolResult, enabling consumers to distinguish between:CallToolResult.isError=True)Previously, both error types ended up as
status="error"with no way to tell them apart.Changes
isError: NotRequired[bool]toMCPToolResultTypedDict inmcp_types.py_handle_tool_result()now propagatesisErrorfrom the MCPCallToolResult_handle_tool_execution_error()setsisError=Truefor execution exceptionsHow to test
All 53 tests pass (including new assertions for
isErrorin both success/error and exception scenarios).Fixes
Fixes #1670