fix: guard TaskPlanPanel against missing tasks/events arrays - #556
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Restored subtask_execution history messages may omit the tasks or events arrays when the backend's buffered delegation plan could not be matched to its response (e.g. delegate_tasks invoked via execute_tool wrapper). The omitempty JSON tag causes the field to be absent entirely. Before this fix, TaskPlanPanel's useMemo iterated data.tasks with for...of, which throws 'TypeError: tasks is not iterable' on undefined, crashing the entire chat render to a blank screen. Guard both iterations with Array.isArray() fallback to []. Add regression test that reproduces the exact crash condition.
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Problem
Opening a chat session that contains a
delegate_tasksdelegation (invoked via theexecute_toolwrapper) causes a blank screen with:Root Cause
When Studio reconstructs session history,
buildSubTaskExecutionMessageinchat_utils.gomay produce asubtask_executionmessage whereTasksis nil — this happens when the buffered delegation plan cannot be matched to its response (e.g.delegate_tasksinvoked through theexecute_toolcatalog wrapper, or the response carries no per-task results).The
StudioMessage.Tasksfield hasjson:"tasks,omitempty", so a nil slice is omitted entirely from the JSON. On the client,TaskPlanPanel.tsxiteratesdata.taskswithfor...ofinside auseMemo—for...of undefinedthrowsTypeError: tasks is not iterable, and since it happens during render, React unmounts the whole tree → blank screen.Fix
Guard both
data.tasksanddata.eventsiterations inTaskPlanPanelwithArray.isArray()fallback to[]. A malformed or incomplete history message now renders as an empty task panel instead of crashing the entire chat.Files Changed
web/src/components/chat/TaskPlanPanel.tsx— defensive guard ondata.tasksanddata.eventsweb/src/components/chat/__tests__/TaskPlanPanel.test.tsx— regression test that reproduces the exactTypeError: data.tasks is not iterablecrashTesting
The new test fails against the pre-fix code with the identical error from the bug report and passes with the guard applied.