The subtask card status machine matched only three English prefixes (`Task
Succeeded. Result:`, `Task failed.`, `Task timed out`). Anything else fell
through to `in_progress`, so a `task` tool error wrapped by
`ToolErrorHandlingMiddleware` (`Error: Tool 'task' failed ...`) left the card
spinning forever even after the run had ended.
Extract the prefix logic into `parseSubtaskResult` and recognise any leading
`Error:` token as a terminal failure. The extracted function is unit-tested
against the legacy prefixes plus the `AsyncCallbackManager` regression
captured in the upstream issue.
Refs: bytedance/deer-flow#3107 (BUG-007)
fancyboi999