Documents API error where multiple tool_result blocks are sent with
the same tool_use_id when a tool fails. The "Sibling tool call errored"
message is incorrectly being sent for the same tool that failed,
rather than only for other sibling tools in a parallel batch.
Includes:
- Root cause analysis
- Example JSON from reported incidents
- Suggested fix locations and pseudocode
- Related request IDs for debugging
