Issue

Merge writes from the plugins did not include parent ids. This was a problem if no successful insert write proceeded the merge write for a particular span, because the span would be attached to the trace without a parent. Spans without parents automatically get is_root=true, so this can lead to a situation where a trace has multiple spans marked as the root.

Solution

Include the correct root_span_id and parent span IDs in every merge write, using the same deterministic hierarchy used by the corresponding insert. This allows a merge to preserve the span’s hierarchy even when the initial insert was not persisted, without requiring a sink-side identity cache.

Add regression coverage to verify that:

• Every merge carries the same trace and parent identity as its insert.
• Stateless updates for closed spans include their parent IDs.