Slate v2 Op-family Twenty-sixth Slice

Supporting plan. For current queue and roadmap truth, see master-roadmap.md.

Goal

• Cash out explicit non-empty Range deletion across adjacent supported top-level block boundaries.

Scope

• Keep the slice to adjacent supported top-level block crossings only.
• Support:
  • explicit non-empty Range
  • current non-empty selection when at is omitted
• Keep same-type/same-props block merge requirements.
• Avoid wider multi-block range deletion in this slice.

Phases

• Confirm the adjacent cross-block range-delete semantics and current helper coverage
• Write focused failing tests
• Implement or confirm the smallest honest adjacent cross-block range-delete slice
• Sync package/public docs
• Verify the touched package/docs