Slate v2 Op-family Eighteenth Slice

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

Goal

• Land the first honest collapsed-delete follow-on after the narrow Editor.before(...) / Editor.after(...) seam.

Scope

• Keep delete(...) same-text only for collapsed point/selection deletion.
• Support reverse.
• Support distance.
• Support:
  • explicit Point
  • current collapsed selection when at is omitted
• Keep explicit non-empty range deletion narrow and unchanged in this slice.
• Avoid cross-node deletion, unit, and hanging parity in this slice.

Phases

• Confirm the narrow collapsed-delete semantics and current text/location seams
• Write focused failing tests
• Implement the smallest honest core/API slice
• Sync package/public docs
• Verify the touched package/docs