Slate v2 Op-family Twelfth Slice

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

Goal

• Broaden the first honest delete family cut in slate from exact { at: Path } to the next exact case: Point.

Scope

• Support exact point deletion only.
• Keep the slice narrow:
  • no range deletion
  • no unit/distance/reverse/hanging parity
  • no broad legacy delete(...) claim

Phases

• Confirm the exact point-delete semantics and current helper seam
• Write focused failing tests
• Implement the smallest honest delete broadening
• Sync package/public docs
• Verify the touched package/docs