Fill handle and range move

Fill handle is used for autofill, and range‑move is used for moving ranges.

1) Minimal UI contract

• Separate handle element with explicit mousedown.
• Explicit drag cycle: begin → update → commit.
• Escape cancels.

2) Example sequence

orchestration.fill.begin({ rowIndex: 0, colKey: "service" })
orchestration.fill.update({ rowIndex: 5, colKey: "service" })
orchestration.fill.commit()

3) Recommendations

• Do not combine drag‑move and fill on the same handle.
• Use visual hints for the range.
• Consider virtualization on drag over.