refactor: Replace SortableJS 2/4: replace SortableJS with native HTML5 drag & drop for column header reorder

[6pac-ai]

Context

Part 2 of the SortableJS removal (port of slickgrid-universal's refactor(core)!: drop SortableJS dependency #2634). Stacked on #1240 — the characterization specs landed there pass unchanged against this new engine; that was the acceptance gate for this PR.

After this PR the grid itself no longer uses SortableJS for header column reordering. The SlickDraggableGrouping plugin still does (next PR), so the dependency and the example <script> tags stay for now.

What's in here

• src/slick.interactions.ts — new setupColumnReorderDrag(): native HTML5 drag & drop with live DOM reordering during dragover, browser-edge auto-scroll, a Firefox/Linux mouse-based fallback (native HTML5 drag is broken there), a touch fallback with a manual drag ghost (touch screens never fire HTML5 drag events), and dropzone hooks that the draggable-grouping port will use. Registered on the Slick namespace so iife/browser builds keep working with no new <script> tag (every example already loads slick.interactions.js).
• src/slick.grid.ts — sortablejs type imports and the two Sortable instances removed; setupColumnReorder() rewired onto the new engine with a column-map reconciliation in onDragEnd: hidden and reorderable: false columns keep their original indices. This fixes a latent bug — the old toArray() read-back silently dropped hidden columns from the grid on any reorder (hidden columns render no header, so the DOM read-back omitted them).
• src/models/interactions.interface.ts (+ColumnReorderDragOption), src/global.d.ts (Slick namespace typing), src/styles/slick.grid.scss (fallback drag-ghost rule).
• Cypress: the hidden-column characterization test from test(cypress): Replace SortableJS 1/4: characterize column header reorder ahead of SortableJS removal #1240 is un-skipped (it documents the fix above and now passes — it cannot pass on SortableJS), and a redundant spec-level @4tw/cypress-drag-drop import in example-grid-menu.cy.ts is removed (it re-registered the plugin's drag command over the shared HTML5 DnD overwrite from test(cypress): Replace SortableJS 1/4: characterize column header reorder ahead of SortableJS removal #1240).

Deliberate deviations from the upstream engine

Both preserve the previous SortableJS behavior that the #1240 characterization specs pin:

1. Frozen boundary stays uncrossable — reorders are constrained to the dragged column's own header container. Upstream's engine allows dragging a header across the left/right (frozen) boundary; SortableJS's two unconnected lists never did.
2. The drag finalizes on drop as well as dragend — SortableJS finalized on drop. Without this, drag sources that dispatch drop without a following dragend leave the header DOM visually reordered while setColumns()/onColumnsReordered never run.

Not in here

• dist/** is intentionally not rebuilt in this PR (release commits regenerate it).
• SortableJS stays in package.json and in the example pages until the DraggableGrouping port and the final removal sweep.

Verification

• Full 47-spec Cypress suite against the rebuilt bundles: 600/601 passing, 0 failures (1 intentional pending) — including all test(cypress): Replace SortableJS 1/4: characterize column header reorder ahead of SortableJS removal #1240 characterization specs unchanged: plain/frozen reorder, unorderable columns (blocked from moving, still resizable), onColumnsReordered payloads, scroll preservation, edge auto-scroll, cross-boundary lock, grouping pill drags and header→dropzone drop (still SortableJS-driven in the plugin).
• npm run lint and npm run build:types (strict TS) clean.
• dist/browser/slick.grid.js contains no SortableJS references after the change; the only remaining Sortable.create call sites in the bundles come from slick.draggablegrouping.ts.

Next up: port SlickDraggableGrouping off SortableJS (setupDropzonePillDrag), then remove the dependency and sweep the ~100 example pages.

🤖 Generated with Claude Code