feat(bases): card-to-card kanban drag with edge slotting

apps/client/src/features/base/components/views/kanban/base-kanban.tsx

@@ -1,4 +1,4 @@
-import { useMemo } from "react";
+import { useCallback, useMemo } from "react";
 import {
   IBase,
   IBaseRow,
@@ -7,7 +7,15 @@ import {
 } from "@/features/base/types/base.types";
 import { useKanbanGroups } from "@/features/base/hooks/use-kanban-groups";
 import { useUpdateViewMutation } from "@/features/base/queries/base-view-query";
-import { useCreateRowMutation } from "@/features/base/queries/base-row-query";
+import {
+  useCreateRowMutation,
+  useReorderRowMutation,
+  useUpdateRowMutation,
+} from "@/features/base/queries/base-row-query";
+import { resolveCardDrop } from "@/features/base/hooks/resolve-card-drop";
+import type { CardDropPayload } from "@/features/base/hooks/use-kanban-card-drag";
+import { triggerPostMoveFlash } from "@atlaskit/pragmatic-drag-and-drop-flourish/trigger-post-move-flash";
+import * as liveRegion from "@atlaskit/pragmatic-drag-and-drop-live-region";
 import { KanbanColumn } from "./kanban-column";
 import { KanbanEmptyState } from "./kanban-empty-state";
 import classes from "@/features/base/styles/kanban.module.css";
@@ -40,6 +48,9 @@ export function BaseKanban({
   const isGroupable = property?.type === "select" || property?.type === "status";
   const updateViewMutation = useUpdateViewMutation();
   const createRowMutation = useCreateRowMutation();
+  const updateRowMutation = useUpdateRowMutation();
+  const reorderRowMutation = useReorderRowMutation();
+  const sortsActive = (effectiveView?.config?.sorts?.length ?? 0) > 0;
 
   // Rules of Hooks: call useKanbanGroups unconditionally with `undefined`
   // when not groupable; switch the render path on isGroupable below.
@@ -59,6 +70,60 @@ export function BaseKanban({
     });
   };
 
+  const handleCardDrop = useCallback(
+    (payload: CardDropPayload) => {
+      if (!groupByPropertyId) return;
+      const targetColumn = columns.find((c) => c.key === payload.targetColumnKey);
+      // The drop target restricts allowedEdges to ["top","bottom"], so the
+      // runtime value is always assignable; narrow the broader Edge union.
+      const edge =
+        payload.edge === "top" || payload.edge === "bottom"
+          ? payload.edge
+          : null;
+      const result = resolveCardDrop({
+        draggedCardId: payload.draggedCardId,
+        targetCardId: payload.targetCardId,
+        edge,
+        sourceColumnKey: payload.sourceColumnKey,
+        targetColumnKey: payload.targetColumnKey,
+        groupByPropertyId,
+        columnRows: targetColumn?.rows ?? [],
+        sortsActive,
+      });
+
+      if (result.cells !== undefined) {
+        updateRowMutation.mutate({
+          rowId: payload.draggedCardId,
+          pageId: base.id,
+          cells: result.cells,
+          ...(result.position !== undefined && { position: result.position }),
+        });
+      } else if (result.position !== undefined) {
+        reorderRowMutation.mutate({
+          rowId: payload.draggedCardId,
+          pageId: base.id,
+          position: result.position,
+        });
+      }
+
+      // a11y + post-move flash on the dropped card (if still in DOM).
+      const el = document.querySelector(
+        `[data-row-id="${payload.draggedCardId}"]`,
+      );
+      if (el instanceof HTMLElement) triggerPostMoveFlash(el);
+      const colName = targetColumn?.name ?? "column";
+      liveRegion.announce(`Moved card to ${colName}`);
+    },
+    [
+      base.id,
+      columns,
+      groupByPropertyId,
+      reorderRowMutation,
+      sortsActive,
+      updateRowMutation,
+    ],
+  );
+
   const handleAddCard = (columnKey: string) => {
     if (!groupByPropertyId) return;
     const cells =
@@ -87,6 +152,7 @@ export function BaseKanban({
           primaryProperty={primaryProperty}
           onCardClick={onCardClick}
           onAddCard={handleAddCard}
+          onCardDrop={handleCardDrop}
         />
       ))}
     </div>

apps/client/src/features/base/components/views/kanban/kanban-card.tsx

@@ -2,25 +2,46 @@ import { IBaseProperty, IBaseRow } from "@/features/base/types/base.types";
 import classes from "@/features/base/styles/kanban.module.css";
 import { useTranslation } from "react-i18next";
 import clsx from "clsx";
+import {
+  useKanbanCardDrag,
+  type CardDropPayload,
+} from "@/features/base/hooks/use-kanban-card-drag";
+import { BaseDropEdgeIndicator } from "@/features/base/components/grid/base-drop-edge-indicator";
 
 type KanbanCardProps = {
   row: IBaseRow;
+  columnKey: string;
   primaryProperty: IBaseProperty | undefined;
   onClick: (rowId: string) => void;
+  onDrop: (payload: CardDropPayload) => void;
 };
 
-export function KanbanCard({ row, primaryProperty, onClick }: KanbanCardProps) {
+export function KanbanCard({
+  row,
+  columnKey,
+  primaryProperty,
+  onClick,
+  onDrop,
+}: KanbanCardProps) {
   const { t } = useTranslation();
-  const titleValue =
-    primaryProperty
-      ? ((row.cells ?? {})[primaryProperty.id] as string | undefined)
-      : undefined;
+  const { ref, isDragging, closestEdge } = useKanbanCardDrag({
+    cardId: row.id,
+    columnKey,
+    onDrop,
+  });
+
+  const titleValue = primaryProperty
+    ? ((row.cells ?? {})[primaryProperty.id] as string | undefined)
+    : undefined;
   const titleText = titleValue?.trim().length ? titleValue : t("Untitled");
   const isEmpty = !titleValue?.trim().length;
 
   return (
     <div
+      ref={ref}
       className={classes.card}
+      data-row-id={row.id}
+      data-dragging={isDragging || undefined}
       role="button"
       tabIndex={0}
       onClick={() => onClick(row.id)}
@@ -34,6 +55,7 @@ export function KanbanCard({ row, primaryProperty, onClick }: KanbanCardProps) {
       <div className={clsx(classes.cardTitle, isEmpty && classes.cardTitleEmpty)}>
         {titleText}
       </div>
+      {closestEdge && <BaseDropEdgeIndicator edge={closestEdge} />}
     </div>
   );
 }

apps/client/src/features/base/components/views/kanban/kanban-column.tsx

@@ -3,6 +3,7 @@ import { IBaseProperty } from "@/features/base/types/base.types";
 import { KanbanCard } from "./kanban-card";
 import { KanbanColumnHeader } from "./kanban-column-header";
 import { KanbanAddCardButton } from "./kanban-add-card-button";
+import type { CardDropPayload } from "@/features/base/hooks/use-kanban-card-drag";
 import classes from "@/features/base/styles/kanban.module.css";
 
 type KanbanColumnProps = {
@@ -10,6 +11,7 @@ type KanbanColumnProps = {
   primaryProperty: IBaseProperty | undefined;
   onCardClick: (rowId: string) => void;
   onAddCard: (columnKey: string) => void;
+  onCardDrop: (payload: CardDropPayload) => void;
 };
 
 export function KanbanColumn({
@@ -17,6 +19,7 @@ export function KanbanColumn({
   primaryProperty,
   onCardClick,
   onAddCard,
+  onCardDrop,
 }: KanbanColumnProps) {
   return (
     <div className={classes.column} data-column-key={column.key}>
@@ -30,8 +33,10 @@ export function KanbanColumn({
           <KanbanCard
             key={row.id}
             row={row}
+            columnKey={column.key}
             primaryProperty={primaryProperty}
             onClick={onCardClick}
+            onDrop={onCardDrop}
           />
         ))}
         <KanbanAddCardButton onClick={() => onAddCard(column.key)} />

apps/client/src/features/base/hooks/use-kanban-card-drag.ts

@@ -0,0 +1,91 @@
+import { useEffect, useRef, useState } from "react";
+import { combine } from "@atlaskit/pragmatic-drag-and-drop/combine";
+import {
+  draggable,
+  dropTargetForElements,
+} from "@atlaskit/pragmatic-drag-and-drop/element/adapter";
+import {
+  attachClosestEdge,
+  extractClosestEdge,
+  type Edge,
+} from "@atlaskit/pragmatic-drag-and-drop-hitbox/closest-edge";
+
+export type CardDragData = {
+  type: "base-kanban-card";
+  cardId: string;
+  columnKey: string;
+};
+
+export type CardDropPayload = {
+  draggedCardId: string;
+  targetCardId: string;
+  edge: Edge;
+  sourceColumnKey: string;
+  targetColumnKey: string;
+};
+
+export function useKanbanCardDrag({
+  cardId,
+  columnKey,
+  onDrop,
+  disabled,
+}: {
+  cardId: string;
+  columnKey: string;
+  onDrop: (payload: CardDropPayload) => void;
+  disabled?: boolean;
+}) {
+  const ref = useRef<HTMLDivElement>(null);
+  const [isDragging, setIsDragging] = useState(false);
+  const [closestEdge, setClosestEdge] = useState<Edge | null>(null);
+  // Keep onDrop fresh without re-registering the effect each render.
+  const onDropRef = useRef(onDrop);
+  onDropRef.current = onDrop;
+
+  useEffect(() => {
+    const el = ref.current;
+    if (!el || disabled) return;
+    const data: CardDragData = {
+      type: "base-kanban-card",
+      cardId,
+      columnKey,
+    };
+    return combine(
+      draggable({
+        element: el,
+        getInitialData: () => data,
+        onDragStart: () => setIsDragging(true),
+        onDrop: () => setIsDragging(false),
+      }),
+      dropTargetForElements({
+        element: el,
+        canDrop: ({ source }) => {
+          if (source.data.type !== "base-kanban-card") return false;
+          return source.data.cardId !== cardId;
+        },
+        getData: ({ input, element }) =>
+          attachClosestEdge(
+            { type: "base-kanban-card-target", cardId, columnKey },
+            { input, element, allowedEdges: ["top", "bottom"] },
+          ),
+        onDrag: ({ self }) => setClosestEdge(extractClosestEdge(self.data)),
+        onDragLeave: () => setClosestEdge(null),
+        onDrop: ({ source, self }) => {
+          setClosestEdge(null);
+          if (source.data.type !== "base-kanban-card") return;
+          const edge = extractClosestEdge(self.data);
+          if (!edge) return;
+          onDropRef.current({
+            draggedCardId: source.data.cardId as string,
+            targetCardId: cardId,
+            edge,
+            sourceColumnKey: source.data.columnKey as string,
+            targetColumnKey: columnKey,
+          });
+        },
+      }),
+    );
+  }, [cardId, columnKey, disabled]);
+
+  return { ref, isDragging, closestEdge };
+}