chore(ui): changeset for the board's state-machine drop gate

Claude-Session: https://claude.ai/code/session_015Kzn5VKHAGKe251waHoUqj
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

.changeset/25933-state-machine-board-drop-gate.md

@@ -0,0 +1,15 @@
+---
+'@object-ui/plugin-kanban': patch
+---
+
+feat(plugin-kanban): the board dims the lanes a dragged card's `state_machine` closes and refuses a drop into one
+
+Clause-②: yes
+Metadata-protocol: none
+
+A board grouped by a field that an error-severity `state_machine` validation governs (the showcase Task Board's `status`, for one) used to accept a card dragged onto any column. The server refused the invalid move and the board rolled it back with a toast, and nothing during the drag marked the columns the card could not enter.
+
+- **While a card is dragged**, every lane its column's value may not move to is dimmed and draws no drop highlight (`aria-disabled`, `data-kanban-drop-blocked`), on the flat layout and in every swimlane row.
+- **A drop into such a lane is refused on the client**, before the optimistic move and before any write: the card stays in its column. A cancelled drag puts the lanes back.
+- **Which lanes close** is read through `stateMachineNextValues` from `@object-ui/core`, the same read the record form and the grid's inline editor use. Only a rule on the board's own `groupBy` field that the server enforces on update closes a lane (`severity` `error`, `active`, `events` covering `update`). An undeclared from-state and the Uncategorized lane stay open.
+- `KanbanBoard` (the lazily loaded board both entry points render) takes a new optional prop, `canDropCard(fromColumnId, toColumnId)`. `ObjectKanban` derives it; `KanbanRenderer` passes none, so a host-mounted board is unchanged. The server still refuses an invalid move, and the mover's rollback stays. No new visible text.