fix(plugin-kanban): a lane that refuses the dragged card says why (#27133)

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_Requested by **Warren** · [project
thread](https://claude.ai/code/project/chan_01U5RdnAAmkSQmZbqh6FtqZ8?thread=cmsg_01U5RdnAAmkSQmZbqh6FtqZ8Va1s9AYECZKBfU5vttxtZo)_
Fixes #27099

## 维护者速读

- 改了什么:看板拖卡时,被状态机规则挡住的列除了变暗,还在 `title`(鼠标悬停提示)和
`aria-describedby`(读屏)里说明原因;泳道布局的格子同样。
- 为什么改:变暗的列不说为什么拒收,用户只会反复试或提工单;原因直接取自挡住这次移动的规则的
`message`,即服务端拒收同一移动时给出的那句话。
- 风险与回滚:只加属性和一个视觉隐藏的 span,开着的列与拖拽外一律不变;回滚即 revert 本 PR,无数据或元数据影响。
- 先看:`ui/packages/plugin-kanban/src/ObjectKanban.tsx` 的
`dropBlockedReason`,再看 `KanbanImpl.tsx` 的 `dropBlockedReasonFor`
与两处车道属性。
- 两分钟验证:`pnpm --dir ui exec vitest run
packages/plugin-kanban/src/ObjectKanban.dropBlockedReason-27099.test.tsx
packages/plugin-kanban/src/__tests__/dropBlockedReason-27099.test.tsx`,预期
8 个测试全绿。
- 需要你做的:无,席位落地。

Clause-②: no
Metadata-protocol: none

## What changes

- **`KanbanImpl.tsx`.** `KanbanBoardProps` gains an optional
`dropBlockedReason(fromColumnId, toColumnId)` beside `canDropCard`.
While a card is dragged, a lane the gate closes now carries the reason
as its `title` and as the text of a visually hidden span its
`aria-describedby` names. The swimlane layout's cells, which draw the
same three blocked attributes on their own, carry it the same way (one
id per row and column). An open lane, and every lane outside a drag,
carries neither. When the host gives no reason, the lane uses the new
pack sentence `kanban.dropBlocked` ("A card in {{from}} cannot be moved
to {{to}}.") with the two column titles.
- **`ObjectKanban.tsx`.** Supplies the reason: the `message` of each
blocking `state_machine` rule on the grouped field that refuses the
move. Each rule is asked alone through the gate's own read
(`stateMachineNextValues`), so a rule the gate ignores (warning-only,
inactive, insert-only, or silent on the card's value) is never named,
and no second copy of the gate's predicate exists. Several closing rules
join their messages; a blank message falls through to the board
sentence. `stateMachineNextValues` and `@object-ui/core` are untouched.
- **`KanbanBoardCore.tsx`.** Threads the new prop, as it does
`canDropCard`.
- **`@object-ui/i18n`.** `kanban.dropBlocked` in all ten packs.
- **Changeset.** `@object-ui/plugin-kanban` and `@object-ui/i18n`,
patch.

## Why

The card's Expected: a blocked lane exposes the reason the drop is
refused, worded from the rule that blocks it, through a title and
`aria-describedby` on the existing lane element, with no new widget.
Measured on `origin/main` before the change: the only supplier of the
gate is `ObjectKanban`'s `canDropCard`, and the only thing it reads is
the blocking `state_machine` rule on the `groupBy` field. A required
field never closes a lane (it prompts after the drop), and a missing
update grant makes the cards not movable, so no lane is dimmed for
either. The card's "transition, required field or permission" therefore
reduces to the state-machine rule, whose `message` the spec requires.

## Tests

- `ObjectKanban.dropBlockedReason-27099.test.tsx` (new, beside the
drop-gate test): the closed lane's `title` and accessible description
are the rule's message; CONTROL, an open lane and every lane before the
drag explain nothing; the reason leaves with the drag; two closing rules
are joined while a rule silent on the from-state and a warning-only rule
are not named; a blank message falls back to the board sentence.
- `__tests__/dropBlockedReason-27099.test.tsx` (new, real `DndContext`,
pointer pick-up): every swimlane row's closed cell carries the reason
and the open column's cells do not; the fallback is read from the zh
pack under a zh provider (the two packs are first shown to differ); a
host's `dropBlockedReason` wins over the fallback.

## Acceptance notes

- The reason is the text `/meta` serves. The server's refusal of the
same move resolves the message against
`objects.OBJECT._validations.RULE.message` in the caller's language, but
`translateObject` in `@objectstack/spec` (the served object's
translation) does not touch `validations[].message`, and nothing in
`ui/` reads that key. Under a translated locale the lane therefore shows
the authored text while the refusal toast would show the translated one.
Reported to the seat as a finding; not changed here.
- The fallback sentence names column titles, not values, so it reads the
same on every board.

## Verification

All runs at head `18f0af77` (the branch with `origin/main` `6817bf1e`
merged), except the two ablations, which ran on the pre-merge commit
`6dc7501f` carrying the same feature diff.

<details><summary>New and neighbouring tests</summary>

`pnpm --dir ui exec vitest run --maxWorkers=2` over the two new files
and `ObjectKanban.stateMachineDropGate-25933.test.tsx`: Test Files 3
passed (3), Tests 14 passed (14).

</details>

<details><summary>Ablations (each restored, blob equal to HEAD and `git
diff HEAD` empty, through `scripts/ablation-replace.mjs`)</summary>

- Deleting the flat lane's `title` and `aria-describedby` lines:
`ObjectKanban.dropBlockedReason-27099.test.tsx` 4 failed, 1 passed (the
CONTROL).
- Deleting the swimlane cell's `title` and `aria-describedby` lines:
`__tests__/dropBlockedReason-27099.test.tsx` 1 failed (the swimlane
case), 2 passed.

</details>

<details><summary>Package suites and type-check</summary>

- `pnpm --dir ui exec vitest run --maxWorkers=2 packages/plugin-kanban/
packages/i18n/`: Test Files 171 passed (171), Tests 1910 passed, 13
skipped.
- `pnpm --filter @object-ui/plugin-kanban --filter @object-ui/i18n run
type-check`: exit 0 for both.

</details>

<details><summary>Derived gates</summary>

`node scripts/pm/dispatch-gates.mjs --commands --repo
objectstack-ai/objectstack` derived 34 commands; all 34 ran and exited 0
(exit captured before any pipe), plus `pnpm check:changeset-fixed` and
`pnpm --dir ui run check:new-line-citations` outside the derivation,
both exit 0. `--ran` reconciliation: 34 derived, 34 run, 0 NOT-MEASURED,
0 UNRUN. Families CI runs beyond the derivation (lint, type-check lanes,
the full UI shards) are left to this PR's check-runs.

</details>

## Human Minimum

- [x] 1. Schemas start as Zod; `packages/spec` holds no runtime logic.
- [x] 2. Every name I added uses the casing for its kind.
- [x] 3. No formatter ran; `pnpm lint` passes. (No formatter ran; `pnpm
lint` is CI's run.)
- [x] 4. One issue, one branch off an up-to-date `main`, one pull
request.
- [x] 5. A change that publishes carries a changeset, and both
declaration lines are filled in here and in the changeset.
- [x] 6. `packages/spec` touched: its generated artifacts are
regenerated and committed. (Not touched.)
- [x] 7. No hand edits to `content/docs/references/`,
`packages/*/CHANGELOG.md` or `content/docs/releases/`.
- [x] 8. Title, body and comments are in English. (The 维护者速读 block is
the dispatch order's required Chinese section.)
- [x] The *Before Submitting* list in CONTRIBUTING.md is done.

---
_Generated by [Claude
Code](https://claude.ai/code/session_01JQwxbZzYH3oXtLp9fbSkzn)_

Co-authored-by: Claude <noreply@anthropic.com>

Author: objectstack-fleet[bot]

.changeset/27099-kanban-blocked-lane-reason.md

@@ -0,0 +1,14 @@
+---
+'@object-ui/plugin-kanban': patch
+'@object-ui/i18n': patch
+---
+
+fix(plugin-kanban): a lane that refuses the dragged card now says why
+
+Clause-②: no
+Metadata-protocol: none
+
+While a card is dragged, a lane the board's drop gate closes was dimmed and `aria-disabled` with nothing saying why. It now carries the reason as its `title` (a pointer user's tooltip) and as the text its `aria-describedby` names (assistive tech). An open lane carries neither, and the reason leaves with the drag. The swimlane layout's cells carry it the same way.
+
+- **`object-kanban`.** The reason is the `message` of each blocking `state_machine` rule on the grouped field that refuses the move, the sentence the server's refusal of the same move carries. A rule the gate ignores (warning-only, inactive, insert-only, or silent on the card's value) is never named; several closing rules join their messages.
+- **Hosts of the board.** `KanbanBoardProps` gains an optional `dropBlockedReason(fromColumnId, toColumnId)` beside `canDropCard`. A host that answers nothing, or passes no function, gets the new `kanban.dropBlocked` sentence ("A card in To Do cannot be moved to Done.") with the two column titles, in all ten language packs.

ui/packages/i18n/src/locales/ar.ts

@@ -986,6 +986,7 @@ const ar = {
     noCards: "لا بطاقات",
     columnCards: "بطاقات العمود {{column}}",
     laneCards: "بطاقات {{column}} - {{lane}}",
+    dropBlocked: "لا يمكن نقل بطاقة من {{from}} إلى {{to}}.",
     cardTitlePlaceholder: "أدخل عنوان البطاقة…",
     requiredFieldsTitle: "أكمل الحقول المطلوبة",
     requiredFieldsDescription: "يجعل هذا النقل الحقول أدناه مطلوبة. أكملها للمتابعة.",

ui/packages/i18n/src/locales/de.ts

@@ -881,6 +881,7 @@ const de = {
     noCards: "Keine Karten",
     columnCards: "Karten in Spalte {{column}}",
     laneCards: "Karten in {{column}} - {{lane}}",
+    dropBlocked: "Eine Karte aus {{from}} kann nicht nach {{to}} verschoben werden.",
     cardTitlePlaceholder: "Kartentitel eingeben…",
     requiredFieldsTitle: "Erforderliche Felder ausfüllen",
     requiredFieldsDescription: "Durch diese Verschiebung werden die folgenden Felder zu Pflichtfeldern. Füllen Sie sie aus, um fortzufahren.",

ui/packages/i18n/src/locales/en.ts

@@ -1137,6 +1137,7 @@ const en = {
     noCards: 'No cards',
     columnCards: '{{column}} cards',
     laneCards: '{{column}} - {{lane}} cards',
+    dropBlocked: 'A card in {{from}} cannot be moved to {{to}}.',
     cardTitlePlaceholder: 'Enter card title…',
     uncategorized: 'Uncategorized',
     loadMore: 'Load more',

ui/packages/i18n/src/locales/es.ts

@@ -910,6 +910,7 @@ const es = {
     noCards: "Sin tarjetas",
     columnCards: "Tarjetas de la columna {{column}}",
     laneCards: "Tarjetas de {{column}} - {{lane}}",
+    dropBlocked: "Una tarjeta de {{from}} no se puede mover a {{to}}.",
     cardTitlePlaceholder: "Escriba el título de la tarjeta…",
     requiredFieldsTitle: "Complete los campos obligatorios",
     requiredFieldsDescription: "Este movimiento hace que los campos siguientes sean obligatorios. Complételos para continuar.",

ui/packages/i18n/src/locales/fr.ts

@@ -905,6 +905,7 @@ const fr = {
     noCards: "Aucune carte",
     columnCards: "Cartes de la colonne {{column}}",
     laneCards: "Cartes de {{column}} - {{lane}}",
+    dropBlocked: "Une carte de {{from}} ne peut pas être déplacée vers {{to}}.",
     cardTitlePlaceholder: "Saisir le titre de la carte…",
     requiredFieldsTitle: "Compléter les champs obligatoires",
     requiredFieldsDescription: "Ce déplacement rend les champs ci-dessous obligatoires. Remplissez-les pour continuer.",

ui/packages/i18n/src/locales/ja.ts

@@ -881,6 +881,7 @@ const ja = {
     noCards: "カードがありません",
     columnCards: "{{column}} のカード",
     laneCards: "{{column}} - {{lane}} のカード",
+    dropBlocked: "{{from}} のカードは {{to}} に移動できません。",
     cardTitlePlaceholder: "カードのタイトルを入力…",
     requiredFieldsTitle: "必須項目を入力してください",
     requiredFieldsDescription: "この移動により以下の項目が必須になります。入力して続行してください。",

ui/packages/i18n/src/locales/ko.ts

@@ -881,6 +881,7 @@ const ko = {
     noCards: "카드 없음",
     columnCards: "{{column}} 열의 카드",
     laneCards: "{{column}} - {{lane}}의 카드",
+    dropBlocked: "{{from}}의 카드는 {{to}}에 놓을 수 없습니다.",
     cardTitlePlaceholder: "카드 제목 입력…",
     requiredFieldsTitle: "필수 항목 입력",
     requiredFieldsDescription: "이 이동으로 아래 항목이 필수가 됩니다. 입력한 후 계속하세요.",

ui/packages/i18n/src/locales/pt.ts

@@ -905,6 +905,7 @@ const pt = {
     noCards: "Sem cartões",
     columnCards: "Cartões da coluna {{column}}",
     laneCards: "Cartões de {{column}} - {{lane}}",
+    dropBlocked: "Um cartão em {{from}} não pode ser movido para {{to}}.",
     cardTitlePlaceholder: "Digite o título do cartão…",
     requiredFieldsTitle: "Preencha os campos obrigatórios",
     requiredFieldsDescription: "Esta movimentação torna os campos abaixo obrigatórios. Preencha-os para continuar.",

ui/packages/i18n/src/locales/ru.ts

@@ -935,6 +935,7 @@ const ru = {
     noCards: "Нет карточек",
     columnCards: "Карточки в колонке {{column}}",
     laneCards: "Карточки: {{column}} - {{lane}}",
+    dropBlocked: "Карточку из {{from}} нельзя переместить в {{to}}.",
     cardTitlePlaceholder: "Введите название карточки…",
     requiredFieldsTitle: "Заполните обязательные поля",
     requiredFieldsDescription: "Это перемещение делает поля ниже обязательными. Заполните их, чтобы продолжить.",