feat(16.2-01): translatable plugin fields, element uploads and save notices in the admin

- MLPluginField wraps PluginField in the MLField locale switcher; the
  element gets the active content locale and that locale's string
- isMLField treats a translatable plugin field as a locale map in the form
  state, FormView adopt and the relation child modal
- summer-upload posts the file with the admin session to the field upload
  route and answers summer-upload-result {id, url} or {id, error}
- noticeLines shows meta.notices under each field as a warning status line
  (text only) and in the saved toast; the stored value is reloaded
- docs/backend/field-types.md documents the full element contract;
  modules/boardwalk/dist rebuilt

admin/src/views/FormView.vue

@@ -24,8 +24,9 @@ import {
   fieldErrors,
   focusField,
   initialValues,
-  isMLFieldType,
+  isMLField,
   mergeMLValue,
+  noticeLines,
   panelDomId,
   presetUpdates,
   recordDisplayName,
@@ -68,6 +69,9 @@ const errors = ref<Record<string, string[]>>({})
 // The text of a save the server refused with 403 (UI-SPEC S6). It is a
 // banner, not a toast: it stays readable until the next save attempt.
 const forbidden = ref<string | null>(null)
+// What plugin field types changed on the last save (meta.notices, D-10):
+// lines under each field until the next save attempt.
+const notices = ref<Record<string, string[]>>({})
 const loading = ref(true)
 const failed = ref(false)
 const busy = ref(false)
@@ -177,7 +181,7 @@ function adopt(record: RecordEnvelope | undefined): void {
     for (const field of fields.value) {
       if (field.type === 'password') {
         next[field.name] = ''
-      } else if (isMLFieldType(field.type)) {
+      } else if (isMLField(field)) {
         next[field.name] = mergeMLValue(record.data[field.name], locales)
       }
     }
@@ -248,8 +252,7 @@ function update(name: string, value: unknown): void {
   const previous = values.value[name]
   const next = { ...values.value, [name]: value }
   edited.add(name)
-  const type = fields.value.find((field) => field.name === name)?.type
-  if (isMLFieldType(type)) {
+  if (isMLField(fields.value.find((field) => field.name === name))) {
     let locales = editedLocales.get(name)
     if (!locales) {
       locales = new Set<string>()
@@ -319,6 +322,7 @@ async function save(): Promise<RecordEnvelope | null> {
   }
   busy.value = true
   forbidden.value = null
+  notices.value = {}
   try {
     const body = editablePayload(fields.value, values.value, mode)
     const result =
@@ -330,11 +334,18 @@ async function save(): Promise<RecordEnvelope | null> {
           })
     if (result.data) {
       errors.value = {}
+      // adopt reloads the stored values, so a field whose type changed the
+      // submitted value shows what was stored.
       adopt(result.data)
+      notices.value = noticeLines(result.data.meta.notices)
       // The save committed everything held against the session.
       pendingChanges.value = 0
       revision.value++
-      showToast(message(schema.value.messages.saved, undefined, { name: recordName.value }))
+      const savedText = message(schema.value.messages.saved, undefined, { name: recordName.value })
+      // The toast repeats the notices, so a save that navigates away (save
+      // and close) still tells the administrator what changed.
+      const noticeText = Object.values(notices.value).flat().join(' ')
+      showToast(noticeText === '' ? savedText : `${savedText} ${noticeText}`)
       return result.data
     }
     if (result.response.status === 422) {
@@ -502,6 +513,7 @@ void load()
           :fields="panelFields"
           :values="values"
           :errors="errors"
+          :notices="notices"
           :labels="labels"
           :source="path"
           :record-id="recordId"