Make a partly-undone import retryable, and refuse a plan it cannot deliver

frontend/src/views/settings/ImportSiteAssets.vue

@@ -269,7 +269,7 @@
               below if needed.
             </template>
             <template v-else-if="wincReport.blocking">
-              {{ wincReport.rowcount }} row(s) in scope, but unresolved values
+              {{ wincReport.rowcount }} row(s) in scope, but the problems below
               block the import - nothing was written. Resolve them and preview
               again.
             </template>
@@ -314,6 +314,29 @@
             </label>
           </div>
 
+          <!-- Blocking and NOT acknowledgeable, unlike needscreate above.
+               The packet blocks on these, so the page must name them or the
+               banner points at nothing the admin can see. -->
+          <div
+            v-if="wincReport.uncreatable && Object.keys(wincReport.uncreatable).length"
+            class="problems"
+          >
+            <h4>Rows this import cannot create (blocking)</h4>
+            <p class="muted">
+              The export needs these, but this import only ever creates business
+              units. Create them in Settings first, or alias the export values
+              to rows that already exist, then preview again.
+            </p>
+            <ul>
+              <li v-for="(items, group) in wincReport.uncreatable" :key="group">
+                <strong>{{ group }}:</strong>
+                <span v-for="(count, name) in items" :key="name">
+                  "{{ name }}" ({{ count }}){{ ' ' }}
+                </span>
+              </li>
+            </ul>
+          </div>
+
           <div v-if="wincReport.unresolved && Object.keys(wincReport.unresolved).length" class="problems">
             <h4>Unresolved values (blocking)</h4>
             <p class="muted">
@@ -354,15 +377,27 @@
                 <td>{{ b.createdat }}</td>
                 <td>{{ b.createdby || '-' }}</td>
                 <td>{{ b.rowcount }}</td>
-                <td>{{ b.status }}</td>
                 <td>
+                  {{ b.status }}
+                  <small v-if="b.status === 'partially-undone'" class="muted">
+                    - some rows could not be put back
+                  </small>
+                </td>
+                <td>
+                  <!-- 'partially-undone' is retryable and MUST offer the
+                       button: that status exists because an undo stopped at a
+                       conflict, and retrying once the conflict is resolved is
+                       the whole point. Testing only for 'applied' left the
+                       backend willing and the button hidden. -->
                   <button
-                    v-if="b.status === 'applied'"
+                    v-if="b.status === 'applied' || b.status === 'partially-undone'"
                     class="btn btn-secondary btn-sm"
                     :disabled="wincUndoingId === b.batchid"
                     @click="undoWincBatch(b.batchid)"
                   >
-                    {{ wincUndoingId === b.batchid ? 'Undoing...' : 'Undo' }}
+                    {{ wincUndoingId === b.batchid
+                        ? 'Undoing...'
+                        : (b.status === 'partially-undone' ? 'Retry undo' : 'Undo') }}
                   </button>
                   <span v-else class="muted">undone</span>
                 </td>