Fix what the last round of device fixes broke, and two dips it missed

plugins/network/frontend/views/NetworkDeviceForm.vue

@@ -24,9 +24,18 @@
                 type="text"
                 class="form-control"
                 :required="isEdit"
-                :disabled="isEdit"
+                :disabled="isEdit && !assetNumberMissing"
                 :placeholder="generatedAssetNumber || 'leave blank to generate from the name'"
               />
+              <!-- Locked while editing, because an asset number is identity and
+                   changing it silently re-keys the record. The exception is a
+                   record that HAS no number: those exist (an update path used to
+                   accept a blank), the server now rejects a blank on save, and
+                   with the field disabled there was no way to supply one - the
+                   row could not be saved at all until it was fixed elsewhere. -->
+              <small class="form-hint" v-if="assetNumberMissing">
+                This device has no asset number. Give it one to save.
+              </small>
               <small class="form-hint" v-if="!isEdit && !form.assetnumber && generatedAssetNumber">
                 Will be created as <code>{{ generatedAssetNumber }}</code>
               </small>
@@ -393,6 +402,10 @@ const generatedAssetNumber = computed(() => {
   if (name.toUpperCase().startsWith(prefix + '-')) return name
   return `${prefix}-${name}`
 })
+// True when the record loaded WITHOUT an asset number, which unlocks the field
+// so it can be repaired. Captured at load: once typed, the field must stay open.
+const assetNumberMissing = ref(false)
+
 const vendors = ref([])
 const models = ref([])
 
@@ -480,6 +493,9 @@ async function loadDevice() {
 
     // Populate form with existing data
     form.value.assetnumber = data.assetnumber || ''
+    // Remember that it arrived empty, so the field stays editable while the
+    // user types the number this record should have had.
+    assetNumberMissing.value = !(data.assetnumber || '').trim()
     form.value.name = data.name || ''
     form.value.serialnumber = data.serialnumber || ''
     form.value.gaugelabreference = data.gaugelabreference || ''