feat(template): stable fieldId per field — custom_fields keyed by UUID, not label slug

frontend/src/components/DailyStatusForm.jsx

@@ -7,11 +7,12 @@ import { dailyStatusesApi } from '../api/client';
 
 const BUILTIN_KEYS = new Set(['experiment_description', 'vitals', 'treatment', 'notes']);
 
-/** Extract the value for a field from a status record */
+/** Extract the value for a field from a status record.
+ *  Custom fields are keyed by fieldId (stable UUID), not by key (display slug). */
 function getValue(status, field) {
   if (!status) return '';
   if (field.builtin) return status[field.key] ?? '';
-  return status.custom_fields?.[field.key] ?? '';
+  return status.custom_fields?.[field.fieldId] ?? '';
 }
 
 export default function DailyStatusForm({ existing, animalId, template = [], onSuccess, onCancel }) {
@@ -63,12 +64,17 @@ export default function DailyStatusForm({ existing, animalId, template = [], onS
       const custom = {};
       for (const f of activeFields) {
         const val = values[f.key] || null;
-        if (f.builtin) builtin[f.key] = val;
-        else custom[f.key] = val;
+        if (f.builtin) {
+          builtin[f.key] = val;
+        } else {
+          // Always key by fieldId so renaming or recreating a field never
+          // collides with or orphans data from a different field.
+          custom[f.fieldId] = val;
+        }
       }
 
-      // Merge with any pre-existing custom_fields not in current active template
-      // (so we don't wipe data for fields that were hidden after the entry was made)
+      // Preserve custom_fields for fields not in the current active template
+      // (e.g. a field was hidden after this record was created).
       const existingCustom = existing?.custom_fields ?? {};
       const mergedCustom = { ...existingCustom, ...custom };
 

frontend/src/components/TemplateEditor.jsx

@@ -53,7 +53,14 @@ function FieldRow({ field, onChange, onToggle, onRemove, allKeys }) {
           onKeyDown={(e) => { if (e.key === 'Enter') { e.preventDefault(); commitLabel(); } }}
         />
         {labelError && <p className="text-xs text-red-500 mt-0.5">{labelError}</p>}
-        <p className="text-xs text-gray-400 mt-0.5 font-mono">key: {field.key}</p>
+        <p className="text-xs text-gray-400 mt-0.5 font-mono">
+          key: {field.key}
+          {field.fieldId && (
+            <span className="ml-2 text-gray-300" title={`Stable field ID: ${field.fieldId}`}>
+              · id: {field.fieldId.slice(0, 8)}…
+            </span>
+          )}
+        </p>
       </div>
 
       {/* Type badge */}
@@ -133,7 +140,8 @@ export default function TemplateEditor({ experimentId, onClose }) {
     if (!key) { setAddError('Name must contain at least one alphanumeric character'); return; }
     if (fields.some((f) => f.key === key)) { setAddError(`A field with key "${key}" already exists`); return; }
     setAddError('');
-    setFields((prev) => [...prev, { key, label: trimmed, type: newType, builtin: false, active: true }]);
+    const fieldId = crypto.randomUUID();
+    setFields((prev) => [...prev, { fieldId, key, label: trimmed, type: newType, builtin: false, active: true }]);
     setNewLabel('');
     setNewType('text');
   }

frontend/src/pages/AnimalDetail.jsx

@@ -9,10 +9,11 @@ import DailyStatusForm from '../components/DailyStatusForm';
 import Alert from '../components/ui/Alert';
 import AuditLogSection from '../components/AuditLogSection';
 
-/** Render the value for a template field from a status record */
+/** Read the value for a template field from a status record.
+ *  Custom fields are keyed by fieldId, not by the display key. */
 function getFieldValue(status, field) {
   if (field.builtin) return status[field.key];
-  return status.custom_fields?.[field.key];
+  return status.custom_fields?.[field.fieldId];
 }
 
 export default function AnimalDetail() {