Show only changed fields (delta) in ticket activity timeline

Before: entire ticket data was logged and shown in the activity tab.
After: compare old vs new values before saving; log only fields that
actually changed as { field: { from: '...', to: '...' } } pairs.

- TicketController.php: fetch old ticket before update, compute delta
- api/update_ticket.php: same fix for the API endpoint (currentTicket
  already fetched for auth, reuse it for delta comparison)
- TicketView.php: render delta format as "Field: old → new" with color;
  truncate long values (description) at 60 chars; keep legacy flat format
  as fallback for older log entries

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/update_ticket.php

@@ -180,9 +180,20 @@ try {
                 $this->ticketModel->updateVisibility($id, $data['visibility'], $visibilityGroups, $this->userId);
             }
 
-            // Log ticket update to audit log
+            // Log ticket update to audit log — only the changed fields (delta)
             if ($this->userId) {
-                $this->auditLog->logTicketUpdate($this->userId, $id, $data);
+                $trackFields = ['title', 'priority', 'status', 'description', 'category', 'type'];
+                $delta = [];
+                foreach ($trackFields as $field) {
+                    $oldVal = (string)($currentTicket[$field] ?? '');
+                    $newVal = (string)($updateData[$field] ?? '');
+                    if ($oldVal !== $newVal) {
+                        $delta[$field] = ['from' => $oldVal, 'to' => $newVal];
+                    }
+                }
+                if (!empty($delta)) {
+                    $this->auditLog->logTicketUpdate($this->userId, $id, $delta);
+                }
             }
 
             return [

controllers/TicketController.php

@@ -161,14 +161,28 @@ class TicketController {
                 return;
             }
 
+            // Fetch current ticket values before updating (for delta logging)
+            $oldTicket = $this->ticketModel->getTicketById((int)$id);
+
             // Update ticket with user tracking
             // Pass expected_updated_at for optimistic locking if provided
             $expectedUpdatedAt = $data['expected_updated_at'] ?? null;
             $result = $this->ticketModel->updateTicket($data, $userId, $expectedUpdatedAt);
 
-            // Log ticket update to audit log
-            if ($result['success'] && isset($GLOBALS['auditLog']) && $userId) {
-                $GLOBALS['auditLog']->logTicketUpdate($userId, $id, $data);
+            // Log ticket update to audit log — only the changed fields (delta)
+            if ($result['success'] && isset($GLOBALS['auditLog']) && $userId && $oldTicket) {
+                $trackFields = ['title', 'priority', 'status', 'description', 'category', 'type'];
+                $delta = [];
+                foreach ($trackFields as $field) {
+                    $oldVal = (string)($oldTicket[$field] ?? '');
+                    $newVal = (string)($data[$field] ?? '');
+                    if ($oldVal !== $newVal) {
+                        $delta[$field] = ['from' => $oldVal, 'to' => $newVal];
+                    }
+                }
+                if (!empty($delta)) {
+                    $GLOBALS['auditLog']->logTicketUpdate($userId, $id, $delta);
+                }
             }
 
             // Return JSON response

views/TicketView.php

@@ -569,11 +569,26 @@ include __DIR__ . '/layout_header.php';
                   if (is_array($det)) {
                       $parts = [];
                       foreach ($det as $k => $v) {
-                          if ($k !== 'old_value' && $k !== 'new_value') {
+                          // Delta format: { field: { from: '...', to: '...' } }
+                          if (is_array($v) && isset($v['from'], $v['to'])) {
+                              $label = ucfirst(str_replace('_', ' ', $k));
+                              // Truncate long values (e.g. description)
+                              $from = mb_strlen((string)$v['from']) > 60
+                                  ? mb_substr((string)$v['from'], 0, 60) . '…'
+                                  : (string)$v['from'];
+                              $to = mb_strlen((string)$v['to']) > 60
+                                  ? mb_substr((string)$v['to'], 0, 60) . '…'
+                                  : (string)$v['to'];
+                              $parts[] = '<strong>' . htmlspecialchars($label) . ':</strong> '
+                                  . '<span class="lt-text-muted">' . htmlspecialchars($from) . '</span>'
+                                  . ' <span class="lt-text-amber">→</span> '
+                                  . '<span class="lt-text-cyan">' . htmlspecialchars($to) . '</span>';
+                          } elseif ($k !== 'old_value' && $k !== 'new_value') {
+                              // Legacy flat format fallback
                               $parts[] = '<strong>' . htmlspecialchars($k) . ':</strong> ' . htmlspecialchars((string)$v);
                           }
                       }
-                      echo implode(', ', $parts);
+                      echo implode('<br>', $parts);
                   }
                   ?>
                 </div>