refactor(task-modal): enhance employee timeblock management with custom filtering and improved rendering logic

app/src/plugins/tm@modal/task/z-task-modal.vue

@@ -102,7 +102,7 @@
             :timeblocks="getEmployeeTimeblocks(subtask.employee_id)"
             :all-timeblocks="timeblocks"
             :deleted-timeblock-ids="deletedTimeblockIds"
-            :custom-filter="customFilter"
+            :custom-filter="getEmployeeCustomFilter(subtask.employee_id)"
             @update:timeblocks="
               updateEmployeeTimeblocks($event, subtask.employee_id)
             "
@@ -122,7 +122,7 @@
               :timeblocks="getEmployeeTimeblocks(employee.id)"
               :all-timeblocks="timeblocks"
               :deleted-timeblock-ids="deletedTimeblockIds"
-              :custom-filter="customFilter"
+              :custom-filter="getEmployeeCustomFilter(employee.id)"
               :required="index === 0"
               @update:timeblocks="updateEmployeeTimeblocks($event, employee.id)"
               @clear-employee="() => removeEmployeeAtIndex(index)"
@@ -564,6 +564,45 @@ export default {
       return this.timeblocks.filter((tb) => tb.employee_id == employeeId);
     },
 
+    // Custom filter for employee select to prevent selecting the same employee twice
+    // currentEmployeeId: the ID of the employee currently selected in this dropdown (can be null)
+    getEmployeeCustomFilter(currentEmployeeId) {
+      return (itemText, queryText, item) => {
+        // Get all selected employee IDs except the current one
+        const selectedEmployeeIds = new Set();
+
+        if (this.isDraftWithMultipleEmployees && this.subtask?.employees) {
+          // In multi-employee mode, collect all selected employee IDs except current
+          this.subtask.employees.forEach((emp) => {
+            if (emp.id && emp.id !== currentEmployeeId) {
+              selectedEmployeeIds.add(emp.id);
+            }
+          });
+        } else if (
+          this.subtask?.employee_id &&
+          this.subtask.employee_id !== currentEmployeeId
+        ) {
+          // In single employee edit mode
+          selectedEmployeeIds.add(this.subtask.employee_id);
+        }
+
+        // Filter out already selected employees (but allow current selection)
+        if (selectedEmployeeIds.has(item.id)) {
+          return false;
+        }
+
+        // Apply default text filtering (from AutocompleteMixin)
+        if (this.customFilter) {
+          return this.customFilter(itemText, queryText, item);
+        }
+
+        // Default case-insensitive text match
+        const searchText = queryText.toString().toLowerCase();
+        const text = itemText.toString().toLowerCase();
+        return text.indexOf(searchText) > -1;
+      };
+    },
+
     updateEmployeeTimeblocks(updatedTimeblocks, employeeId) {
       // Track deleted timeblocks (saved timeblocks that are no longer in the updated list)
       const updatedIds = new Set(