diff --git a/client/src/components/Todo/TodoListPanel.tsx b/client/src/components/Todo/TodoListPanel.tsx
index 23c7b6082..482a14e9a 100644
--- a/client/src/components/Todo/TodoListPanel.tsx
+++ b/client/src/components/Todo/TodoListPanel.tsx
@@ -350,7 +350,7 @@ function DetailPane({ item, tripId, categories, members, onClose }: {
         name: name.trim(), description: desc || null,
         due_date: dueDate || null, category: category || null,
         assigned_user_id: assignedUserId, priority,
-      } as any)
+      })
     } catch (err: unknown) { toast.error(err instanceof Error ? err.message : t('common.error')) }
     setSaving(false)
   }
@@ -566,7 +566,7 @@ function NewTaskPane({ tripId, categories, members, defaultCategory, onCreated,
         name: name.trim(), description: desc || null, priority,
         due_date: dueDate || null, category: trimmedCategory || null,
         assigned_user_id: assignedUserId,
-      } as any)
+      })
       if (item?.id) onCreated(item.id)
     } catch (err: unknown) { toast.error(err instanceof Error ? err.message : t('common.error')) }
     setSaving(false)
diff --git a/client/src/mobile/screens/trip/tabs/MTaskSheet.tsx b/client/src/mobile/screens/trip/tabs/MTaskSheet.tsx
index a6e552d03..1f5e24b8b 100644
--- a/client/src/mobile/screens/trip/tabs/MTaskSheet.tsx
+++ b/client/src/mobile/screens/trip/tabs/MTaskSheet.tsx
@@ -20,19 +20,6 @@ export interface MTaskSheetProps {
   onClose: () => void
 }
 
-/** Payload shape covering both create and update — the update schema allows
- * clearing a field with `null`, which `TodoUpdateItemRequest` itself (typed
- * against the create request) doesn't express; the store call below is cast
- * to it rather than widened to `any`. */
-interface TodoSavePayload {
-  name: string
-  description: string | null
-  due_date: string | null
-  category: string | null
-  assigned_user_id: number | null
-  priority: number
-}
-
 /**
  * Add/Edit task sheet (spec 03 §4.7 `openTask` / progress-card "New task"):
  * name, description, list (category), due date, assignee and priority.
@@ -99,7 +86,7 @@ export default function MTaskSheet({ planner, open, itemId, categories, members,
     setSaving(true)
     try {
       if (item) {
-        const payload: TodoSavePayload = {
+        const payload: TodoUpdateItemRequest = {
           name: trimmedName,
           description: description || null,
           due_date: dueDate || null,
@@ -107,7 +94,7 @@ export default function MTaskSheet({ planner, open, itemId, categories, members,
           assigned_user_id: assignedUserId,
           priority,
         }
-        await tripActions.updateTodoItem(tripId, item.id, payload as unknown as TodoUpdateItemRequest)
+        await tripActions.updateTodoItem(tripId, item.id, payload)
       } else {
         const payload: TodoCreateItemRequest = {
           name: trimmedName,
diff --git a/shared/src/todo/todo.schema.spec.ts b/shared/src/todo/todo.schema.spec.ts
index ffb401d22..86143cf3a 100644
--- a/shared/src/todo/todo.schema.spec.ts
+++ b/shared/src/todo/todo.schema.spec.ts
@@ -17,6 +17,18 @@ describe('todoCreateItemRequestSchema', () => {
     // priority is numeric (matches the service), not a string
     expect(todoCreateItemRequestSchema.safeParse({ name: 'X', priority: 'high' }).success).toBe(false);
   });
+
+  it('accepts explicit null on the optional metadata fields (client clears with null)', () => {
+    expect(
+      todoCreateItemRequestSchema.safeParse({
+        name: 'X',
+        category: null,
+        due_date: null,
+        description: null,
+        assigned_user_id: null,
+      }).success,
+    ).toBe(true);
+  });
 });
 
 describe('todoUpdateItemRequestSchema', () => {
@@ -24,6 +36,25 @@ describe('todoUpdateItemRequestSchema', () => {
     expect(todoUpdateItemRequestSchema.safeParse({}).success).toBe(true);
     expect(todoUpdateItemRequestSchema.safeParse({ checked: true }).success).toBe(true);
   });
+
+  it('accepts checked as 0/1 (legacy numeric form) but rejects other numbers', () => {
+    expect(todoUpdateItemRequestSchema.safeParse({ checked: 1 }).success).toBe(true);
+    expect(todoUpdateItemRequestSchema.safeParse({ checked: 0 }).success).toBe(true);
+    expect(todoUpdateItemRequestSchema.safeParse({ checked: 2 }).success).toBe(false);
+  });
+
+  it('accepts explicit null on the nullable fields (bodyKeys clear protocol)', () => {
+    expect(
+      todoUpdateItemRequestSchema.safeParse({
+        category: null,
+        due_date: null,
+        description: null,
+        assigned_user_id: null,
+        priority: null,
+      }).success,
+    ).toBe(true);
+    expect(todoUpdateItemRequestSchema.safeParse({ name: null }).success).toBe(false);
+  });
 });
 
 describe('todoReorderRequestSchema', () => {
diff --git a/shared/src/todo/todo.schema.ts b/shared/src/todo/todo.schema.ts
index 2519adb75..e8e68bad0 100644
--- a/shared/src/todo/todo.schema.ts
+++ b/shared/src/todo/todo.schema.ts
@@ -12,22 +12,27 @@ import { z } from 'zod';
 
 export const todoCreateItemRequestSchema = z.object({
   name: z.string().min(1),
-  category: z.string().optional(),
-  due_date: z.string().optional(),
-  description: z.string().optional(),
-  assigned_user_id: z.number().optional(),
+  // The client clears optional fields by sending explicit null (the service
+  // coerces falsy to its defaults), so every optional metadata field is nullable.
+  category: z.string().nullable().optional(),
+  due_date: z.string().nullable().optional(),
+  description: z.string().nullable().optional(),
+  assigned_user_id: z.number().nullable().optional(),
   priority: z.number().optional(),
 });
 export type TodoCreateItemRequest = z.infer<typeof todoCreateItemRequestSchema>;
 
 export const todoUpdateItemRequestSchema = z.object({
   name: z.string().optional(),
-  checked: z.boolean().optional(),
-  category: z.string().optional(),
-  due_date: z.string().optional(),
-  description: z.string().optional(),
-  assigned_user_id: z.number().optional(),
-  priority: z.number().optional(),
+  // The legacy route accepted both boolean and 0/1 for checked — both stay valid.
+  checked: z.union([z.boolean(), z.number().int().min(0).max(1)]).optional(),
+  // Nullable fields follow the bodyKeys protocol: a key present with null
+  // clears the field, an omitted key leaves it unchanged.
+  category: z.string().nullable().optional(),
+  due_date: z.string().nullable().optional(),
+  description: z.string().nullable().optional(),
+  assigned_user_id: z.number().nullable().optional(),
+  priority: z.number().nullable().optional(),
 });
 export type TodoUpdateItemRequest = z.infer<typeof todoUpdateItemRequestSchema>;