fix(push): add cross-tenant ownership check to DeleteAll + clean up owners map

DeleteAll previously had no ownership verification, allowing any caller
to delete arbitrary task push configs — a cross-tenant isolation bypass.

Changes:
- DeleteAll now calls checkOwner (same pattern as Delete) and returns
  ErrTaskNotFound for cross-tenant access or nil for never-saved tasks.
- DeleteAll now cleans up s.owners[taskID] to prevent stale owner
  entries after all configs are removed.
- CrossTenantIsolation test extended to cover DeleteAll.

Author: 邝谧

a2asrv/push/store.go

@@ -220,10 +220,19 @@ func (s *InMemoryPushConfigStore) Delete(ctx context.Context, taskID a2a.TaskID,
 	return nil
 }
 
-// DeleteAll removes all stored configs for a task.
+// DeleteAll removes all stored configs for a task owned by the caller.
 func (s *InMemoryPushConfigStore) DeleteAll(ctx context.Context, taskID a2a.TaskID) error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
+
+	if err := s.checkOwner(ctx, taskID); err != nil {
+		if errors.Is(err, errNoOwner) {
+			return nil // idempotent — task never existed
+		}
+		return err
+	}
+
 	delete(s.configs, taskID)
+	delete(s.owners, taskID)
 	return nil
 }

a2asrv/push/store_test.go

@@ -479,6 +479,9 @@ func TestInMemoryPushConfigStore_CrossTenantIsolation(t *testing.T) {
 	if err := store.Delete(bobCtx, taskID, cfg.ID); err == nil {
 		t.Fatal("bob Delete should have failed with cross-tenant access")
 	}
+	if err := store.DeleteAll(bobCtx, taskID); err == nil {
+		t.Fatal("bob DeleteAll should have failed with cross-tenant access")
+	}
 
 	// Alice can still access her own configs.
 	got, err := store.Get(aliceCtx, taskID, cfg.ID)