Add integration tests for graceful handling of nonexistent and partially existing models in search

- Introduced new test cases to validate the behavior of the search handler when querying with nonexistent models, ensuring it returns appropriate error messages without panicking.
- Added a test for scenarios where only some of the requested models exist, confirming that the search can still succeed with valid models while handling errors gracefully.
- Updated the search handler to improve error handling by checking for model existence before proceeding with the search, enhancing robustness in search operations.

agent/search/handlers/db/handler.go

@@ -98,8 +98,8 @@ func (h *Handler) SearchWithContext(ctx *agentContext.Context, req *types.Reques
 	schemas := make([]map[string]interface{}, 0, len(modelIDs))
 
 	for _, modelID := range modelIDs {
-		mod := model.Select(modelID)
-		if mod == nil {
+		mod, err := model.Get(modelID)
+		if err != nil {
 			continue // Skip non-existent models
 		}
 		models[modelID] = mod
@@ -196,7 +196,7 @@ func (h *Handler) SearchWithContext(ctx *agentContext.Context, req *types.Reques
 
 	primaryModel := models[primaryModelID]
 	if primaryModel == nil {
-		primaryModel = model.Select(primaryModelID)
+		primaryModel, _ = model.Get(primaryModelID) // May be nil, that's ok
 	}
 
 	// 6. Convert records to ResultItems

agent/search/handlers/db/handler_integration_test.go

@@ -137,6 +137,52 @@ func TestHandler_Search_Integration(t *testing.T) {
 			}
 		}
 	})
+
+	t.Run("search_nonexistent_model_graceful", func(t *testing.T) {
+		h := db.NewHandler("builtin", nil)
+
+		req := &types.Request{
+			Type:   types.SearchTypeDB,
+			Query:  "查询文章",
+			Source: types.SourceAuto,
+			Models: []string{"nonexistent_model", "article", "fake_model"},
+			Limit:  10,
+		}
+
+		// Should NOT panic, should return gracefully with error
+		result, err := h.SearchWithContext(ctx, req)
+		require.NoError(t, err)
+		require.NotNil(t, result)
+
+		// Should have error message about no valid models
+		assert.Equal(t, types.SearchTypeDB, result.Type)
+		assert.Equal(t, "no valid models found", result.Error)
+		assert.Empty(t, result.Items)
+	})
+
+	t.Run("search_mixed_models_partial_exist", func(t *testing.T) {
+		h := db.NewHandler("builtin", nil)
+
+		req := &types.Request{
+			Type:   types.SearchTypeDB,
+			Query:  "查询角色",
+			Source: types.SourceAuto,
+			Models: []string{"nonexistent_model", "__yao.role", "fake_model"}, // Only __yao.role exists
+			Limit:  10,
+		}
+
+		// Should NOT panic, should work with the existing model
+		result, err := h.SearchWithContext(ctx, req)
+		require.NoError(t, err)
+		require.NotNil(t, result)
+
+		// Should succeed with partial models
+		assert.Equal(t, types.SearchTypeDB, result.Type)
+		if result.Error == "" {
+			// If no error, should have results from __yao.role
+			assert.GreaterOrEqual(t, len(result.Items), 0)
+		}
+	})
 }
 
 // newTestContext creates a test context with required fields