feat(amp): enhance model mapping and Gemini thinking configuration

This commit introduces several improvements to the AMP (Advanced Model Proxy) module:

- **Model Mapping Logic:** The `FallbackHandler` now uses a more robust approach for model mapping. It includes the extraction and preservation of dynamic "thinking suffixes" (e.g., `(xhigh)`) during mapping, ensuring that these configurations are correctly applied to the mapped model. A new `resolveMappedModel` function centralizes this logic for cleaner code.
- **ModelMapper Verification:** The `ModelMapper` in `model_mapping.go` now verifies that the target model of a mapping has available providers *after* normalizing it. This prevents mappings to non-existent or unresolvable models.
- **Gemini Thinking Configuration Cleanup:** In `gemini_thinking.go`, unnecessary `generationConfig.thinkingConfig.include_thoughts` and `generationConfig.thinkingConfig.thinkingBudget` fields are now deleted from the request body when applying Gemini thinking levels. This prevents potential conflicts or redundant configurations.
- **Testing:** A new test case `TestModelMapper_MapModel_TargetWithThinkingSuffix` has been added to `model_mapping_test.go` to specifically cover the preservation of thinking suffixes during model mapping.

internal/api/modules/amp/fallback_handlers.go

@@ -134,7 +134,43 @@ func (fh *FallbackHandler) WrapHandler(handler gin.HandlerFunc) gin.HandlerFunc
 		}
 
 		// Normalize model (handles dynamic thinking suffixes)
-		normalizedModel, _ := util.NormalizeThinkingModel(modelName)
+		normalizedModel, thinkingMetadata := util.NormalizeThinkingModel(modelName)
+		thinkingSuffix := ""
+		if thinkingMetadata != nil && strings.HasPrefix(modelName, normalizedModel) {
+			thinkingSuffix = modelName[len(normalizedModel):]
+		}
+
+		resolveMappedModel := func() (string, []string) {
+			if fh.modelMapper == nil {
+				return "", nil
+			}
+
+			mappedModel := fh.modelMapper.MapModel(modelName)
+			if mappedModel == "" {
+				mappedModel = fh.modelMapper.MapModel(normalizedModel)
+			}
+			mappedModel = strings.TrimSpace(mappedModel)
+			if mappedModel == "" {
+				return "", nil
+			}
+
+			// Preserve dynamic thinking suffix (e.g. "(xhigh)") when mapping applies, unless the target
+			// already specifies its own thinking suffix.
+			if thinkingSuffix != "" {
+				_, mappedThinkingMetadata := util.NormalizeThinkingModel(mappedModel)
+				if mappedThinkingMetadata == nil {
+					mappedModel += thinkingSuffix
+				}
+			}
+
+			mappedBaseModel, _ := util.NormalizeThinkingModel(mappedModel)
+			mappedProviders := util.GetProviderName(mappedBaseModel)
+			if len(mappedProviders) == 0 {
+				return "", nil
+			}
+
+			return mappedModel, mappedProviders
+		}
 
 		// Track resolved model for logging (may change if mapping is applied)
 		resolvedModel := normalizedModel
@@ -147,21 +183,15 @@ func (fh *FallbackHandler) WrapHandler(handler gin.HandlerFunc) gin.HandlerFunc
 		if forceMappings {
 			// FORCE MODE: Check model mappings FIRST (takes precedence over local API keys)
 			// This allows users to route Amp requests to their preferred OAuth providers
-			if fh.modelMapper != nil {
-				if mappedModel := fh.modelMapper.MapModel(normalizedModel); mappedModel != "" {
-					// Mapping found - check if we have a provider for the mapped model
-					mappedProviders := util.GetProviderName(mappedModel)
-					if len(mappedProviders) > 0 {
-						// Mapping found and provider available - rewrite the model in request body
-						bodyBytes = rewriteModelInRequest(bodyBytes, mappedModel)
-						c.Request.Body = io.NopCloser(bytes.NewReader(bodyBytes))
-						// Store mapped model in context for handlers that check it (like gemini bridge)
-						c.Set(MappedModelContextKey, mappedModel)
-						resolvedModel = mappedModel
-						usedMapping = true
-						providers = mappedProviders
-					}
-				}
+			if mappedModel, mappedProviders := resolveMappedModel(); mappedModel != "" {
+				// Mapping found and provider available - rewrite the model in request body
+				bodyBytes = rewriteModelInRequest(bodyBytes, mappedModel)
+				c.Request.Body = io.NopCloser(bytes.NewReader(bodyBytes))
+				// Store mapped model in context for handlers that check it (like gemini bridge)
+				c.Set(MappedModelContextKey, mappedModel)
+				resolvedModel = mappedModel
+				usedMapping = true
+				providers = mappedProviders
 			}
 
 			// If no mapping applied, check for local providers
@@ -174,21 +204,15 @@ func (fh *FallbackHandler) WrapHandler(handler gin.HandlerFunc) gin.HandlerFunc
 
 			if len(providers) == 0 {
 				// No providers configured - check if we have a model mapping
-				if fh.modelMapper != nil {
-					if mappedModel := fh.modelMapper.MapModel(normalizedModel); mappedModel != "" {
-						// Mapping found - check if we have a provider for the mapped model
-						mappedProviders := util.GetProviderName(mappedModel)
-						if len(mappedProviders) > 0 {
-							// Mapping found and provider available - rewrite the model in request body
-							bodyBytes = rewriteModelInRequest(bodyBytes, mappedModel)
-							c.Request.Body = io.NopCloser(bytes.NewReader(bodyBytes))
-							// Store mapped model in context for handlers that check it (like gemini bridge)
-							c.Set(MappedModelContextKey, mappedModel)
-							resolvedModel = mappedModel
-							usedMapping = true
-							providers = mappedProviders
-						}
-					}
+				if mappedModel, mappedProviders := resolveMappedModel(); mappedModel != "" {
+					// Mapping found and provider available - rewrite the model in request body
+					bodyBytes = rewriteModelInRequest(bodyBytes, mappedModel)
+					c.Request.Body = io.NopCloser(bytes.NewReader(bodyBytes))
+					// Store mapped model in context for handlers that check it (like gemini bridge)
+					c.Set(MappedModelContextKey, mappedModel)
+					resolvedModel = mappedModel
+					usedMapping = true
+					providers = mappedProviders
 				}
 			}
 		}
@@ -222,14 +246,14 @@ func (fh *FallbackHandler) WrapHandler(handler gin.HandlerFunc) gin.HandlerFunc
 			// Log: Model was mapped to another model
 			log.Debugf("amp model mapping: request %s -> %s", normalizedModel, resolvedModel)
 			logAmpRouting(RouteTypeModelMapping, modelName, resolvedModel, providerName, requestPath)
-			rewriter := NewResponseRewriter(c.Writer, normalizedModel)
+			rewriter := NewResponseRewriter(c.Writer, modelName)
 			c.Writer = rewriter
 			// Filter Anthropic-Beta header only for local handling paths
 			filterAntropicBetaHeader(c)
 			c.Request.Body = io.NopCloser(bytes.NewReader(bodyBytes))
 			handler(c)
 			rewriter.Flush()
-			log.Debugf("amp model mapping: response %s -> %s", resolvedModel, normalizedModel)
+			log.Debugf("amp model mapping: response %s -> %s", resolvedModel, modelName)
 		} else if len(providers) > 0 {
 			// Log: Using local provider (free)
 			logAmpRouting(RouteTypeLocalProvider, modelName, resolvedModel, providerName, requestPath)

internal/api/modules/amp/fallback_handlers_test.go

@@ -0,0 +1,73 @@
+package amp
+
+import (
+	"bytes"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"net/http/httputil"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/registry"
+)
+
+func TestFallbackHandler_ModelMapping_PreservesThinkingSuffixAndRewritesResponse(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	reg := registry.GetGlobalRegistry()
+	reg.RegisterClient("test-client-amp-fallback", "codex", []*registry.ModelInfo{
+		{ID: "test/gpt-5.2", OwnedBy: "openai", Type: "codex"},
+	})
+	defer reg.UnregisterClient("test-client-amp-fallback")
+
+	mapper := NewModelMapper([]config.AmpModelMapping{
+		{From: "gpt-5.2", To: "test/gpt-5.2"},
+	})
+
+	fallback := NewFallbackHandlerWithMapper(func() *httputil.ReverseProxy { return nil }, mapper, nil)
+
+	handler := func(c *gin.Context) {
+		var req struct {
+			Model string `json:"model"`
+		}
+		if err := c.ShouldBindJSON(&req); err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+			return
+		}
+
+		c.JSON(http.StatusOK, gin.H{
+			"model":      req.Model,
+			"seen_model": req.Model,
+		})
+	}
+
+	r := gin.New()
+	r.POST("/chat/completions", fallback.WrapHandler(handler))
+
+	reqBody := []byte(`{"model":"gpt-5.2(xhigh)"}`)
+	req := httptest.NewRequest(http.MethodPost, "/chat/completions", bytes.NewReader(reqBody))
+	req.Header.Set("Content-Type", "application/json")
+	w := httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("Expected status 200, got %d", w.Code)
+	}
+
+	var resp struct {
+		Model     string `json:"model"`
+		SeenModel string `json:"seen_model"`
+	}
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("Failed to parse response JSON: %v", err)
+	}
+
+	if resp.Model != "gpt-5.2(xhigh)" {
+		t.Errorf("Expected response model gpt-5.2(xhigh), got %s", resp.Model)
+	}
+	if resp.SeenModel != "test/gpt-5.2(xhigh)" {
+		t.Errorf("Expected handler to see test/gpt-5.2(xhigh), got %s", resp.SeenModel)
+	}
+}

internal/api/modules/amp/model_mapping.go

@@ -59,7 +59,8 @@ func (m *DefaultModelMapper) MapModel(requestedModel string) string {
 	}
 
 	// Verify target model has available providers
-	providers := util.GetProviderName(targetModel)
+	normalizedTarget, _ := util.NormalizeThinkingModel(targetModel)
+	providers := util.GetProviderName(normalizedTarget)
 	if len(providers) == 0 {
 		log.Debugf("amp model mapping: target model %s has no available providers, skipping mapping", targetModel)
 		return ""

internal/api/modules/amp/model_mapping_test.go

@@ -71,6 +71,25 @@ func TestModelMapper_MapModel_WithProvider(t *testing.T) {
 	}
 }
 
+func TestModelMapper_MapModel_TargetWithThinkingSuffix(t *testing.T) {
+	reg := registry.GetGlobalRegistry()
+	reg.RegisterClient("test-client-thinking", "codex", []*registry.ModelInfo{
+		{ID: "gpt-5.2", OwnedBy: "openai", Type: "codex"},
+	})
+	defer reg.UnregisterClient("test-client-thinking")
+
+	mappings := []config.AmpModelMapping{
+		{From: "gpt-5.2-alias", To: "gpt-5.2(xhigh)"},
+	}
+
+	mapper := NewModelMapper(mappings)
+
+	result := mapper.MapModel("gpt-5.2-alias")
+	if result != "gpt-5.2(xhigh)" {
+		t.Errorf("Expected gpt-5.2(xhigh), got %s", result)
+	}
+}
+
 func TestModelMapper_MapModel_CaseInsensitive(t *testing.T) {
 	reg := registry.GetGlobalRegistry()
 	reg.RegisterClient("test-client2", "claude", []*registry.ModelInfo{