feature(ampcode): Improves AMP model mapping with alias support

Enhances the AMP model mapping functionality to support fallback mechanisms using .

This change allows the system to attempt alternative models (aliases) if the primary mapped model fails due to issues like quota exhaustion. It updates the model mapper to load and utilize the  configuration, enabling provider lookup via aliases. It also introduces context keys to pass fallback model names between handlers.

Additionally, this change introduces a fix to prevent ReverseProxy from panicking by swallowing ErrAbortHandler panics.

Amp-Thread-ID: https://ampcode.com/threads/T-019c0cd1-9e59-722b-83f0-e0582aba6914
Co-authored-by: Amp <amp@ampcode.com>

internal/api/modules/amp/fallback_handlers.go

@@ -2,7 +2,9 @@ package amp
 
 import (
 	"bytes"
+	"errors"
 	"io"
+	"net/http"
 	"net/http/httputil"
 	"strings"
 	"time"
@@ -32,6 +34,10 @@ const (
 // MappedModelContextKey is the Gin context key for passing mapped model names.
 const MappedModelContextKey = "mapped_model"
 
+// FallbackModelsContextKey is the Gin context key for passing fallback model names.
+// When the primary mapped model fails (e.g., quota exceeded), these models can be tried.
+const FallbackModelsContextKey = "fallback_models"
+
 // logAmpRouting logs the routing decision for an Amp request with structured fields
 func logAmpRouting(routeType AmpRouteType, requestedModel, resolvedModel, provider, path string) {
 	fields := log.Fields{
@@ -113,6 +119,16 @@ func (fh *FallbackHandler) SetModelMapper(mapper ModelMapper) {
 // If the model's provider is not configured in CLIProxyAPI, it forwards to ampcode.com
 func (fh *FallbackHandler) WrapHandler(handler gin.HandlerFunc) gin.HandlerFunc {
 	return func(c *gin.Context) {
+		// Swallow ErrAbortHandler panics from ReverseProxy copyResponse to avoid noisy stack traces
+		defer func() {
+			if rec := recover(); rec != nil {
+				if err, ok := rec.(error); ok && errors.Is(err, http.ErrAbortHandler) {
+					return
+				}
+				panic(rec)
+			}
+		}()
+
 		requestPath := c.Request.URL.Path
 
 		// Read the request body to extract the model name
@@ -142,36 +158,57 @@ func (fh *FallbackHandler) WrapHandler(handler gin.HandlerFunc) gin.HandlerFunc
 			thinkingSuffix = "(" + suffixResult.RawSuffix + ")"
 		}
 
-		resolveMappedModel := func() (string, []string) {
+		// resolveMappedModels returns all mapped models (primary + fallbacks) and providers for the first one.
+		resolveMappedModels := func() ([]string, []string) {
 			if fh.modelMapper == nil {
-				return "", nil
+				return nil, nil
 			}
 
-			mappedModel := fh.modelMapper.MapModel(modelName)
-			if mappedModel == "" {
-				mappedModel = fh.modelMapper.MapModel(normalizedModel)
-			}
-			mappedModel = strings.TrimSpace(mappedModel)
-			if mappedModel == "" {
-				return "", nil
+			mapper, ok := fh.modelMapper.(*DefaultModelMapper)
+			if !ok {
+				// Fallback to single model for non-DefaultModelMapper
+				mappedModel := fh.modelMapper.MapModel(modelName)
+				if mappedModel == "" {
+					mappedModel = fh.modelMapper.MapModel(normalizedModel)
+				}
+				if mappedModel == "" {
+					return nil, nil
+				}
+				mappedBaseModel := thinking.ParseSuffix(mappedModel).ModelName
+				mappedProviders := util.GetProviderName(mappedBaseModel)
+				if len(mappedProviders) == 0 {
+					return nil, nil
+				}
+				return []string{mappedModel}, mappedProviders
 			}
 
-			// Preserve dynamic thinking suffix (e.g. "(xhigh)") when mapping applies, unless the target
-			// already specifies its own thinking suffix.
-			if thinkingSuffix != "" {
-				mappedSuffixResult := thinking.ParseSuffix(mappedModel)
-				if !mappedSuffixResult.HasSuffix {
-					mappedModel += thinkingSuffix
+			// Use MapModelWithFallbacks for DefaultModelMapper
+			mappedModels := mapper.MapModelWithFallbacks(modelName)
+			if len(mappedModels) == 0 {
+				mappedModels = mapper.MapModelWithFallbacks(normalizedModel)
+			}
+			if len(mappedModels) == 0 {
+				return nil, nil
+			}
+
+			// Apply thinking suffix if needed
+			for i, model := range mappedModels {
+				if thinkingSuffix != "" {
+					suffixResult := thinking.ParseSuffix(model)
+					if !suffixResult.HasSuffix {
+						mappedModels[i] = model + thinkingSuffix
+					}
 				}
 			}
 
-			mappedBaseModel := thinking.ParseSuffix(mappedModel).ModelName
-			mappedProviders := util.GetProviderName(mappedBaseModel)
-			if len(mappedProviders) == 0 {
-				return "", nil
+			// Get providers for the first model
+			firstBaseModel := thinking.ParseSuffix(mappedModels[0]).ModelName
+			providers := util.GetProviderName(firstBaseModel)
+			if len(providers) == 0 {
+				return nil, nil
 			}
 
-			return mappedModel, mappedProviders
+			return mappedModels, providers
 		}
 
 		// Track resolved model for logging (may change if mapping is applied)
@@ -185,13 +222,16 @@ 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 mappedModel, mappedProviders := resolveMappedModel(); mappedModel != "" {
+			if mappedModels, mappedProviders := resolveMappedModels(); len(mappedModels) > 0 {
 				// Mapping found and provider available - rewrite the model in request body
-				bodyBytes = rewriteModelInRequest(bodyBytes, mappedModel)
+				bodyBytes = rewriteModelInRequest(bodyBytes, mappedModels[0])
 				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
+				// Store mapped model and fallbacks in context for handlers
+				c.Set(MappedModelContextKey, mappedModels[0])
+				if len(mappedModels) > 1 {
+					c.Set(FallbackModelsContextKey, mappedModels[1:])
+				}
+				resolvedModel = mappedModels[0]
 				usedMapping = true
 				providers = mappedProviders
 			}
@@ -206,13 +246,16 @@ func (fh *FallbackHandler) WrapHandler(handler gin.HandlerFunc) gin.HandlerFunc
 
 			if len(providers) == 0 {
 				// No providers configured - check if we have a model mapping
-				if mappedModel, mappedProviders := resolveMappedModel(); mappedModel != "" {
+				if mappedModels, mappedProviders := resolveMappedModels(); len(mappedModels) > 0 {
 					// Mapping found and provider available - rewrite the model in request body
-					bodyBytes = rewriteModelInRequest(bodyBytes, mappedModel)
+					bodyBytes = rewriteModelInRequest(bodyBytes, mappedModels[0])
 					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
+					// Store mapped model and fallbacks in context for handlers
+					c.Set(MappedModelContextKey, mappedModels[0])
+					if len(mappedModels) > 1 {
+						c.Set(FallbackModelsContextKey, mappedModels[1:])
+					}
+					resolvedModel = mappedModels[0]
 					usedMapping = true
 					providers = mappedProviders
 				}