feat(config): update fallback model handling to support multiple models

internal/ai/litellm/client.go

@@ -9,22 +9,22 @@ import (
 )
 
 func New(cfg config.AIConfig, httpClient *http.Client, log *slog.Logger) (*compat.Client, error) {
-	fallback := cfg.LiteLLM.FallbackMetadataModel
-	if fallback == "" {
-		fallback = cfg.Metadata.FallbackModel
+	fallbacks := cfg.LiteLLM.EffectiveFallbackMetadataModels()
+	if len(fallbacks) == 0 {
+		fallbacks = cfg.Metadata.EffectiveFallbackModels()
 	}
 	return compat.New(compat.Config{
-		Name:                  "litellm",
-		BaseURL:               cfg.LiteLLM.BaseURL,
-		APIKey:                cfg.LiteLLM.APIKey,
-		EmbeddingModel:        cfg.LiteLLM.EmbeddingModel,
-		MetadataModel:         cfg.LiteLLM.MetadataModel,
-		FallbackMetadataModel: fallback,
-		Temperature:           cfg.Metadata.Temperature,
-		Headers:               cfg.LiteLLM.RequestHeaders,
-		HTTPClient:            httpClient,
-		Log:                   log,
-		Dimensions:            cfg.Embeddings.Dimensions,
-		LogConversations:      cfg.Metadata.LogConversations,
+		Name:                   "litellm",
+		BaseURL:                cfg.LiteLLM.BaseURL,
+		APIKey:                 cfg.LiteLLM.APIKey,
+		EmbeddingModel:         cfg.LiteLLM.EmbeddingModel,
+		MetadataModel:          cfg.LiteLLM.MetadataModel,
+		FallbackMetadataModels: fallbacks,
+		Temperature:            cfg.Metadata.Temperature,
+		Headers:                cfg.LiteLLM.RequestHeaders,
+		HTTPClient:             httpClient,
+		Log:                    log,
+		Dimensions:             cfg.Embeddings.Dimensions,
+		LogConversations:       cfg.Metadata.LogConversations,
 	}), nil
 }