feat(config): add fallback model support for AI configurations

internal/ai/compat/client.go

@@ -33,29 +33,31 @@ Rules:
 - Do not include any text outside the JSON object.`
 
 type Client struct {
-	name           string
-	baseURL        string
-	apiKey         string
-	embeddingModel string
-	metadataModel  string
-	temperature    float64
-	headers        map[string]string
-	httpClient     *http.Client
-	log            *slog.Logger
-	dimensions     int
+	name                  string
+	baseURL               string
+	apiKey                string
+	embeddingModel        string
+	metadataModel         string
+	fallbackMetadataModel string
+	temperature           float64
+	headers               map[string]string
+	httpClient            *http.Client
+	log                   *slog.Logger
+	dimensions            int
 }
 
 type Config struct {
-	Name           string
-	BaseURL        string
-	APIKey         string
-	EmbeddingModel string
-	MetadataModel  string
-	Temperature    float64
-	Headers        map[string]string
-	HTTPClient     *http.Client
-	Log            *slog.Logger
-	Dimensions     int
+	Name                  string
+	BaseURL               string
+	APIKey                string
+	EmbeddingModel        string
+	MetadataModel         string
+	FallbackMetadataModel string
+	Temperature           float64
+	Headers               map[string]string
+	HTTPClient            *http.Client
+	Log                   *slog.Logger
+	Dimensions            int
 }
 
 type embeddingsRequest struct {
@@ -100,16 +102,17 @@ type providerError struct {
 
 func New(cfg Config) *Client {
 	return &Client{
-		name:           cfg.Name,
-		baseURL:        cfg.BaseURL,
-		apiKey:         cfg.APIKey,
-		embeddingModel: cfg.EmbeddingModel,
-		metadataModel:  cfg.MetadataModel,
-		temperature:    cfg.Temperature,
-		headers:        cfg.Headers,
-		httpClient:     cfg.HTTPClient,
-		log:            cfg.Log,
-		dimensions:     cfg.Dimensions,
+		name:                  cfg.Name,
+		baseURL:               cfg.BaseURL,
+		apiKey:                cfg.APIKey,
+		embeddingModel:        cfg.EmbeddingModel,
+		metadataModel:         cfg.MetadataModel,
+		fallbackMetadataModel: cfg.FallbackMetadataModel,
+		temperature:           cfg.Temperature,
+		headers:               cfg.Headers,
+		httpClient:            cfg.HTTPClient,
+		log:                   cfg.Log,
+		dimensions:            cfg.Dimensions,
 	}
 }
 
@@ -146,8 +149,24 @@ func (c *Client) ExtractMetadata(ctx context.Context, input string) (thoughttype
 		return thoughttypes.ThoughtMetadata{}, fmt.Errorf("%s extract metadata: input must not be empty", c.name)
 	}
 
+	result, err := c.extractMetadataWithModel(ctx, input, c.metadataModel)
+	if err != nil && c.fallbackMetadataModel != "" && ctx.Err() == nil {
+		if c.log != nil {
+			c.log.Warn("metadata extraction failed, trying fallback model",
+				slog.String("provider", c.name),
+				slog.String("primary_model", c.metadataModel),
+				slog.String("fallback_model", c.fallbackMetadataModel),
+				slog.String("error", err.Error()),
+			)
+		}
+		return c.extractMetadataWithModel(ctx, input, c.fallbackMetadataModel)
+	}
+	return result, err
+}
+
+func (c *Client) extractMetadataWithModel(ctx context.Context, input, model string) (thoughttypes.ThoughtMetadata, error) {
 	req := chatCompletionsRequest{
-		Model:       c.metadataModel,
+		Model:       model,
 		Temperature: c.temperature,
 		ResponseFormat: &responseType{
 			Type: "json_object",
@@ -172,6 +191,9 @@ func (c *Client) ExtractMetadata(ctx context.Context, input string) (thoughttype
 	metadataText := strings.TrimSpace(resp.Choices[0].Message.Content)
 	metadataText = stripCodeFence(metadataText)
 	metadataText = extractJSONObject(metadataText)
+	if metadataText == "" {
+		return thoughttypes.ThoughtMetadata{}, fmt.Errorf("%s metadata: response contains no JSON object", c.name)
+	}
 
 	var metadata thoughttypes.ThoughtMetadata
 	if err := json.Unmarshal([]byte(metadataText), &metadata); err != nil {
@@ -241,7 +263,7 @@ func (c *Client) doJSON(ctx context.Context, path string, requestBody any, dest
 		resp, err := c.httpClient.Do(req)
 		if err != nil {
 			lastErr = fmt.Errorf("%s request failed: %w", c.name, err)
-			if attempt < maxAttempts && isRetryableError(err) {
+			if attempt < maxAttempts && ctx.Err() == nil && isRetryableError(err) {
 				if retryErr := sleepRetry(ctx, attempt, c.log, c.name); retryErr != nil {
 					return retryErr
 				}
@@ -293,7 +315,7 @@ func extractJSONObject(s string) string {
 	start := strings.Index(s, "{")
 	end := strings.LastIndex(s, "}")
 	if start == -1 || end == -1 || end <= start {
-		return s
+		return ""
 	}
 	return s[start : end+1]
 }