**[feature/openrouter-provider] Add support for custom headers in OpenAI client configuration**

- Introduced a new `extraHeaders` field in the `openaiOptions` struct to allow specifying additional HTTP headers.
- Added logic in `newOpenAIClient` to apply `extraHeaders` to the OpenAI client configuration.
- Implemented a new option function `WithOpenAIExtraHeaders` to set custom headers in `openaiOptions`.
- Updated the OpenRouter provider configuration in `NewProvider` to include default headers (`HTTP-Referer` and `X-Title`) for OpenRouter API requests.

Author: isaac-scarrott

internal/llm/provider/openai.go

@@ -21,6 +21,7 @@ type openaiOptions struct {
 	baseURL         string
 	disableCache    bool
 	reasoningEffort string
+	extraHeaders    map[string]string
 }
 
 type OpenAIOption func(*openaiOptions)
@@ -49,6 +50,12 @@ func newOpenAIClient(opts providerClientOptions) OpenAIClient {
 		openaiClientOptions = append(openaiClientOptions, option.WithBaseURL(openaiOpts.baseURL))
 	}
 
+	if openaiOpts.extraHeaders != nil {
+		for key, value := range openaiOpts.extraHeaders {
+			openaiClientOptions = append(openaiClientOptions, option.WithHeader(key, value))
+		}
+	}
+
 	client := openai.NewClient(openaiClientOptions...)
 	return &openaiClient{
 		providerOptions: opts,
@@ -392,6 +399,12 @@ func WithOpenAIBaseURL(baseURL string) OpenAIOption {
 	}
 }
 
+func WithOpenAIExtraHeaders(headers map[string]string) OpenAIOption {
+	return func(options *openaiOptions) {
+		options.extraHeaders = headers
+	}
+}
+
 func WithOpenAIDisableCache() OpenAIOption {
 	return func(options *openaiOptions) {
 		options.disableCache = true

internal/llm/provider/provider.go

@@ -118,6 +118,10 @@ func NewProvider(providerName models.ModelProvider, opts ...ProviderClientOption
 	case models.ProviderOpenRouter:
 		clientOptions.openaiOptions = append(clientOptions.openaiOptions,
 			WithOpenAIBaseURL("https://openrouter.ai/api/v1"),
+			WithOpenAIExtraHeaders(map[string]string{
+				"HTTP-Referer": "opencode.ai",
+				"X-Title":      "OpenCode",
+			}),
 		)
 		return &baseProvider[OpenAIClient]{
 			options: clientOptions,