feat(gemini-web): Add support for real Nano Banana model

internal/client/gemini-web/client.go

@@ -33,6 +33,10 @@ type GeminiClient struct {
 	accountLabel    string
 }
 
+var NanoBananaModel = map[string]struct{}{
+	"gemini-2.5-flash-image-preview": {},
+}
+
 // NewGeminiClient creates a client. Pass empty strings to auto-detect via browser cookies (not implemented in Go port).
 func NewGeminiClient(secure1psid string, secure1psidts string, proxy string, opts ...func(*GeminiClient)) *GeminiClient {
 	c := &GeminiClient{
@@ -239,6 +243,14 @@ func (c *GeminiClient) GenerateContent(prompt string, files []string, model Mode
 	}
 }
 
+func ensureAnyLen(slice []any, index int) []any {
+	if index < len(slice) {
+		return slice
+	}
+	gap := index + 1 - len(slice)
+	return append(slice, make([]any, gap)...)
+}
+
 func (c *GeminiClient) generateOnce(prompt string, files []string, model Model, gem *Gem, chat *ChatSession) (ModelOutput, error) {
 	var empty ModelOutput
 	// Build f.req
@@ -266,6 +278,14 @@ func (c *GeminiClient) generateOnce(prompt string, files []string, model Model,
 	}
 
 	inner := []any{item0, nil, item2}
+	requestedModel := strings.ToLower(model.Name)
+	if chat != nil && chat.RequestedModel() != "" {
+		requestedModel = chat.RequestedModel()
+	}
+	if _, ok := NanoBananaModel[requestedModel]; ok {
+		inner = ensureAnyLen(inner, 49)
+		inner[49] = 14
+	}
 	if gem != nil {
 		// pad with 16 nils then gem ID
 		for i := 0; i < 16; i++ {
@@ -674,7 +694,7 @@ func truncateForLog(s string, n int) string {
 
 // StartChat returns a ChatSession attached to the client
 func (c *GeminiClient) StartChat(model Model, gem *Gem, metadata []string) *ChatSession {
-	return &ChatSession{client: c, metadata: normalizeMeta(metadata), model: model, gem: gem}
+	return &ChatSession{client: c, metadata: normalizeMeta(metadata), model: model, gem: gem, requestedModel: strings.ToLower(model.Name)}
 }
 
 // ChatSession holds conversation metadata
@@ -684,6 +704,7 @@ type ChatSession struct {
 	lastOutput     *ModelOutput
 	model          Model
 	gem            *Gem
+	requestedModel string
 }
 
 func (cs *ChatSession) String() string {
@@ -710,6 +731,10 @@ func normalizeMeta(v []string) []string {
 
 func (cs *ChatSession) Metadata() []string     { return cs.metadata }
 func (cs *ChatSession) SetMetadata(v []string) { cs.metadata = normalizeMeta(v) }
+func (cs *ChatSession) RequestedModel() string { return cs.requestedModel }
+func (cs *ChatSession) SetRequestedModel(name string) {
+	cs.requestedModel = strings.ToLower(name)
+}
 func (cs *ChatSession) CID() string {
 	if len(cs.metadata) > 0 {
 		return cs.metadata[0]

internal/client/gemini-web_client.go

@@ -394,6 +394,7 @@ func (c *GeminiWebClient) prepareChat(ctx context.Context, modelName string, raw
 	c.appendUpstreamRequestLog(ctx, modelName, res.tagged, true, res.prompt, len(uploadedFiles), res.reuse, res.metaLen)
 	gem := c.getConfiguredGem()
 	res.chat = c.gwc.StartChat(model, gem, meta)
+	res.chat.SetRequestedModel(modelName)
 	return res, nil
 }