Support camelCase Gemini params and validate vision

src/proxy/middleware/request/preprocessors/transform-outbound-payload.ts

@@ -30,6 +30,7 @@ export const transformOutboundPayload: RequestPreprocessor = async (req) => {
   }
 
   applyMistralPromptFixes(req);
+  applyGoogleAIKeyTransforms(req);
 
   // Native prompts are those which were already provided by the client in the
   // target API format. We don't need to transform them.
@@ -87,3 +88,43 @@ function applyMistralPromptFixes(req: Request): void {
     }
   }
 }
+
+function toSnakeCase(str: string): string {
+  return str.replace(/[A-Z]/g, letter => `_${letter.toLowerCase()}`);
+}
+
+function transformKeysToSnakeCase(obj: any, hasTransformed = { value: false }): any {
+  if (Array.isArray(obj)) {
+    return obj.map(item => transformKeysToSnakeCase(item, hasTransformed));
+  }
+  
+  if (obj !== null && typeof obj === 'object') {
+    return Object.fromEntries(
+      Object.entries(obj).map(([key, value]) => {
+        const snakeKey = toSnakeCase(key);
+        if (snakeKey !== key) {
+          hasTransformed.value = true;
+        }
+        return [
+          snakeKey,
+          transformKeysToSnakeCase(value, hasTransformed)
+        ];
+      })
+    );
+  }
+  
+  return obj;
+}
+
+function applyGoogleAIKeyTransforms(req: Request): void {
+  // Google (Gemini) API in their infinite wisdom accepts both snake_case and camelCase
+  // even though in the docs they use snake_case. Some frontends (e.g. ST) use camelCase
+  // so we normalize all keys to snake_case here
+  if (req.outboundApi === "google-ai") {
+    const hasTransformed = { value: false };
+    req.body = transformKeysToSnakeCase(req.body, hasTransformed);
+    if (hasTransformed.value) {
+      req.log.info("Applied Gemini camelCase -> snake_case transform");
+    }
+  }
+}

src/proxy/middleware/request/preprocessors/validate-vision.ts

@@ -3,6 +3,7 @@ import { assertNever } from "../../../../shared/utils";
 import { RequestPreprocessor } from "../index";
 import { containsImageContent as containsImageContentOpenAI } from "../../../../shared/api-schemas/openai";
 import { containsImageContent as containsImageContentAnthropic } from "../../../../shared/api-schemas/anthropic";
+import { containsImageContent as containsImageContentGoogleAI } from "../../../../shared/api-schemas/google-ai";
 import { ForbiddenError } from "../../../../shared/errors";
 
 /**
@@ -25,8 +26,10 @@ export const validateVision: RequestPreprocessor = async (req) => {
     case "anthropic-chat":
       hasImage = containsImageContentAnthropic(req.body.messages);
       break;
-    case "anthropic-text":
     case "google-ai":
+      hasImage = containsImageContentGoogleAI(req.body.contents);
+      break;
+    case "anthropic-text":
     case "mistral-ai":
     case "mistral-text":
     case "openai-image":