fix(alicode): preserve cache_control for DashScope providers (#2069)

Opt-in quirk preserveCacheControl keeps cache_control on content blocks
for alicode/alicode-intl, enabling DashScope prompt caching. signature
is always stripped; all other providers unchanged.

Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/translator/index.js

@@ -109,7 +109,9 @@ export function translateRequest(sourceFormat, targetFormat, model, body, stream
   // Always normalize to clean OpenAI format when target is OpenAI
   // This handles hybrid requests (e.g., OpenAI messages + Claude tools)
   if (targetFormat === FORMATS.OPENAI) {
-    result = filterToOpenAIFormat(result);
+    result = filterToOpenAIFormat(result, {
+      preserveCacheControl: !!PROVIDERS[provider]?.quirks?.preserveCacheControl,
+    });
   }
 
   // Final step: prepare request for Claude format endpoints