Filter thought parts before passing them to CountToken (#6859)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Arya Gummadi <aryagummadi@google.com>

packages/core/src/code_assist/converter.ts

@@ -189,13 +189,18 @@ function toContent(content: ContentUnion): Content {
     };
   }
   if ('parts' in content) {
-    // it's a Content
-    return content;
+    // it's a Content - process parts to handle thought filtering
+    return {
+      ...content,
+      parts: content.parts
+        ? toParts(content.parts.filter((p) => p != null))
+        : [],
+    };
   }
   // it's a Part
   return {
     role: 'user',
-    parts: [content as Part],
+    parts: [toPart(content as Part)],
   };
 }
 
@@ -208,6 +213,41 @@ function toPart(part: PartUnion): Part {
     // it's a string
     return { text: part };
   }
+
+  // Handle thought parts for CountToken API compatibility
+  // The CountToken API expects parts to have certain required "oneof" fields initialized,
+  // but thought parts don't conform to this schema and cause API failures
+  if ('thought' in part && part.thought) {
+    const thoughtText = `[Thought: ${part.thought}]`;
+
+    const newPart = { ...part };
+    delete (newPart as Record<string, unknown>)['thought'];
+
+    const hasApiContent =
+      'functionCall' in newPart ||
+      'functionResponse' in newPart ||
+      'inlineData' in newPart ||
+      'fileData' in newPart;
+
+    if (hasApiContent) {
+      // It's a functionCall or other non-text part. Just strip the thought.
+      return newPart;
+    }
+
+    // If no other valid API content, this must be a text part.
+    // Combine existing text (if any) with the thought, preserving other properties.
+    const text = (newPart as { text?: unknown }).text;
+    const existingText = text ? String(text) : '';
+    const combinedText = existingText
+      ? `${existingText}\n${thoughtText}`
+      : thoughtText;
+
+    return {
+      ...newPart,
+      text: combinedText,
+    };
+  }
+
   return part;
 }