fix(server): filter out attachment in pplx provider (#11986)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

- **Bug Fixes**
  - Improved handling of messages without attachments, ensuring a placeholder is shown when content is empty and attachments are omitted.
- **New Features**
  - Added the ability to selectively include or exclude attachments in message processing.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/providers/perplexity.ts

@@ -82,7 +82,7 @@ export class PerplexityProvider
     try {
       metrics.ai.counter('chat_text_calls').add(1, { model });
 
-      const [system, msgs] = await chatToGPTMessage(messages);
+      const [system, msgs] = await chatToGPTMessage(messages, false);
 
       const modelInstance = this.#instance(model);
 
@@ -119,7 +119,7 @@ export class PerplexityProvider
     try {
       metrics.ai.counter('chat_text_stream_calls').add(1, { model });
 
-      const [system, msgs] = await chatToGPTMessage(messages);
+      const [system, msgs] = await chatToGPTMessage(messages, false);
 
       const modelInstance = this.#instance(model);
 

packages/backend/server/src/plugins/copilot/providers/utils.ts

@@ -58,7 +58,9 @@ async function inferMimeType(url: string) {
 }
 
 export async function chatToGPTMessage(
-  messages: PromptMessage[]
+  messages: PromptMessage[],
+  // TODO(@darkskygit): move this logic in interface refactoring
+  withAttachment: boolean = true
 ): Promise<[string | undefined, ChatMessage[], any]> {
   const system = messages[0]?.role === 'system' ? messages.shift() : undefined;
   const schema = system?.params?.schema;
@@ -77,6 +79,7 @@ export async function chatToGPTMessage(
         contents.push({ type: 'text', text: content });
       }
 
+      if (withAttachment) {
         for (let attachment of attachments) {
           let mimeType: string;
           if (typeof attachment === 'string') {
@@ -98,6 +101,10 @@ export async function chatToGPTMessage(
             }
           }
         }
+      } else if (!content.length) {
+        // temp fix for pplx
+        contents.push({ type: 'text', text: '[no content]' });
+      }
 
       msgs.push({ role, content: contents } as ChatMessage);
     } else {