feat: add stream_item_content method for async content streaming

Co-authored-by: aider (openai/andrew/openrouter/qwen/qwen3-coder) <aider@aider.chat>

src/services/async_item_service.rs

@@ -51,6 +51,57 @@ impl AsyncItemService {
         .unwrap()
     }
 
+    pub async fn stream_item_content(
+        &self,
+        item_id: i64,
+        allow_binary: bool,
+        offset: u64,
+        length: u64,
+    ) -> Result<(impl tokio_stream::Stream<Item = Result<bytes::Bytes, std::io::Error>>, String), CoreError> {
+        let item_with_content = self.get_item_content(item_id).await?;
+        let metadata = item_with_content.item_with_meta.meta_as_map();
+        
+        // Check if content is binary when allow_binary is false
+        if !allow_binary {
+            let is_content_binary = if let Some(binary_val) = metadata.get("binary") {
+                binary_val == "true"
+            } else {
+                // If binary metadata not available, check the actual content
+                is_binary(&item_with_content.content)
+            };
+            
+            if is_content_binary {
+                return Err(CoreError::InvalidInput("Binary content not allowed".to_string()));
+            }
+        }
+        
+        let mime_type = metadata
+            .get("mime_type")
+            .map(|s| s.to_string())
+            .unwrap_or_else(|| "application/octet-stream".to_string());
+        
+        // Open the file for streaming
+        let file_path = self.data_path.join(format!("{}.dat", item_id));
+        let file = tokio::fs::File::open(&file_path).await?;
+        let mut buffered_file = tokio::io::BufReader::new(file);
+        
+        // Seek to the requested offset if needed
+        if offset > 0 {
+            buffered_file.seek(std::io::SeekFrom::Start(offset)).await?;
+        }
+        
+        // Create a reader stream with optional length limit
+        let stream = if length > 0 {
+            // Limit the stream to the specified length
+            ReaderStream::new(buffered_file.take(length))
+        } else {
+            // Stream the entire file from the offset
+            ReaderStream::new(buffered_file)
+        };
+        
+        Ok((stream, mime_type))
+    }
+
     pub async fn find_item(
         &self,
         ids: Vec<i64>,