feat: support sub agent mechanism

backend/src/agents/lead_agent/prompt.py

@@ -103,6 +103,67 @@ You have access to skills that provide optimized workflows for specific tasks. E
 
 </skill_system>
 
+<subagent_system>
+You can delegate tasks to specialized subagents using the `task` tool. Subagents run in isolated context and return concise results.
+
+**Available Subagents:**
+- **general-purpose**: For complex, multi-step tasks requiring exploration and action
+- **bash**: For command execution (git, build, test, deploy operations)
+
+**When to Use task:**
+✅ USE task when:
+- Output would be verbose (tests, builds, large file searches)
+- Multiple independent tasks can run in parallel (use `run_in_background=True`)
+- Exploring/researching codebase extensively with many file reads
+
+❌ DON'T use task when:
+- Task is straightforward → execute directly for better user visibility
+- Need user clarification → subagents cannot ask questions
+- Need real-time feedback → main agent has streaming, subagents don't
+- Task depends on conversation context → subagents have isolated context
+
+**Background Task Protocol (CRITICAL):**
+When you use `run_in_background=True`:
+1. **You MUST wait for completion** - Background tasks run asynchronously, but you are responsible for getting results
+2. **Poll task status** - Call `task_status(task_id)` to check progress
+3. **Check status field** - Status can be: `pending`, `running`, `completed`, `failed`
+4. **Retry if still running** - If status is `pending` or `running`, wait a moment and call `task_status` again
+5. **Report results to user** - Only respond to user AFTER getting the final result
+
+**STRICT RULE: Never end the conversation with background tasks still running. You MUST retrieve all results first.**
+
+**Usage:**
+```python
+# Synchronous - wait for result (preferred for most cases)
+task(
+    subagent_type="general-purpose",
+    prompt="Search all Python files for deprecated API usage and list them",
+    description="Find deprecated APIs"
+)
+
+# Background - run in parallel (MUST poll for results)
+task_id = task(
+    subagent_type="bash",
+    prompt="Run npm install && npm run build && npm test",
+    description="Build and test frontend",
+    run_in_background=True
+)
+# Extract task_id from the response
+# Then IMMEDIATELY start polling:
+while True:
+    status_result = task_status(task_id)
+    if "Status: completed" in status_result or "Status: failed" in status_result:
+        # Task finished, use the result
+        break
+    # Task still running, continue polling
+
+# Multiple parallel tasks
+task_id_1 = task(..., run_in_background=True)
+task_id_2 = task(..., run_in_background=True)
+# Poll BOTH tasks until complete before responding to user
+```
+</subagent_system>
+
 <working_directory existed="true">
 - User uploads: `/mnt/user-data/uploads` - Files uploaded by the user (automatically listed in context)
 - User workspace: `/mnt/user-data/workspace` - Working directory for temporary files
@@ -181,9 +242,7 @@ def _get_memory_context() -> str:
             return ""
 
         memory_data = get_memory_data()
-        memory_content = format_memory_for_injection(
-            memory_data, max_tokens=config.max_injection_tokens
-        )
+        memory_content = format_memory_for_injection(memory_data, max_tokens=config.max_injection_tokens)
 
         if not memory_content.strip():
             return ""
@@ -214,12 +273,7 @@ def apply_prompt_template() -> str:
     # Generate skills list XML with paths (path points to SKILL.md file)
     if skills:
         skill_items = "\n".join(
-            f"    <skill>\n"
-            f"        <name>{skill.name}</name>\n"
-            f"        <description>{skill.description}</description>\n"
-            f"        <location>{skill.get_container_file_path(container_base_path)}</location>\n"
-            f"    </skill>"
-            for skill in skills
+            f"    <skill>\n        <name>{skill.name}</name>\n        <description>{skill.description}</description>\n        <location>{skill.get_container_file_path(container_base_path)}</location>\n    </skill>" for skill in skills
         )
         skills_list = f"<available_skills>\n{skill_items}\n</available_skills>"
     else:

backend/src/agents/memory/updater.py

@@ -273,9 +273,7 @@ class MemoryUpdater:
         # Remove facts
         facts_to_remove = set(update_data.get("factsToRemove", []))
         if facts_to_remove:
-            current_memory["facts"] = [
-                f for f in current_memory.get("facts", []) if f.get("id") not in facts_to_remove
-            ]
+            current_memory["facts"] = [f for f in current_memory.get("facts", []) if f.get("id") not in facts_to_remove]
 
         # Add new facts
         new_facts = update_data.get("newFacts", [])
@@ -304,9 +302,7 @@ class MemoryUpdater:
         return current_memory
 
 
-def update_memory_from_conversation(
-    messages: list[Any], thread_id: str | None = None
-) -> bool:
+def update_memory_from_conversation(messages: list[Any], thread_id: str | None = None) -> bool:
     """Convenience function to update memory from a conversation.
 
     Args:

backend/src/agents/middlewares/uploads_middleware.py

@@ -151,8 +151,9 @@ class UploadsMiddleware(AgentMiddleware[UploadsMiddlewareState]):
             State updates including uploaded files list.
         """
         import logging
+
         logger = logging.getLogger(__name__)
-        
+
         thread_id = runtime.context.get("thread_id")
         if thread_id is None:
             return None
@@ -172,7 +173,7 @@ class UploadsMiddleware(AgentMiddleware[UploadsMiddlewareState]):
                     logger.info(f"Found previously shown files: {extracted}")
 
         logger.info(f"Total shown files from history: {shown_files}")
-        
+
         # List only newly uploaded files
         files = self._list_newly_uploaded_files(thread_id, shown_files)
         logger.info(f"Newly uploaded files to inject: {[f['filename'] for f in files]}")
@@ -189,7 +190,7 @@ class UploadsMiddleware(AgentMiddleware[UploadsMiddlewareState]):
 
         # Create files message and prepend to the last human message content
         files_message = self._create_files_message(files)
-        
+
         # Extract original content - handle both string and list formats
         original_content = ""
         if isinstance(last_message.content, str):
@@ -201,9 +202,9 @@ class UploadsMiddleware(AgentMiddleware[UploadsMiddlewareState]):
                 if isinstance(block, dict) and block.get("type") == "text":
                     text_parts.append(block.get("text", ""))
             original_content = "\n".join(text_parts)
-        
+
         logger.info(f"Original message content: {original_content[:100] if original_content else '(empty)'}")
-        
+
         # Create new message with combined content
         updated_message = HumanMessage(
             content=f"{files_message}\n\n{original_content}",