diff --git a/backend/agents/workspace_manager.py b/backend/agents/workspace_manager.py
index 57509fc..8a36d4c 100644
--- a/backend/agents/workspace_manager.py
+++ b/backend/agents/workspace_manager.py
@@ -129,6 +129,33 @@ class RunWorkspaceManager:
         )
         return asset_dir
 
+    def load_agent_file(
+        self,
+        *,
+        config_name: str,
+        agent_id: str,
+        filename: str,
+    ) -> str:
+        """Load one run-scoped agent workspace file."""
+        path = self.get_agent_asset_dir(config_name, agent_id) / filename
+        if not path.exists():
+            raise FileNotFoundError(f"File not found: {filename}")
+        return path.read_text(encoding="utf-8")
+
+    def update_agent_file(
+        self,
+        *,
+        config_name: str,
+        agent_id: str,
+        filename: str,
+        content: str,
+    ) -> None:
+        """Write one run-scoped agent workspace file."""
+        asset_dir = self.get_agent_asset_dir(config_name, agent_id)
+        asset_dir.mkdir(parents=True, exist_ok=True)
+        path = asset_dir / filename
+        path.write_text(content, encoding="utf-8")
+
     def initialize_default_assets(
         self,
         config_name: str,
diff --git a/backend/api/agents.py b/backend/api/agents.py
index 2633f5c..07a7209 100644
--- a/backend/api/agents.py
+++ b/backend/api/agents.py
@@ -13,7 +13,8 @@ from typing import Any, Dict, List, Optional
 from fastapi import APIRouter, HTTPException, Depends, Body, UploadFile, File, Form
 from pydantic import BaseModel, Field
 
-from backend.agents import AgentFactory, WorkspaceManager, get_registry
+from backend.agents import AgentFactory, get_registry
+from backend.agents.workspace_manager import RunWorkspaceManager
 from backend.agents.agent_workspace import load_agent_workspace_config
 from backend.agents.skills_manager import SkillsManager
 from backend.agents.toolkit_factory import load_agent_profiles
@@ -100,8 +101,8 @@ def get_agent_factory():
 
 
 def get_workspace_manager():
-    """Get WorkspaceManager instance."""
-    return WorkspaceManager()
+    """Get run-scoped workspace manager instance."""
+    return RunWorkspaceManager()
 
 
 def get_skills_manager():
@@ -652,7 +653,7 @@ async def get_agent_file(
     workspace_id: str,
     agent_id: str,
     filename: str,
-    workspace_manager: WorkspaceManager = Depends(get_workspace_manager),
+    workspace_manager: RunWorkspaceManager = Depends(get_workspace_manager),
 ):
     """
     Read an agent's workspace file.
@@ -682,7 +683,7 @@ async def update_agent_file(
     agent_id: str,
     filename: str,
     content: str = Body(..., media_type="text/plain"),
-    workspace_manager: WorkspaceManager = Depends(get_workspace_manager),
+    workspace_manager: RunWorkspaceManager = Depends(get_workspace_manager),
 ):
     """
     Update an agent's workspace file.