feat(api): scoped read_project_folder_file tool with traversal guard

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/agents/folder_agent.py

@@ -0,0 +1,37 @@
+"""Scoped file-read tool for the project folder feature."""
+from __future__ import annotations
+
+from langchain_core.tools import tool
+
+from app.core.ws_context import execute_on_client
+
+
+def _is_unsafe_path(rel: str) -> bool:
+    if not rel:
+        return True
+    norm = rel.replace("\\", "/")
+    if norm.startswith("/"):
+        return True
+    # Windows drive letter
+    if len(rel) >= 2 and rel[1] == ":":
+        return True
+    parts = norm.split("/")
+    return ".." in parts
+
+
+@tool
+async def read_project_folder_file(project_id: str, relative_path: str) -> str:
+    """Read full content of a file inside the project's linked folder."""
+    if _is_unsafe_path(relative_path):
+        return "Access denied"
+    result = await execute_on_client(
+        action="read_project_folder_file",
+        data={"projectId": project_id, "relativePath": relative_path},
+    )
+    content = result.get("content", "")
+    if not content:
+        return f"File not found: {relative_path}"
+    return content
+
+
+FOLDER_TOOLS = [read_project_folder_file]