feat(agent): add custom-agent self-updates with user isolation (#2713)

* feat(agent): add update_agent tool for in-chat custom-agent self-updates (#2616)

Custom agents had no built-in way to persist updates to their own SOUL.md /
config.yaml from a normal chat — `setup_agent` was only bound during the
bootstrap flow, so when the user asked the agent to refine its description
or personality, the agent would shell out via bash/write_file and the edits
landed in a temporary sandbox/tool workspace instead of
`{base_dir}/agents/{agent_name}/`.

Changes:
- New `update_agent` builtin tool with partial-update semantics (only the
  fields you pass are written) and atomic temp-file + os.replace writes so
  a failed update never corrupts existing SOUL.md / config.yaml.
- Lead agent now binds `update_agent` in the non-bootstrap path whenever
  `agent_name` is set in the runtime context. Default agent (no
  agent_name) and bootstrap flow are unchanged.
- New `<self_update>` system-prompt section is injected for custom agents,
  instructing them to use `update_agent` — and explicitly NOT bash /
  write_file — to persist self-updates.
- Tests: 11 new cases in `tests/test_update_agent_tool.py` covering
  validation (missing/invalid agent_name, unknown agent, no fields),
  partial updates (soul-only, description-only, skills=[] vs omitted),
  no-op detection, atomic-write safety, and AgentConfig round-tripping;
  plus 2 new cases in `tests/test_lead_agent_prompt.py` covering the
  self-update prompt section.
- Docs: updated backend/CLAUDE.md builtin tools list and tools.mdx
  (en/zh) with the new tool description.

* feat(agent): isolate custom agents per user

Store custom agent definitions under the effective user, keep legacy agents readable until migration, and cover API/tool/migration behavior with tests.

Co-authored-by: Cursor <cursoragent@cursor.com>

* feat: consistent write/delete targets & add --user-id to migration

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/packages/harness/deerflow/agents/lead_agent/prompt.py

@@ -344,6 +344,7 @@ You are {agent_name}, an open-source super agent.
 </role>
 
 {soul}
+{self_update_section}
 {memory_context}
 
 <thinking_style>
@@ -643,6 +644,26 @@ def get_agent_soul(agent_name: str | None) -> str:
     return ""
 
 
+def _build_self_update_section(agent_name: str | None) -> str:
+    """Prompt block that teaches the custom agent to persist self-updates via update_agent."""
+    if not agent_name:
+        return ""
+    return f"""<self_update>
+You are running as the custom agent **{agent_name}** with a persisted SOUL.md and config.yaml.
+
+When the user asks you to update your own description, personality, behaviour, skill set, tool groups, or default model,
+you MUST persist the change with the `update_agent` tool. Do NOT use `bash`, `write_file`, or any sandbox tool to edit
+SOUL.md or config.yaml — those write into a temporary sandbox/tool workspace and the changes will be lost on the next turn.
+
+Rules:
+- Always pass the FULL replacement text for `soul` (no patch semantics). Start from your current SOUL above and apply the user's edits.
+- Only pass the fields that should change. Omit the others to preserve them.
+- Pass `skills=[]` to disable all skills, or omit `skills` to keep the existing whitelist.
+- After `update_agent` returns successfully, tell the user the change is persisted and will take effect on the next turn.
+</self_update>
+"""
+
+
 def get_deferred_tools_prompt_section(*, app_config: AppConfig | None = None) -> str:
     """Generate <available-deferred-tools> block for the system prompt.
 
@@ -772,6 +793,7 @@ def apply_prompt_template(
     prompt = SYSTEM_PROMPT_TEMPLATE.format(
         agent_name=agent_name or "DeerFlow 2.0",
         soul=get_agent_soul(agent_name),
+        self_update_section=_build_self_update_section(agent_name),
         skills_section=skills_section,
         deferred_tools_section=deferred_tools_section,
         memory_context=memory_context,