diff --git a/README.md b/README.md
index 2aa33ce5aa..8ffbd9926e 100644
--- a/README.md
+++ b/README.md
@@ -2985,6 +2985,8 @@ Each task gets its own execution environment with a full filesystem view — ski
 
 The read-before-write gate ties each read mark to that `read_file` call's result, including custom tools returning multi-message `Command` updates. An unrelated result cannot authorize a write after a failed read or hide a successful read.
 
+Deeply nested JSON returned by tools, including `read_file`, keeps its original content when result analysis reaches the JSON parser's depth limit. Explicit tool failures remain errors with an unknown category when depth prevents analysis.
+
 On Linux and macOS, local sandbox `write_file` replacements and `str_replace` stage complete text before replacing the destination, so write, flush or publication errors retain the previous file. Existing write access is checked; ownership, permission bits, ACLs and extended attributes are transferred before writing staging content. Failure to transfer metadata aborts the save. Successful revisions get a fresh modification time, including empty saves; source-descriptor cleanup errors are warnings and do not change the save result. Files with set-id bits, macOS file flags or content-bound Linux privilege attributes are refused unchanged. Replacement requires parent-directory write access and publishes a new inode; other hard links retain the previous version. Symlinks follow the existing path-validation rules. Append writes, other host platforms (including Windows), shell writes and remote providers keep their existing behavior. This is not a concurrent-writer or power-loss recovery guarantee.
 
 Loop warnings let agents save collected results before their final answer. If the save is blocked by the read-before-write gate, the agent may read the target file and retry the save once. A looping or stopped tool must be replaced by an available alternative; if no permitted save path exists or the retry fails, the final answer includes the collected results and reports that the file was not saved. When `present_files` is available, the warning also asks the agent to present the files it already created in `/mnt/user-data/outputs` before answering, so finished outputs are delivered. Recovery calls still count toward the loop limits, and a hard stop prevents further tool execution.
diff --git a/backend/packages/harness/deerflow/agents/middlewares/AGENTS.md b/backend/packages/harness/deerflow/agents/middlewares/AGENTS.md
index 11802329c8..10cd14bead 100644
--- a/backend/packages/harness/deerflow/agents/middlewares/AGENTS.md
+++ b/backend/packages/harness/deerflow/agents/middlewares/AGENTS.md
@@ -1,5 +1,13 @@
 ### Middleware Chain
 
+Tool-result JSON analysis is best-effort: parser depth failures must preserve the
+original content and must not abort the graph. Explicit error results fall back
+to `unknown` / recoverable / `try_alternative`, without classifying incidental
+JSON fields as auth failures. Producer metadata remains authoritative. Keep
+depth regressions in `tests/test_tool_result_meta_json_depth.py`, including real
+LocalSandbox reads through both synchronous and asynchronous agent graphs.
+Deep graph cases must establish a real parser depth failure or report a skip.
+
 Async gate waiters own separate cross-loop futures. Cancel only their signal;
 notify outside the state lock. `_await_off_thread` drains started I/O across
 repeated cancellation.
diff --git a/backend/packages/harness/deerflow/agents/middlewares/tool_result_meta.py b/backend/packages/harness/deerflow/agents/middlewares/tool_result_meta.py
index 7dc34c1362..1ad0959539 100644
--- a/backend/packages/harness/deerflow/agents/middlewares/tool_result_meta.py
+++ b/backend/packages/harness/deerflow/agents/middlewares/tool_result_meta.py
@@ -156,7 +156,7 @@ def _extract_json_error_text(content: str) -> str | None:
     """
     try:
         data = json.loads(content)
-    except (json.JSONDecodeError, ValueError):
+    except (json.JSONDecodeError, ValueError, RecursionError):
         return None
     error = data.get("error") if isinstance(data, dict) else None
     if not error:
@@ -305,9 +305,14 @@ def normalize_tool_message(msg: ToolMessage) -> ToolMessage:
             # the tool.  Classify raw text only when the content is not valid JSON.
             try:
                 is_json_dict = isinstance(json.loads(content), dict)
+            except RecursionError:
+                # Depth-limited analysis cannot establish an error category.
+                # Do not infer auth/stop from incidental fields in the raw JSON.
+                attrs = {**_UNKNOWN_ERROR}
             except (json.JSONDecodeError, ValueError):
-                is_json_dict = False
-            attrs = {**_UNKNOWN_ERROR} if is_json_dict else _classify_error_text(content)
+                attrs = _classify_error_text(content)
+            else:
+                attrs = {**_UNKNOWN_ERROR} if is_json_dict else _classify_error_text(content)
         meta = _make_meta(status="error", source="tool_return", **attrs)
     elif content.startswith(_ERROR_PREFIX):
         attrs = _classify_error_text(content[len(_ERROR_PREFIX) :])
diff --git a/backend/tests/test_tool_result_meta_json_depth.py b/backend/tests/test_tool_result_meta_json_depth.py
new file mode 100644
index 0000000000..1fa8735a24
--- /dev/null
+++ b/backend/tests/test_tool_result_meta_json_depth.py
@@ -0,0 +1,120 @@
+"""JSON depth limits must not replace successful native tool results."""
+
+import json
+from unittest.mock import AsyncMock, Mock
+
+import pytest
+from langchain.agents import create_agent
+from langchain_core.language_models.fake_chat_models import GenericFakeChatModel
+from langchain_core.messages import AIMessage, HumanMessage, ToolMessage
+
+from deerflow.agents.middlewares import tool_result_meta as meta
+from deerflow.agents.middlewares.tool_error_handling_middleware import ToolErrorHandlingMiddleware
+from deerflow.agents.middlewares.tool_receipt import TOOL_RECEIPT_KEY
+from deerflow.agents.middlewares.tool_receipt_middleware import ToolReceiptMiddleware
+from deerflow.agents.thread_state import ThreadState
+
+
+@pytest.mark.parametrize("status", ["success", "error"])
+def test_json_depth_limit_preserves_result(monkeypatch, status):
+    content = '{"records": [[[0]]], "user_id": 401}'
+    loads = Mock(side_effect=RecursionError("parser depth limit"))
+    monkeypatch.setattr(meta.json, "loads", loads)
+    message = ToolMessage(content=content, name="custom_tool", tool_call_id="depth", status=status)
+
+    result = meta.normalize_tool_message(message)
+
+    assert result is message
+    assert result.content == content
+    assert result.tool_call_id == "depth"
+    assert result.status == status
+    assert result.additional_kwargs[meta.TOOL_META_KEY] == {
+        "status": status,
+        "error_type": "unknown" if status == "error" else None,
+        "recoverable_by_model": True,
+        "recommended_next_action": "try_alternative" if status == "error" else "continue",
+        "source": "tool_return" if status == "error" else "content_analysis",
+    }
+    assert loads.call_count == (2 if status == "error" else 1)
+
+
+def test_second_json_probe_depth_limit_is_unknown(monkeypatch):
+    loads = Mock(side_effect=[{}, RecursionError("parser depth limit")])
+    monkeypatch.setattr(meta.json, "loads", loads)
+    message = ToolMessage(content='{"user_id": 401}', tool_call_id="depth", status="error")
+
+    result = meta.normalize_tool_message(message)
+
+    assert loads.call_count == 2
+    assert result.status == "error"
+    assert result.additional_kwargs[meta.TOOL_META_KEY]["error_type"] == "unknown"
+    assert result.additional_kwargs[meta.TOOL_META_KEY]["recommended_next_action"] == "try_alternative"
+
+
+def test_producer_metadata_bypasses_depth_analysis(monkeypatch):
+    loads = Mock(side_effect=RecursionError("parser depth limit"))
+    monkeypatch.setattr(meta.json, "loads", loads)
+    stamp = {"status": "error", "error_type": "auth", "source": "tool_return"}
+    message = ToolMessage(content="[0]", tool_call_id="depth", additional_kwargs={meta.TOOL_META_KEY: stamp})
+
+    assert meta.normalize_tool_message(message).additional_kwargs[meta.TOOL_META_KEY] is stamp
+    loads.assert_not_called()
+
+
+@pytest.mark.parametrize("name,expected", [("custom_tool", "error"), ("read_file", "success")])
+def test_shallow_error_envelope_classification(name, expected):
+    message = ToolMessage(content='{"error": {"code": 401}}', name=name, tool_call_id="shallow")
+    result = meta.normalize_tool_message(message)
+    assert result.additional_kwargs[meta.TOOL_META_KEY]["status"] == expected
+    assert result.additional_kwargs[meta.TOOL_META_KEY]["error_type"] == ("auth" if expected == "error" else None)
+
+
+class _ScriptedModel(GenericFakeChatModel):
+    def bind_tools(self, tools, **kwargs):
+        return self
+
+
+@pytest.mark.parametrize("mode", ["sync", "async"])
+@pytest.mark.parametrize("depth", [10, 10000])
+@pytest.mark.asyncio
+async def test_native_read_file_graph_preserves_deep_json(tmp_path, monkeypatch, mode, depth):
+    from deerflow.sandbox import tools as sandbox_tools
+    from deerflow.sandbox.local.local_sandbox import LocalSandbox
+
+    # String construction avoids recursive Python fixtures. Count the deep case
+    # as regression coverage only when the real parser rejects this fixture.
+    content = "[" * depth + "0" + "]" * depth
+    if depth > 10:
+        try:
+            json.loads(content)
+        except RecursionError:
+            pass
+        else:
+            pytest.skip(f"json.loads accepts {depth} nested arrays; parser depth limit is not exercised")
+    path = tmp_path / "nested.json"
+    path.write_text(content, encoding="utf-8")
+    sandbox = LocalSandbox("json-depth-test")
+    monkeypatch.setattr(sandbox_tools, "ensure_sandbox_initialized", lambda *_args, **_kwargs: sandbox)
+    monkeypatch.setattr(sandbox_tools, "ensure_sandbox_initialized_async", AsyncMock(return_value=sandbox))
+    responses = [AIMessage(content="", tool_calls=[{"name": "read_file", "args": {"path": str(path)}, "id": "read-depth"}]), AIMessage(content="Done.")]
+    graph = create_agent(
+        _ScriptedModel(messages=iter(responses)),
+        tools=[sandbox_tools.read_file_tool],
+        middleware=[ToolReceiptMiddleware(render_mode="delegation_only"), ToolErrorHandlingMiddleware()],
+        state_schema=ThreadState,
+    )
+    state = {
+        "messages": [HumanMessage(content="Read the JSON file.")],
+        "sandbox": {"sandbox_id": "json-depth-test"},
+        "thread_data": {"outputs_path": str(tmp_path)},
+        "thread_directories_created": True,
+    }
+    context = {"thread_id": "json-depth-test", "user_id": "default"}
+    result = graph.invoke(state, context=context) if mode == "sync" else await graph.ainvoke(state, context=context)
+    message = next(message for message in result["messages"] if isinstance(message, ToolMessage))
+    assert message.content == content
+    assert message.tool_call_id == "read-depth"
+    assert message.status == "success"
+    assert message.additional_kwargs[meta.TOOL_META_KEY]["status"] == "success"
+    assert message.additional_kwargs[TOOL_RECEIPT_KEY]["status"] == "success"
+    assert result["messages"][-1].content == "Done."