Files
deer-flow/backend/packages/harness/deerflow/agents/middlewares/loop_detection_middleware.py
T
Nan Gao dcc6f1e678 feat(loop-detection): defer warning injection (#2752)
* fix(loop-detection): defer warn injection to wrap_model_call

The warn branch in LoopDetectionMiddleware injected a HumanMessage
into state from after_model. The tools node had not yet produced
ToolMessage responses to the previous AIMessage(tool_calls=...), so
the new HumanMessage landed *between* the assistant's tool_calls and
their responses. OpenAI/Moonshot reject the next request with
"tool_call_ids did not have response messages" because their
validators require tool_calls to be followed immediately by tool
messages.

Detection now runs in after_model as before, but only enqueues the
warning into a per-thread list. Injection happens in wrap_model_call,
where every prior ToolMessage is already present in request.messages.
The warning is appended at the end as HumanMessage(name="loop_warning")
— pairing intact, AIMessage semantics untouched, no SystemMessage
issues for Anthropic.

Closes #2029, addresses #2255 #2293 #2304 #2511.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* fix(channels): remove loop warning display filter

* feat(loop-detection): scope pending warnings by run

* docs(loop-detection): update docs

* test(loop-detection): assert deferred warnings are queued

* fix(loop-detection): cap transient warning state

* docs: update docs

* add async awrap_model_call test coverage

* docs(loop-detection): document transient warnings

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>
2026-05-21 14:36:07 +08:00

613 lines
26 KiB
Python

"""Middleware to detect and break repetitive tool call loops.
P0 safety: prevents the agent from calling the same tool with the same
arguments indefinitely until the recursion limit kills the run.
Detection strategy:
1. After each model response, hash the tool calls (name + args).
2. Track recent hashes in a sliding window.
3. If the same hash appears >= warn_threshold times, queue a
"you are repeating yourself — wrap up" warning for the current
thread/run. The warning is **injected at the next model call** (in
``wrap_model_call``) as a ``HumanMessage`` appended to the message
list, *after* all ToolMessage responses to the previous
AIMessage(tool_calls).
4. If it appears >= hard_limit times, strip all tool_calls from the
response so the agent is forced to produce a final text answer.
Why the warning is injected at ``wrap_model_call`` instead of
``after_model``:
``after_model`` fires immediately after the model emits an
``AIMessage`` that may carry ``tool_calls``. The tools node has not
run yet, so no matching ``ToolMessage`` exists in the history. Any
message we add here lands *between* the assistant's tool_calls and
their responses. OpenAI/Moonshot reject the next request with
``"tool_call_ids did not have response messages"`` because their
validators require the assistant's tool_calls to be followed
immediately by tool messages. Anthropic also disallows mid-stream
``SystemMessage``. By deferring the warning to ``wrap_model_call``,
every prior ToolMessage is already present in the request's message
list and the warning is appended at the end — pairing intact, no
``AIMessage`` semantics are mutated.
Queued warnings are intentionally transient. If a run ends before the
next model request drains a queued warning, ``after_agent`` drops it
instead of carrying it into a later invocation for the same thread. The
hard-stop path still forces termination when the configured safety limit
is reached.
"""
from __future__ import annotations
import hashlib
import json
import logging
import threading
from collections import OrderedDict, defaultdict
from collections.abc import Awaitable, Callable
from copy import deepcopy
from typing import TYPE_CHECKING, override
from langchain.agents import AgentState
from langchain.agents.middleware import AgentMiddleware
from langchain.agents.middleware.types import ModelCallResult, ModelRequest, ModelResponse
from langchain_core.messages import HumanMessage
from langgraph.runtime import Runtime
if TYPE_CHECKING:
from deerflow.config.loop_detection_config import LoopDetectionConfig
logger = logging.getLogger(__name__)
# Defaults — can be overridden via constructor
_DEFAULT_WARN_THRESHOLD = 3 # inject warning after 3 identical calls
_DEFAULT_HARD_LIMIT = 5 # force-stop after 5 identical calls
_DEFAULT_WINDOW_SIZE = 20 # track last N tool calls
_DEFAULT_MAX_TRACKED_THREADS = 100 # LRU eviction limit
_DEFAULT_TOOL_FREQ_WARN = 30 # warn after 30 calls to the same tool type
_DEFAULT_TOOL_FREQ_HARD_LIMIT = 50 # force-stop after 50 calls to the same tool type
_MAX_PENDING_WARNINGS_PER_RUN = 4
def _normalize_tool_call_args(raw_args: object) -> tuple[dict, str | None]:
"""Normalize tool call args to a dict plus an optional fallback key.
Some providers serialize ``args`` as a JSON string instead of a dict.
We defensively parse those cases so loop detection does not crash while
still preserving a stable fallback key for non-dict payloads.
"""
if isinstance(raw_args, dict):
return raw_args, None
if isinstance(raw_args, str):
try:
parsed = json.loads(raw_args)
except (TypeError, ValueError, json.JSONDecodeError):
return {}, raw_args
if isinstance(parsed, dict):
return parsed, None
return {}, json.dumps(parsed, sort_keys=True, default=str)
if raw_args is None:
return {}, None
return {}, json.dumps(raw_args, sort_keys=True, default=str)
def _stable_tool_key(name: str, args: dict, fallback_key: str | None) -> str:
"""Derive a stable key from salient args without overfitting to noise."""
if name == "read_file" and fallback_key is None:
path = args.get("path") or ""
start_line = args.get("start_line")
end_line = args.get("end_line")
bucket_size = 200
try:
start_line = int(start_line) if start_line is not None else 1
except (TypeError, ValueError):
start_line = 1
try:
end_line = int(end_line) if end_line is not None else start_line
except (TypeError, ValueError):
end_line = start_line
start_line, end_line = sorted((start_line, end_line))
bucket_start = max(start_line, 1)
bucket_end = max(end_line, 1)
bucket_start = (bucket_start - 1) // bucket_size
bucket_end = (bucket_end - 1) // bucket_size
return f"{path}:{bucket_start}-{bucket_end}"
# write_file / str_replace are content-sensitive: same path may be updated
# with different payloads during iteration. Using only salient fields (path)
# can collapse distinct calls, so we hash full args to reduce false positives.
if name in {"write_file", "str_replace"}:
if fallback_key is not None:
return fallback_key
return json.dumps(args, sort_keys=True, default=str)
salient_fields = ("path", "url", "query", "command", "pattern", "glob", "cmd")
stable_args = {field: args[field] for field in salient_fields if args.get(field) is not None}
if stable_args:
return json.dumps(stable_args, sort_keys=True, default=str)
if fallback_key is not None:
return fallback_key
return json.dumps(args, sort_keys=True, default=str)
def _hash_tool_calls(tool_calls: list[dict]) -> str:
"""Deterministic hash of a set of tool calls (name + stable key).
This is intended to be order-independent: the same multiset of tool calls
should always produce the same hash, regardless of their input order.
"""
# Normalize each tool call to a stable (name, key) structure.
normalized: list[str] = []
for tc in tool_calls:
name = tc.get("name", "")
args, fallback_key = _normalize_tool_call_args(tc.get("args", {}))
key = _stable_tool_key(name, args, fallback_key)
normalized.append(f"{name}:{key}")
# Sort so permutations of the same multiset of calls yield the same ordering.
normalized.sort()
blob = json.dumps(normalized, sort_keys=True, default=str)
return hashlib.md5(blob.encode()).hexdigest()[:12]
_WARNING_MSG = "[LOOP DETECTED] You are repeating the same tool calls. Stop calling tools and produce your final answer now. If you cannot complete the task, summarize what you accomplished so far."
_TOOL_FREQ_WARNING_MSG = (
"[LOOP DETECTED] You have called {tool_name} {count} times without producing a final answer. Stop calling tools and produce your final answer now. If you cannot complete the task, summarize what you accomplished so far."
)
_HARD_STOP_MSG = "[FORCED STOP] Repeated tool calls exceeded the safety limit. Producing final answer with results collected so far."
_TOOL_FREQ_HARD_STOP_MSG = "[FORCED STOP] Tool {tool_name} called {count} times — exceeded the per-tool safety limit. Producing final answer with results collected so far."
class LoopDetectionMiddleware(AgentMiddleware[AgentState]):
"""Detects and breaks repetitive tool call loops.
Threshold parameters are validated upstream by :class:`LoopDetectionConfig`;
construct via :meth:`from_config` to ensure values pass Pydantic validation.
Args:
warn_threshold: Number of identical tool call sets before injecting
a warning message. Default: 3.
hard_limit: Number of identical tool call sets before stripping
tool_calls entirely. Default: 5.
window_size: Size of the sliding window for tracking calls.
Default: 20.
max_tracked_threads: Maximum number of threads to track before
evicting the least recently used. Default: 100.
tool_freq_warn: Number of calls to the same tool *type* (regardless
of arguments) before injecting a frequency warning. Catches
cross-file read loops that hash-based detection misses.
Default: 30.
tool_freq_hard_limit: Number of calls to the same tool type before
forcing a stop. Default: 50.
tool_freq_overrides: Per-tool overrides for frequency thresholds,
keyed by tool name. Each value is a ``(warn, hard_limit)`` tuple
that replaces ``tool_freq_warn`` / ``tool_freq_hard_limit`` for
that specific tool. Tools not listed here fall back to the global
thresholds. Useful for raising limits on intentionally
high-frequency tools (e.g. ``bash`` in batch pipelines) without
weakening protection on all other tools. Default: ``None``
(no overrides).
"""
def __init__(
self,
warn_threshold: int = _DEFAULT_WARN_THRESHOLD,
hard_limit: int = _DEFAULT_HARD_LIMIT,
window_size: int = _DEFAULT_WINDOW_SIZE,
max_tracked_threads: int = _DEFAULT_MAX_TRACKED_THREADS,
tool_freq_warn: int = _DEFAULT_TOOL_FREQ_WARN,
tool_freq_hard_limit: int = _DEFAULT_TOOL_FREQ_HARD_LIMIT,
tool_freq_overrides: dict[str, tuple[int, int]] | None = None,
):
super().__init__()
self.warn_threshold = warn_threshold
self.hard_limit = hard_limit
self.window_size = window_size
self.max_tracked_threads = max_tracked_threads
self.tool_freq_warn = tool_freq_warn
self.tool_freq_hard_limit = tool_freq_hard_limit
self._tool_freq_overrides: dict[str, tuple[int, int]] = tool_freq_overrides or {}
self._lock = threading.Lock()
self._history: OrderedDict[str, list[str]] = OrderedDict()
self._warned: dict[str, set[str]] = defaultdict(set)
self._tool_freq: dict[str, dict[str, int]] = defaultdict(lambda: defaultdict(int))
self._tool_freq_warned: dict[str, set[str]] = defaultdict(set)
# Per-thread/run queue of warnings to inject at the next model call.
# Populated by ``after_model`` (detection) and drained by
# ``wrap_model_call`` (injection); see module docstring.
self._pending_warnings: dict[tuple[str, str], list[str]] = defaultdict(list)
self._pending_warning_touch_order: OrderedDict[tuple[str, str], None] = OrderedDict()
self._max_pending_warning_keys = max(1, self.max_tracked_threads * 2)
@classmethod
def from_config(cls, config: LoopDetectionConfig) -> LoopDetectionMiddleware:
"""Construct from a Pydantic-validated config, trusting its validation."""
return cls(
warn_threshold=config.warn_threshold,
hard_limit=config.hard_limit,
window_size=config.window_size,
max_tracked_threads=config.max_tracked_threads,
tool_freq_warn=config.tool_freq_warn,
tool_freq_hard_limit=config.tool_freq_hard_limit,
tool_freq_overrides={name: (o.warn, o.hard_limit) for name, o in config.tool_freq_overrides.items()},
)
def _get_thread_id(self, runtime: Runtime) -> str:
"""Extract thread_id from runtime context for per-thread tracking."""
thread_id = runtime.context.get("thread_id") if runtime.context else None
if thread_id:
return str(thread_id)
return "default"
def _get_run_id(self, runtime: Runtime) -> str:
"""Extract run_id from runtime context for per-run warning scoping."""
run_id = runtime.context.get("run_id") if runtime.context else None
if run_id:
return str(run_id)
return "default"
def _pending_key(self, runtime: Runtime) -> tuple[str, str]:
"""Return the pending-warning key for the current thread/run."""
return self._get_thread_id(runtime), self._get_run_id(runtime)
def _evict_if_needed(self) -> None:
"""Evict least recently used threads if over the limit.
Must be called while holding self._lock.
"""
while len(self._history) > self.max_tracked_threads:
evicted_id, _ = self._history.popitem(last=False)
self._warned.pop(evicted_id, None)
self._tool_freq.pop(evicted_id, None)
self._tool_freq_warned.pop(evicted_id, None)
for key in list(self._pending_warnings):
if key[0] == evicted_id:
self._drop_pending_warning_key_locked(key)
logger.debug("Evicted loop tracking for thread %s (LRU)", evicted_id)
def _drop_pending_warning_key_locked(self, key: tuple[str, str]) -> None:
"""Drop all pending-warning bookkeeping for one thread/run key.
Must be called while holding self._lock.
"""
self._pending_warnings.pop(key, None)
self._pending_warning_touch_order.pop(key, None)
def _touch_pending_warning_key_locked(self, key: tuple[str, str]) -> None:
"""Mark a pending-warning key as recently used.
Must be called while holding self._lock.
"""
self._pending_warning_touch_order[key] = None
self._pending_warning_touch_order.move_to_end(key)
def _prune_pending_warning_state_locked(self, protected_key: tuple[str, str]) -> None:
"""Cap pending-warning state across abnormal or concurrent runs.
Must be called while holding self._lock.
"""
overflow = len(self._pending_warning_touch_order) - self._max_pending_warning_keys
if overflow <= 0:
return
candidates = [key for key in self._pending_warning_touch_order if key != protected_key]
for key in candidates[:overflow]:
self._drop_pending_warning_key_locked(key)
def _queue_pending_warning(self, runtime: Runtime, warning: str) -> None:
"""Queue one transient warning for the current thread/run with caps."""
pending_key = self._pending_key(runtime)
with self._lock:
warnings = self._pending_warnings[pending_key]
if warning not in warnings:
warnings.append(warning)
if len(warnings) > _MAX_PENDING_WARNINGS_PER_RUN:
del warnings[: len(warnings) - _MAX_PENDING_WARNINGS_PER_RUN]
self._touch_pending_warning_key_locked(pending_key)
self._prune_pending_warning_state_locked(protected_key=pending_key)
def _track_and_check(self, state: AgentState, runtime: Runtime) -> tuple[str | None, bool]:
"""Track tool calls and check for loops.
Two detection layers:
1. **Hash-based** (existing): catches identical tool call sets.
2. **Frequency-based** (new): catches the same *tool type* being
called many times with varying arguments (e.g. ``read_file``
on 40 different files).
Returns:
(warning_message_or_none, should_hard_stop)
"""
messages = state.get("messages", [])
if not messages:
return None, False
last_msg = messages[-1]
if getattr(last_msg, "type", None) != "ai":
return None, False
tool_calls = getattr(last_msg, "tool_calls", None)
if not tool_calls:
return None, False
thread_id = self._get_thread_id(runtime)
call_hash = _hash_tool_calls(tool_calls)
with self._lock:
# Touch / create entry (move to end for LRU)
if thread_id in self._history:
self._history.move_to_end(thread_id)
else:
self._history[thread_id] = []
self._evict_if_needed()
history = self._history[thread_id]
history.append(call_hash)
if len(history) > self.window_size:
history[:] = history[-self.window_size :]
warned_hashes = self._warned.get(thread_id)
if warned_hashes is not None:
warned_hashes.intersection_update(history)
if not warned_hashes:
self._warned.pop(thread_id, None)
count = history.count(call_hash)
tool_names = [tc.get("name", "?") for tc in tool_calls]
# --- Layer 1: hash-based (identical call sets) ---
if count >= self.hard_limit:
logger.error(
"Loop hard limit reached — forcing stop",
extra={
"thread_id": thread_id,
"call_hash": call_hash,
"count": count,
"tools": tool_names,
},
)
return _HARD_STOP_MSG, True
if count >= self.warn_threshold:
warned = self._warned[thread_id]
if call_hash not in warned:
warned.add(call_hash)
logger.warning(
"Repetitive tool calls detected — injecting warning",
extra={
"thread_id": thread_id,
"call_hash": call_hash,
"count": count,
"tools": tool_names,
},
)
return _WARNING_MSG, False
# --- Layer 2: per-tool-type frequency ---
freq = self._tool_freq[thread_id]
for tc in tool_calls:
name = tc.get("name", "")
if not name:
continue
freq[name] += 1
tc_count = freq[name]
if name in self._tool_freq_overrides:
eff_warn, eff_hard = self._tool_freq_overrides[name]
else:
eff_warn, eff_hard = self.tool_freq_warn, self.tool_freq_hard_limit
if tc_count >= eff_hard:
logger.error(
"Tool frequency hard limit reached — forcing stop",
extra={
"thread_id": thread_id,
"tool_name": name,
"count": tc_count,
},
)
return _TOOL_FREQ_HARD_STOP_MSG.format(tool_name=name, count=tc_count), True
if tc_count >= eff_warn:
warned = self._tool_freq_warned[thread_id]
if name not in warned:
warned.add(name)
logger.warning(
"Tool frequency warning — too many calls to same tool type",
extra={
"thread_id": thread_id,
"tool_name": name,
"count": tc_count,
},
)
return _TOOL_FREQ_WARNING_MSG.format(tool_name=name, count=tc_count), False
return None, False
@staticmethod
def _append_text(content: str | list | None, text: str) -> str | list:
"""Append *text* to AIMessage content, handling str, list, and None.
When content is a list of content blocks (e.g. Anthropic thinking mode),
we append a new ``{"type": "text", ...}`` block instead of concatenating
a string to a list, which would raise ``TypeError``.
"""
if content is None:
return text
if isinstance(content, list):
return [*content, {"type": "text", "text": f"\n\n{text}"}]
if isinstance(content, str):
return content + f"\n\n{text}"
# Fallback: coerce unexpected types to str to avoid TypeError
return str(content) + f"\n\n{text}"
@staticmethod
def _build_hard_stop_update(last_msg, content: str | list) -> dict:
"""Clear tool-call metadata so forced-stop messages serialize as plain assistant text."""
update = {
"tool_calls": [],
"content": content,
}
additional_kwargs = dict(getattr(last_msg, "additional_kwargs", {}) or {})
for key in ("tool_calls", "function_call"):
additional_kwargs.pop(key, None)
update["additional_kwargs"] = additional_kwargs
response_metadata = deepcopy(getattr(last_msg, "response_metadata", {}) or {})
if response_metadata.get("finish_reason") == "tool_calls":
response_metadata["finish_reason"] = "stop"
update["response_metadata"] = response_metadata
return update
def _apply(self, state: AgentState, runtime: Runtime) -> dict | None:
warning, hard_stop = self._track_and_check(state, runtime)
if hard_stop:
# Strip tool_calls from the last AIMessage to force text output.
# Once tool_calls are stripped, the AIMessage no longer requires
# matching ToolMessage responses, so mutating it in place here
# is safe for OpenAI/Moonshot pairing validators.
messages = state.get("messages", [])
last_msg = messages[-1]
content = self._append_text(last_msg.content, warning or _HARD_STOP_MSG)
stripped_msg = last_msg.model_copy(update=self._build_hard_stop_update(last_msg, content))
return {"messages": [stripped_msg]}
if warning:
# Defer injection to the next model call. We must NOT alter the
# AIMessage(tool_calls=...) here (would put framework words in
# the model's mouth, polluting downstream consumers like
# MemoryMiddleware), nor insert a separate non-tool message
# (would break OpenAI/Moonshot tool-call pairing because the
# tools node has not produced ToolMessage responses yet). The
# warning is delivered via ``wrap_model_call`` below.
self._queue_pending_warning(runtime, warning)
return None
return None
def _clear_other_run_pending_warnings(self, runtime: Runtime) -> None:
"""Drop stale pending warnings for previous runs in this thread."""
thread_id, current_run_id = self._pending_key(runtime)
with self._lock:
for key in list(self._pending_warnings):
if key[0] == thread_id and key[1] != current_run_id:
self._drop_pending_warning_key_locked(key)
def _clear_current_run_pending_warnings(self, runtime: Runtime) -> None:
"""Drop pending warnings owned by the current thread/run."""
pending_key = self._pending_key(runtime)
with self._lock:
self._drop_pending_warning_key_locked(pending_key)
@staticmethod
def _format_warning_message(warnings: list[str]) -> str:
"""Merge pending warnings into one prompt message."""
deduped = list(dict.fromkeys(warnings))
return "\n\n".join(deduped)
@override
def before_agent(self, state: AgentState, runtime: Runtime) -> dict | None:
self._clear_other_run_pending_warnings(runtime)
return None
@override
async def abefore_agent(self, state: AgentState, runtime: Runtime) -> dict | None:
self._clear_other_run_pending_warnings(runtime)
return None
@override
def after_model(self, state: AgentState, runtime: Runtime) -> dict | None:
return self._apply(state, runtime)
@override
async def aafter_model(self, state: AgentState, runtime: Runtime) -> dict | None:
return self._apply(state, runtime)
@override
def after_agent(self, state: AgentState, runtime: Runtime) -> dict | None:
self._clear_current_run_pending_warnings(runtime)
return None
@override
async def aafter_agent(self, state: AgentState, runtime: Runtime) -> dict | None:
self._clear_current_run_pending_warnings(runtime)
return None
def _drain_pending_warnings(self, runtime: Runtime) -> list[str]:
"""Pop and return all queued warnings for *runtime*'s thread/run."""
pending_key = self._pending_key(runtime)
with self._lock:
warnings = self._pending_warnings.pop(pending_key, [])
self._pending_warning_touch_order.pop(pending_key, None)
return warnings
def _augment_request(self, request: ModelRequest) -> ModelRequest:
"""Append queued loop warnings (if any) to the outgoing message list.
The warning is placed *after* every existing message, including the
ToolMessage responses to the previous AIMessage(tool_calls). This
keeps ``assistant tool_calls -> tool_messages`` pairing intact for
OpenAI/Moonshot, avoids the Anthropic mid-stream SystemMessage
restriction (we use HumanMessage), and never mutates an existing
AIMessage.
"""
warnings = self._drain_pending_warnings(request.runtime)
if not warnings:
return request
new_messages = [
*request.messages,
HumanMessage(content=self._format_warning_message(warnings), name="loop_warning"),
]
return request.override(messages=new_messages)
@override
def wrap_model_call(
self,
request: ModelRequest,
handler: Callable[[ModelRequest], ModelResponse],
) -> ModelCallResult:
return handler(self._augment_request(request))
@override
async def awrap_model_call(
self,
request: ModelRequest,
handler: Callable[[ModelRequest], Awaitable[ModelResponse]],
) -> ModelCallResult:
return await handler(self._augment_request(request))
def reset(self, thread_id: str | None = None) -> None:
"""Clear tracking state. If thread_id given, clear only that thread."""
with self._lock:
if thread_id:
self._history.pop(thread_id, None)
self._warned.pop(thread_id, None)
self._tool_freq.pop(thread_id, None)
self._tool_freq_warned.pop(thread_id, None)
for key in list(self._pending_warnings):
if key[0] == thread_id:
self._drop_pending_warning_key_locked(key)
else:
self._history.clear()
self._warned.clear()
self._tool_freq.clear()
self._tool_freq_warned.clear()
self._pending_warnings.clear()
self._pending_warning_touch_order.clear()