dsh-loop-detector

Dead-loop / repetition detector plugin for DeepSeek Harness (dsh).

Local LLMs (especially quantized / RL-tuned reasoning models) sometimes get stuck:
repeating the same sentence forever, or re-running web_search with reworded queries
for the same topic without gaining any new information. This plugin watches the
agent's stream in real time, detects both kinds of loops, and interrupts them
hard — not a soft reminder the model can ignore.

中文文档见 README.zh.md.

Features

• Text-level repetition detection — watches assistant/chunk (text-delta +
  optional reasoning-delta) with three layered detectors:
  1. Period scan: tail repeats with a fixed period (8–256 chars)
  2. n-gram: a 64-char block seen ≥3 times in the recent window
  3. Large-scale anchor: a 512-char tail block reappearing earlier (catches
     whole-paragraph repetition, e.g. a model re-planning the same answer twice)
• Tool-call intent-level repetition detection — watches tools/execute for
  web_search: extracts query keywords, keeps a "topic set" (union of the last 3
  queries), and if a new query brings <25% novel tokens twice in a row, it
  judges the model is re-searching the same topic with different wording
  (intent-level loop, invisible to plain string matching).
• Hard interrupt: on hit, agent.steer() injects a guidance message (auto
  retry, configurable); when retries are exhausted, agent.cancel() forcibly
  aborts the turn. Counters reset on turn/end.

Why hard interrupt? dsh's built-in repeat-tool-reminder only reminds the model.
We observed local models (e.g. Qwen/Ornith 35B MoE with thinking off) ignore the
reminder and keep looping — that's what this plugin exists for.

Quick start

Prereqs: a running dsh profile (see deepseek-harness docs).

Option A (recommended): install from npm (published to npm registry)

dsh plugin --profile web add dsh-loop-detector
dsh web   # restart to activate

Option B: install from a local copy

cp -r dsh-loop-detector $env:USERPROFILE\.dsh\profiles\web\node_modules\dsh-loop-detector

Then, in both cases, mount it via your profile's permanent patch layer
($env:USERPROFILE\.dsh\profiles\web\cordis.patch.yml):

- insert:
    - id: loop-detector
      name: 'dsh-loop-detector'
      config:
        minLen: 512          # only check output >= 512 chars (avoid short-text false positives)
        maxRetries: 1        # auto-retry 1x via steer; cancel when exhausted
        checkReasoning: true # also check reasoning-delta (thinking content)

Restart and verify:

dsh web

You should see the plugin loaded; when a loop is caught, the log shows:

[loop-detector] session xxx 检测到死循环（1/1）: large-scale repeat: ...；steer 引导重试
[loop-detector] session xxx 连续 2 次搜索同一主题（无新信息）: "..."；steer 引导停止搜索

A ready-to-use cordis.patch.yml example is included in this repo.

Configuration

How the detectors work

Text-level (detectRepetition)

1) period scan     tail 4 periods identical, period T in [8..256]        -> loop
2) n-gram          64-char block seen >= 3x in last 2048 chars           -> loop
3) large anchor    512-char tail block reappears earlier, extends >=512  -> loop

Tool-call intent-level

topic set = union of keywords of the last 3 web_search queries
new query  -> novel ratio = (# tokens not in topic set) / total tokens
novel ratio < 25% twice in a row  -> intent-level repetition -> steer/cancel

Verified against real cases: a Qwen3.5-9B stuck on an 82-char sentence
(period=132 caught), a 2120-char duplicated planning block caught, and an
11-query same-topic search streak caught at query #8 (no false positive on the
first 7 queries that each introduced new dimensions).

Scope & limitations

• Intent-level detection currently targets web_search; other tools can be
  added by extending the exec.name filter.
• The detectors are heuristic — tune minLen / thresholds for your model.
• Detection is per-session and resets on turn/end (no cross-turn carryover).

License

MIT — see LICENSE.