feat(v1): T-R3 采纳 llmrouter 词边界与失败安全——难度英文标记整词命中 + HF 分类器两级回落

- difficulty：标记表编译拆分——英文标记改词边界正则（修真实误判：'int' 子串
  命中 'print'/'point'、'log' 命中 'logic'、'list' 命中 'listen'），中文标记
  保持子串语义；命中行为对合法用例不变（整词出现照常计数）
- classifier：HuggingFaceClassifier 推理期异常回落内置 RuleClassifier（单次
  推理异常不打垮路由）；build_classifier 的 hf 分支构造失败（ML 依赖缺失/
  模型加载失败）打印提示并回落规则分类器（外置规则照常合并）
- 新增 tests/test_failsafe.py 5 项；全量 43 passed（38+5）

router_system/classifier.py

@@ -214,6 +214,8 @@ class HuggingFaceClassifier(BaseClassifier):
     """可选：基于 transformers 的序列分类模型。
 
     仅当安装 torch+transformers 且模型可加载时可用；否则抛错提示。
+    失败安全（T-R3，采纳 llmrouter 分类失败静默降级思想）：模型加载成功但
+    推理期异常时，自动回落内置规则分类器，不让单次推理异常打垮路由。
     """
 
     def __init__(self, model_name: str, num_labels: int = 5, confidence_floor: float = 0.55):
@@ -229,8 +231,10 @@ class HuggingFaceClassifier(BaseClassifier):
         )
         self.labels = ["code", "math", "legal", "medical", "general"]
         self.confidence_floor = confidence_floor
+        self._rule_fallback = RuleClassifier(confidence_floor=confidence_floor)
 
     def classify(self, query: str) -> Classification:
+        try:
             import torch  # type: ignore
 
             inputs = self.tokenizer(query, return_tensors="pt", truncation=True, max_length=256)
@@ -246,6 +250,8 @@ class HuggingFaceClassifier(BaseClassifier):
                 difficulty_score=ds,
                 raw_scores={self.labels[i]: round(float(probs[i]), 3) for i in range(len(self.labels))},
             )
+        except Exception:  # noqa: BLE001  推理失败回落规则分类器（失败安全）
+            return self._rule_fallback.classify(query)
 
 
 def build_classifier(cfg: Dict) -> BaseClassifier:
@@ -265,6 +271,18 @@ def build_classifier(cfg: Dict) -> BaseClassifier:
             clf.rules = {**DOMAIN_RULES, **external}
         return clf
     if ctype == "hf":
-        return HuggingFaceClassifier(cfg.get("model", "Qwen/Qwen3-0.6B"), confidence_floor=floor)
+        # 失败安全（T-R3）：ML 依赖缺失 / 模型加载失败时回落规则分类器
+        try:
+            return HuggingFaceClassifier(
+                cfg.get("model", "Qwen/Qwen3-0.6B"), confidence_floor=floor)
+        except Exception as e:  # noqa: BLE001
+            print(f"[classifier] HF 分类器不可用（{type(e).__name__}），回落规则分类器")
+            clf = RuleClassifier(confidence_floor=floor)
+            rules_file = cfg.get("rules_file")
+            external = load_domain_rules(rules_file) if rules_file \
+                else (load_domain_rules() if DEFAULT_RULES_FILE.exists() else None)
+            if external:
+                clf.rules = {**DOMAIN_RULES, **external}
+            return clf
     raise ValueError(f"未知分类器类型: {ctype}（支持 rule | hf）")
 

router_system/difficulty.py

@@ -25,16 +25,43 @@ _MEDIUM_MARKERS = [
     "translate", "fix", "explain", "describe", "list",
 ]
 
+
+def _compile_markers(markers):
+    """标记表编译：英文标记用词边界正则，中文标记保持子串匹配。
+
+    T-R3（采纳 llmrouter 词边界思想，super_hard 先于 hard 的同理）：
+    纯子串匹配会让 "int" 误命中 "print"/"point"、"log" 误命中 "logic"、
+    "list" 误命中 "listen"——英文必须整词命中才计数。
+    """
+    substr, words = [], []
+    for m in markers:
+        (words if m.isascii() else substr).append(m)
+    pattern = re.compile(r"\b(?:%s)\b" % "|".join(re.escape(w) for w in words)) \
+        if words else None
+    return substr, pattern
+
+
+_HARD_SUBSTR, _HARD_RE = _compile_markers(_HARD_MARKERS)
+_MEDIUM_SUBSTR, _MEDIUM_RE = _compile_markers(_MEDIUM_MARKERS)
+
 # 预编译正则（模块级一次，避免每次调用走 re 内部缓存查找）
 _RE_CODE_EXPR = re.compile(r"\b(def|class|function|import)\b")
 _RE_ARITH_EXPR = re.compile(r"[0-9]+\s*[+\-*/^=]\s*[0-9xya-z]")
 
 
+def _hit_count(substr, pattern, q: str) -> int:
+    """中文子串命中数 + 英文整词命中数。"""
+    n = sum(1 for m in substr if m in q)
+    if pattern is not None:
+        n += len(pattern.findall(q))
+    return n
+
+
 def estimate_difficulty(query: str) -> Tuple[str, float]:
     """返回 (difficulty, score)，score 属于 [0,1]。"""
     q = query.lower()
-    hard_hits = sum(1 for m in _HARD_MARKERS if m in q)
+    hard_hits = _hit_count(_HARD_SUBSTR, _HARD_RE, q)
-    medium_hits = sum(1 for m in _MEDIUM_MARKERS if m in q)
+    medium_hits = _hit_count(_MEDIUM_SUBSTR, _MEDIUM_RE, q)
     length = len(query)
 
     score = 0.0

tests/test_failsafe.py

@@ -0,0 +1,48 @@
+"""失败安全与词边界单元测试（T-R3，采纳 llmrouter 设计）。"""
+from router_system.classifier import RuleClassifier, build_classifier
+from router_system.difficulty import estimate_difficulty
+
+
+def test_word_boundary_stops_substring_false_positive():
+    """英文标记整词命中：'int' 不再被 'print'/'point' 误触发 hard。"""
+    diff, score = estimate_difficulty("如何用 print 函数打印结果")
+    # 旧实现 'int' 误命中 print 叠加 如何 -> hard；现在应为 medium 以下
+    assert diff in ("easy", "medium")
+
+    diff2, _ = estimate_difficulty("请总结这段逻辑代码的思路")
+    # 'sum' 不被 'summary/总结' 类场景误判：'逻辑' 含 'log' 也不再整词误命中
+    assert diff2 in ("easy", "medium")
+
+
+def test_word_boundary_still_counts_whole_words():
+    """整词出现照常计数：int/log 作为真词仍触发 hard 信号。"""
+    diff, _ = estimate_difficulty("explain how to implement int overflow and log parsing in depth")
+    assert diff in ("medium", "hard")
+
+
+def test_chinese_markers_keep_substring_semantics():
+    """中文标记保持子串语义：'证明' 命中 '证明费马大定理'。"""
+    diff, _ = estimate_difficulty("证明费马大定理并推导其推论，给出详细步骤")
+    assert diff in ("medium", "hard")
+
+
+def test_build_hf_falls_back_when_unavailable(monkeypatch):
+    """HF 分类器构造失败（依赖缺失/模型加载失败）安全回落规则分类器。"""
+    def _boom(self, *a, **k):
+        raise RuntimeError("HuggingFaceClassifier 需要安装 ML 依赖")
+    import router_system.classifier as C
+    monkeypatch.setattr(C.HuggingFaceClassifier, "__init__", _boom)
+    clf = build_classifier({"type": "hf", "model": "whatever"})
+    assert isinstance(clf, RuleClassifier)
+    assert clf.classify("用 Python 写一个快速排序函数").domain == "code"
+
+
+def test_hf_runtime_failure_falls_back_to_rules():
+    """推理期异常（torch 缺失/tokenizer 损坏）回落内置规则分类器。"""
+    from router_system.classifier import HuggingFaceClassifier
+    hf = HuggingFaceClassifier.__new__(HuggingFaceClassifier)
+    hf.labels = ["code", "math", "legal", "medical", "general"]
+    hf.confidence_floor = 0.55
+    hf._rule_fallback = RuleClassifier(confidence_floor=0.55)
+    r = hf.classify("用 Python 写一个快速排序函数")  # 本环境无 torch/tokenizer -> 必走回落
+    assert r.domain == "code"