fix: address M2 verifier findings in soak harness

tests/unit/test_soak_corpus.py

@@ -195,3 +195,50 @@ class TestInvariants:
             _row("c", session="r-p1"),  # 非 P3 剔除
         ]
         assert structured_success_rate(rows, session_suffix="-p3") == pytest.approx(0.5)
+
+
+class TestLiveInvariantsAndCaps:
+    def test_capped_budget_clamps_to_signed_values(self):
+        from tools.soak.scoreboard import capped_budget
+
+        assert capped_budget("P1", 9999) == 500
+        assert capped_budget("P6", 100) == 100
+
+    async def test_gate_reenterable_detects_hung_probe(self):
+        from tools.soak.scoreboard import inv_gate_reenterable
+
+        class _Decision:
+            def __init__(self, allowed, state, is_probe=False):
+                self.allowed = allowed
+                self.state = state
+                self.is_probe = is_probe
+                self.retry_after_s = 30.0
+
+        class _Gate:
+            def __init__(self, decision):
+                self._d = decision
+                self.released = 0
+
+            async def try_enter(self, name, owner):
+                return self._d
+
+            async def release_probe(self, entry):
+                self.released += 1
+
+        healthy = _Gate(_Decision(True, "closed"))
+        await inv_gate_reenterable(healthy, ["s1"])
+        probe_gate = _Gate(_Decision(True, "half_open", is_probe=True))
+        await inv_gate_reenterable(probe_gate, ["s1"])
+        assert probe_gate.released == 1  # 探针当场归还,不留新悬挂
+        await inv_gate_reenterable(_Gate(_Decision(False, "open")), ["s1"])  # 冷却合法
+        with pytest.raises(AssertionError, match="悬挂"):
+            await inv_gate_reenterable(_Gate(_Decision(False, "half_open")), ["s1"])
+
+    def test_fault_errors_presence(self):
+        from tools.soak.scoreboard import inv_fault_errors_present
+
+        rows = [_row("a", source="bad_1", error="SourceDeadError: 401"), _row("b")]
+        inv_fault_errors_present(rows, fault_source_names=["bad_1"])
+        inv_fault_errors_present(rows, fault_source_names=[])  # 未配故障源直接通过
+        with pytest.raises(AssertionError):
+            inv_fault_errors_present([_row("c")], fault_source_names=["bad_1"])