fix(governance): skip non-finite slo values

apps/api/src/services/governance_agent.py

@@ -399,6 +399,7 @@ class GovernanceAgent:
         2026-04-27 P3.4 by Claude — AI SLO（ADR-100）
         """
         import httpx
+        import math
 
         from src.core.config import settings
 
@@ -457,6 +458,21 @@ class GovernanceAgent:
                             )
                             continue
                         value = float(result_list[0]["value"][1])
+                        if not math.isfinite(value):
+                            results[name] = {
+                                "name": name,
+                                "status": "skipped",
+                                "error": "non_finite_value",
+                                "reason": "prometheus_nan_or_inf",
+                                "hint": "SLO 分母目前沒有足夠事件，等待下一個有效樣本再評估",
+                            }
+                            logger.warning(
+                                "governance_slo_non_finite",
+                                slo=name,
+                                query=query,
+                                value=str(result_list[0]["value"][1]),
+                            )
+                            continue
                         threshold = hard_red_lines[name]
                         target = slo_targets[name]
                         violated = value < threshold