fix(api): stabilize flywheel success rate window

apps/api/src/services/flywheel_stats_service.py

@@ -241,6 +241,9 @@ class FlywheelStatsService:
             # 執行成功率的 source of truth 是 auto_repair_executions。
             # Redis playbook success_count/failure_count 會因回寫鏈路中斷而落後，
             # 造成 governance / heartbeat 判定「飛輪沒有執行」。
+            # 2026-05-29 Codex:
+            # 24h 低流量不是資料管線斷流；若 24h 未達最小樣本，改用 7d
+            # 穩定窗口，避免 FlywheelExecutionRateMissing 長期誤報。
             try:
                 async with get_db_context() as db:
                     row = await db.execute(
@@ -257,7 +260,22 @@ class FlywheelStatsService:
                     if db_total_exec >= FLYWHEEL_MIN_SAMPLE:
                         db_total_success = int(repair_stats.success or 0)
                         return count, db_total_success / db_total_exec
-                    if db_total_exec > 0:
+
+                    fallback_row = await db.execute(
+                        text("""
+                            SELECT
+                                COUNT(*) FILTER (WHERE success IS TRUE) AS success,
+                                COUNT(*) AS total
+                            FROM auto_repair_executions
+                            WHERE created_at >= NOW() - interval '7 days'
+                        """)
+                    )
+                    fallback_stats = fallback_row.one()
+                    fallback_total = int(fallback_stats.total or 0)
+                    if fallback_total >= FLYWHEEL_MIN_SAMPLE:
+                        fallback_success = int(fallback_stats.success or 0)
+                        return count, fallback_success / fallback_total
+                    if db_total_exec > 0 or fallback_total > 0:
                         return count, None
             except Exception:
                 logger.warning("flywheel_stats_auto_repair_execution_query_failed")