fix(scheduler): address !7 REQUEST_CHANGES

- seed: check completed_key before no_source so same-day last_completed
  is already_completed (not 10m retry)
- scheduler: resolve TaskControl ok/error before logging; ok=False logs
  task_fail, not task_ok
- candidate_cleanup: catch failures, record task, retry ~5m like discover

reaction_board/services/snapshot.py

@@ -538,16 +538,8 @@ class SnapshotService:
             raise ValueError(f"日期格式必须是 YYYY-MM-DD: {stat_date!r}")
 
         summary = SnapshotSummary(stat_date=stat_date, started_at=now)
-        source = self.repo.kv_get("snapshot:last_completed")
-        if not source or source >= stat_date:
-            self._log(
-                "info", "snapshot.seed_skip",
-                stat_date=stat_date, reason="no_source", source=source,
-            )
-            summary.finished_at = self._now()
-            summary.completed = False
-            summary.reason = "no_source"
-            return summary
+        # 目标日已完成：先于 no_source。全站快照当天完成后
+        # last_completed == stat_date，不可误判为无源再 10 分钟重试。
         if self.repo.kv_get(self.completed_key(stat_date)) == "1":
             self._log(
                 "info", "snapshot.seed_skip",
@@ -558,6 +550,16 @@ class SnapshotService:
             summary.already_completed = True
             summary.reason = "already_completed"
             return summary
+        source = self.repo.kv_get("snapshot:last_completed")
+        if not source or source >= stat_date:
+            self._log(
+                "info", "snapshot.seed_skip",
+                stat_date=stat_date, reason="no_source", source=source,
+            )
+            summary.finished_at = self._now()
+            summary.completed = False
+            summary.reason = "no_source"
+            return summary
         if self.repo.kv_get(self.seeded_key(stat_date)) == "1":
             self._log(
                 "info", "snapshot.seed_skip",