fix: show RDG flap badge on 302 and 303 events in SAC UI (0.20.5)

Seaca surfaced flap via Problems; the web UI only flagged 303 in DB and had
no visible label. Resolve flap pairs at read time and show badge plus qwinsta
on both sides of 302→303.

backend/app/services/rdg_session_flap.py

@@ -122,3 +122,75 @@ def evaluate_rdg_session_flap(db: Session, event: Event) -> RuleMatch | None:
 def event_has_rdg_flap(event: Event) -> bool:
     details = event.details if isinstance(event.details, dict) else {}
     return details.get("rdg_flap") is True
+
+
+def _stored_flap_pair_id(event: Event) -> int | None:
+    details = event.details if isinstance(event.details, dict) else {}
+    raw = details.get("rdg_flap_pair_event_id")
+    if raw is None:
+        return None
+    try:
+        return int(raw)
+    except (TypeError, ValueError):
+        return None
+
+
+def find_rdg_end_after_success(db: Session, success_event: Event) -> Event | None:
+    """303 с rdg_flap, у которого пара — этот 302 (или вычисляется по окну)."""
+    if success_event.type != RDG_SUCCESS_TYPE:
+        return None
+    settings = get_settings()
+    min_sec = settings.sac_rdg_flap_window_min_sec
+    max_sec = settings.sac_rdg_flap_window_max_sec
+    start_at = _as_utc(success_event.occurred_at)
+    window_start = start_at + timedelta(seconds=min_sec)
+    window_end = start_at + timedelta(seconds=max_sec)
+
+    candidates = db.scalars(
+        select(Event)
+        .where(
+            Event.host_id == success_event.host_id,
+            Event.type.in_(RDG_END_TYPES),
+            Event.occurred_at >= window_start,
+            Event.occurred_at <= window_end,
+            Event.id != success_event.id,
+        )
+        .order_by(Event.occurred_at.asc())
+    ).all()
+
+    for end in candidates:
+        if not _users_match(end, success_event):
+            continue
+        if not _internal_ips_compatible(end, success_event):
+            continue
+        pair_id = _stored_flap_pair_id(end)
+        if pair_id == success_event.id:
+            return end
+        prior = find_rdg_success_before_end(db, end)
+        if prior is not None and prior.id == success_event.id:
+            return end
+    return None
+
+
+def resolve_rdg_flap_summary(
+    db: Session, event: Event
+) -> tuple[bool, int | None, int | None]:
+    """
+    (rdg_flap, pair_event_id, qwinsta_event_id).
+    qwinsta_event_id — всегда 303; для 302 указывает на связанный end-event.
+    """
+    if event_has_rdg_flap(event):
+        pair_id = _stored_flap_pair_id(event)
+        return True, pair_id, event.id
+
+    if event.type in RDG_END_TYPES:
+        prior = find_rdg_success_before_end(db, event)
+        if prior is not None:
+            return True, prior.id, event.id
+
+    if event.type == RDG_SUCCESS_TYPE:
+        end = find_rdg_end_after_success(db, event)
+        if end is not None:
+            return True, end.id, end.id
+
+    return False, None, None