fix(decision): derive telegram dedup from incident signals

apps/api/src/services/decision_manager.py

@@ -55,6 +55,20 @@ def _fire_and_forget(coro) -> asyncio.Task:
     return task
 
 
+def _incident_alertname_for_dedup(incident: Incident) -> str:
+    """Return a stable alert name for Telegram fingerprint dedup."""
+    if incident.signals:
+        signal = incident.signals[0]
+        return (
+            signal.labels.get("alertname")
+            or signal.alert_name
+            or signal.annotations.get("summary")
+            or signal.annotations.get("description")
+            or incident.incident_id
+        )
+    return incident.incident_id
+
+
 def _phase2_fallback_reason(package: Any) -> str | None:
     """Return why a Phase 2 package should continue to Playbook/LLM fallback.
 
@@ -212,7 +226,7 @@ async def _push_decision_to_telegram(
         # 改成 alertname+target 構造的 fingerprint key + TTL 86400s，同症狀共用 dedup。
         # Incident 真正 RESOLVED/CLOSED 時走 line 220-226 的 status check 提早 return，不影響復發偵測。
         redis = get_redis()
-        _alertname_fp = (incident.title or "unknown").strip().lower().replace(" ", "_")[:60]
+        _alertname_fp = _incident_alertname_for_dedup(incident).strip().lower().replace(" ", "_")[:60]
         _target_fp = (
             incident.affected_services[0] if incident.affected_services else "unknown"
         ).lower()[:40]
@@ -3236,7 +3250,7 @@ class DecisionManager:
                         # 與 line 217-218 同邏輯，避免 pod restart resend 路徑繞過 fingerprint dedup。
                         # 原本 telegram_sent:{incident_id} TTL 600s 早就過期 → 重啟必重發；
                         # 改 fingerprint + 24h TTL → 同症狀 24h 內任何 INC ID 都不會重推。
-                        _alertname_fp = (getattr(incident, "title", None) or "unknown").strip().lower().replace(" ", "_")[:60]
+                        _alertname_fp = _incident_alertname_for_dedup(incident).strip().lower().replace(" ", "_")[:60]
                         _affected = getattr(incident, "affected_services", None) or []
                         _target_fp = (_affected[0] if _affected else "unknown").lower()[:40]
                         dedup_key = f"telegram_sent:fp:{_alertname_fp}:{_target_fp}"