diff --git a/services/aggregation/worker.py b/services/aggregation/worker.py
index 80cd736..7ef1388 100644
--- a/services/aggregation/worker.py
+++ b/services/aggregation/worker.py
@@ -11,6 +11,7 @@ from __future__ import annotations
 import json
 import logging
 import time
+import uuid as _uuid
 from dataclasses import dataclass
 from datetime import datetime, timedelta, timezone
 from typing import Any
@@ -760,6 +761,15 @@ INSERT INTO trend_evidence (
 """
 
 
+def _is_valid_uuid(val: str) -> bool:
+    """Check if a string is a valid UUID (pattern signal IDs are not)."""
+    try:
+        _uuid.UUID(val)
+        return True
+    except (ValueError, AttributeError):
+        return False
+
+
 async def persist_trend_evidence(
     pool: asyncpg.Pool,
     trend_window_id: str,
@@ -769,12 +779,17 @@ async def persist_trend_evidence(
     """Insert evidence mapping rows for a trend window. Returns count inserted."""
     rows: list[tuple[str, str, str, float, float, float, float, float, float]] = []
     for ev in supporting:
+        # Skip non-UUID document IDs (e.g. pattern signal synthetic IDs)
+        if not _is_valid_uuid(ev.document_id):
+            continue
         rows.append((
             trend_window_id, ev.document_id, "supporting",
             ev.rank_score, ev.weight_component, ev.impact_component,
             ev.recency_component, ev.confidence_component, ev.sentiment_value,
         ))
     for ev in opposing:
+        if not _is_valid_uuid(ev.document_id):
+            continue
         rows.append((
             trend_window_id, ev.document_id, "opposing",
             ev.rank_score, ev.weight_component, ev.impact_component,