fix: session_search fallback preview on summarization failure (salvage #3413)

tools/session_search_tool.py

@@ -392,23 +392,30 @@ async def _summarize_all() -> List[Union[str, Exception]]:
             }, ensure_ascii=False)
 
         summaries = []
-        for (session_id, match_info, _, _), result in zip(tasks, results):
+        for (session_id, match_info, conversation_text, _), result in zip(tasks, results):
             if isinstance(result, Exception):
                 logging.warning(
                     "Failed to summarize session %s: %s",
-                    session_id,
-                    result,
-                    exc_info=True,
+                    session_id, result, exc_info=True,
                 )
-                continue
+                result = None
+
+            entry = {
+                "session_id": session_id,
+                "when": _format_timestamp(match_info.get("session_started")),
+                "source": match_info.get("source", "unknown"),
+                "model": match_info.get("model"),
+            }
+
             if result:
-                summaries.append({
-                    "session_id": session_id,
-                    "when": _format_timestamp(match_info.get("session_started")),
-                    "source": match_info.get("source", "unknown"),
-                    "model": match_info.get("model"),
-                    "summary": result,
-                })
+                entry["summary"] = result
+            else:
+                # Fallback: raw preview so matched sessions aren't silently
+                # dropped when the summarizer is unavailable (fixes #3409).
+                preview = (conversation_text[:500] + "\n…[truncated]") if conversation_text else "No preview available."
+                entry["summary"] = f"[Raw preview — summarization unavailable]\n{preview}"
+
+            summaries.append(entry)
 
         return json.dumps({
             "success": True,