fix(session_search): exclude current session lineage

Cherry-picked from PR #2201 by @Gutslabs.

session_search resolved hits to parent/root sessions but only excluded
the exact current_session_id. If the active session was a child
continuation (compression/delegation), its parent could still appear
as a 'past' conversation result.

Fix: resolve current_session_id to its lineage root before filtering,
so the entire active lineage (parent and children) is excluded.

tests/tools/test_session_search.py

@@ -214,3 +214,61 @@ class TestSessionSearch:
         # Current session should be skipped, only other_sid should appear
         assert result["sessions_searched"] == 1
         assert current_sid not in [r.get("session_id") for r in result.get("results", [])]
+
+    def test_current_child_session_excludes_parent_lineage(self):
+        """Compression/delegation parents should be excluded for the active child session."""
+        from unittest.mock import MagicMock
+        from tools.session_search_tool import session_search
+
+        mock_db = MagicMock()
+        mock_db.search_messages.return_value = [
+            {"session_id": "parent_sid", "content": "match", "source": "cli",
+             "session_started": 1709500000, "model": "test"},
+        ]
+
+        def _get_session(session_id):
+            if session_id == "child_sid":
+                return {"parent_session_id": "parent_sid"}
+            if session_id == "parent_sid":
+                return {"parent_session_id": None}
+            return None
+
+        mock_db.get_session.side_effect = _get_session
+
+        result = json.loads(session_search(
+            query="test", db=mock_db, current_session_id="child_sid",
+        ))
+
+        assert result["success"] is True
+        assert result["count"] == 0
+        assert result["results"] == []
+        assert result["sessions_searched"] == 0
+
+    def test_current_root_session_excludes_child_lineage(self):
+        """Delegation child hits should be excluded when they resolve to the current root session."""
+        from unittest.mock import MagicMock
+        from tools.session_search_tool import session_search
+
+        mock_db = MagicMock()
+        mock_db.search_messages.return_value = [
+            {"session_id": "child_sid", "content": "match", "source": "cli",
+             "session_started": 1709500000, "model": "test"},
+        ]
+
+        def _get_session(session_id):
+            if session_id == "root_sid":
+                return {"parent_session_id": None}
+            if session_id == "child_sid":
+                return {"parent_session_id": "root_sid"}
+            return None
+
+        mock_db.get_session.side_effect = _get_session
+
+        result = json.loads(session_search(
+            query="test", db=mock_db, current_session_id="root_sid",
+        ))
+
+        assert result["success"] is True
+        assert result["count"] == 0
+        assert result["results"] == []
+        assert result["sessions_searched"] == 0