fix(compression): make clarify summaries UTF-8 safe

agent/context_compressor.py

@@ -1342,7 +1342,14 @@ def _summarize_tool_result_unguarded(tool_name: str, tool_args: str, tool_conten
             and all(isinstance(item, str) and item for item in response)
         )
         if resolved:
-            summary = response_prefix + json.dumps(response, ensure_ascii=False)
+            # Keep ordinary Unicode intact while escaping lone UTF-16
+            # surrogates so the compacted message remains UTF-8/SQLite safe.
+            serialized_response = (
+                json.dumps(response, ensure_ascii=False)
+                .encode("utf-8", errors="backslashreplace")
+                .decode("utf-8")
+            )
+            summary = response_prefix + serialized_response
             if len(summary) > max_summary_chars:
                 summary = (
                     summary[: max_summary_chars - len(truncation_marker)].rstrip()

tests/agent/test_context_compressor.py

@@ -99,6 +99,15 @@ class TestSummarizeToolResultClarify:
         assert first_summary.endswith("...[truncated]")
         assert second_summary == first_summary
 
+    def test_unpaired_surrogates_are_safe_for_utf8_persistence(self):
+        content = json.dumps({"user_response": "\ud83d" * 1_000})
+
+        summary = _summarize_tool_result("clarify", "{}", content)
+
+        assert len(summary) <= 200
+        assert summary.encode("utf-8")
+        assert "\\ud83d" in summary
+
     @pytest.mark.parametrize(
         "content",
         [