diff --git a/evolution/__init__.py b/evolution/__init__.py
new file mode 100644
index 0000000..238ff50
--- /dev/null
+++ b/evolution/__init__.py
@@ -0,0 +1 @@
+"""Evolution package for learning-oriented the-door modules."""
diff --git a/tests/test_crisis_synthesizer_integration.py b/tests/test_crisis_synthesizer_integration.py
new file mode 100644
index 0000000..400712a
--- /dev/null
+++ b/tests/test_crisis_synthesizer_integration.py
@@ -0,0 +1,90 @@
+"""Regression tests for crisis_synthesizer integration (issue #121)."""
+
+from __future__ import annotations
+
+import json
+import os
+from unittest.mock import Mock, patch
+
+from crisis_detector import CrisisResult
+from crisis_responder import CrisisResponder
+from crisis.synthesizer_integration import CrisisSynthesizerIntegration
+from evolution.crisis_synthesizer import load_interaction_events
+
+
+def _make_detection(level: str, keywords: list[str]) -> CrisisResult:
+    return CrisisResult(risk_level=level, matched_keywords=keywords, context=[], score=0.9)
+
+
+def test_responder_auto_logs_anonymized_event(tmp_path):
+    integration = CrisisSynthesizerIntegration(enabled=True, log_dir=tmp_path)
+    responder = CrisisResponder(synth_integration=integration, session_id="session-1", async_synth_logging=False)
+
+    detection = _make_detection("HIGH", ["hopeless", "can't go on"])
+    response = responder.respond(detection)
+
+    log_path = tmp_path / "events.jsonl"
+    lines = log_path.read_text(encoding="utf-8").splitlines()
+    assert len(lines) == 1
+    event = json.loads(lines[0])
+    assert event["level"] == "HIGH"
+    assert event["matched_keywords"] == ["hopeless", "can't go on"]
+    assert event["response_type"] == response.risk_level
+    assert isinstance(event["timestamp"], float)
+    assert event["user_continued"] is False
+    assert event["session_hash"]
+    assert "message" not in event
+    assert "session_id" not in event
+    assert log_path.stat().st_mode & 0o777 == 0o600
+
+
+
+def test_next_non_crisis_message_marks_user_continued_append_only(tmp_path):
+    integration = CrisisSynthesizerIntegration(enabled=True, log_dir=tmp_path)
+    responder = CrisisResponder(synth_integration=integration, session_id="session-1", async_synth_logging=False)
+
+    responder.respond(_make_detection("CRITICAL", ["want to die"]))
+    log_path = tmp_path / "events.jsonl"
+    before_size = log_path.stat().st_size
+
+    responder.respond(_make_detection("NONE", []))
+    after_size = log_path.stat().st_size
+
+    assert after_size > before_size
+
+    raw_lines = log_path.read_text(encoding="utf-8").splitlines()
+    assert len(raw_lines) == 2
+    continuation = json.loads(raw_lines[1])
+    assert continuation["event_type"] == "continuation"
+    assert continuation["user_continued"] is True
+
+    folded_events = load_interaction_events(log_path)
+    assert len(folded_events) == 1
+    assert folded_events[0]["continued_conversation"] is True
+    assert folded_events[0]["user_continued"] is True
+
+
+
+def test_env_var_can_disable_logging_entirely(tmp_path):
+    with patch.dict(os.environ, {"CRISIS_SYNTH_ENABLED": "0"}, clear=False):
+        integration = CrisisSynthesizerIntegration(enabled=None, log_dir=tmp_path)
+        responder = CrisisResponder(synth_integration=integration, session_id="session-1", async_synth_logging=False)
+        responder.respond(_make_detection("HIGH", ["hopeless"]))
+
+    assert not (tmp_path / "events.jsonl").exists()
+
+
+@patch("crisis_responder.threading.Thread")
+def test_async_logging_dispatches_to_background_thread(thread_cls):
+    integration = Mock()
+    integration.enabled = True
+    integration.log_crisis_event = Mock()
+    integration.log_user_continued = Mock()
+
+    responder = CrisisResponder(synth_integration=integration, session_id="session-1", async_synth_logging=True)
+    responder.respond(_make_detection("HIGH", ["hopeless"]))
+
+    thread_cls.assert_called_once()
+    _, kwargs = thread_cls.call_args
+    assert kwargs["daemon"] is True
+    thread_cls.return_value.start.assert_called_once()