diff --git a/gateway/run.py b/gateway/run.py
index b8df4deca..8154b76f1 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -984,8 +984,7 @@ class GatewayRunner:
         source = event.source
         
         # Get existing session key
-        session_key = f"agent:main:{source.platform.value}:" + \
-                      (f"dm" if source.chat_type == "dm" else f"{source.chat_type}:{source.chat_id}")
+        session_key = self.session_store._generate_session_key(source)
         
         # Memory flush before reset: load the old transcript and let a
         # temporary agent save memories before the session is wiped.
diff --git a/tests/gateway/test_session.py b/tests/gateway/test_session.py
index 2f5f4e4a5..979ee6d44 100644
--- a/tests/gateway/test_session.py
+++ b/tests/gateway/test_session.py
@@ -1,9 +1,13 @@
 """Tests for gateway session management."""
 
+import json
 import pytest
+from pathlib import Path
+from unittest.mock import patch, MagicMock
 from gateway.config import Platform, HomeChannel, GatewayConfig, PlatformConfig
 from gateway.session import (
     SessionSource,
+    SessionStore,
     build_session_context,
     build_session_context_prompt,
 )
@@ -199,3 +203,59 @@ class TestBuildSessionContextPrompt:
         prompt = build_session_context_prompt(ctx)
 
         assert "WhatsApp" in prompt or "whatsapp" in prompt.lower()
+
+
+class TestSessionStoreRewriteTranscript:
+    """Regression: /retry and /undo must persist truncated history to disk."""
+
+    @pytest.fixture()
+    def store(self, tmp_path):
+        config = GatewayConfig()
+        with patch("gateway.session.SessionStore._ensure_loaded"):
+            s = SessionStore(sessions_dir=tmp_path, config=config)
+        s._db = None  # no SQLite for these tests
+        s._loaded = True
+        return s
+
+    def test_rewrite_replaces_jsonl(self, store, tmp_path):
+        session_id = "test_session_1"
+        # Write initial transcript
+        for msg in [
+            {"role": "user", "content": "hello"},
+            {"role": "assistant", "content": "hi"},
+            {"role": "user", "content": "undo this"},
+            {"role": "assistant", "content": "ok"},
+        ]:
+            store.append_to_transcript(session_id, msg)
+
+        # Rewrite with truncated history
+        store.rewrite_transcript(session_id, [
+            {"role": "user", "content": "hello"},
+            {"role": "assistant", "content": "hi"},
+        ])
+
+        reloaded = store.load_transcript(session_id)
+        assert len(reloaded) == 2
+        assert reloaded[0]["content"] == "hello"
+        assert reloaded[1]["content"] == "hi"
+
+    def test_rewrite_with_empty_list(self, store):
+        session_id = "test_session_2"
+        store.append_to_transcript(session_id, {"role": "user", "content": "hi"})
+
+        store.rewrite_transcript(session_id, [])
+
+        reloaded = store.load_transcript(session_id)
+        assert reloaded == []
+
+
+class TestSessionStoreEntriesAttribute:
+    """Regression: /reset must access _entries, not _sessions."""
+
+    def test_entries_attribute_exists(self):
+        config = GatewayConfig()
+        with patch("gateway.session.SessionStore._ensure_loaded"):
+            store = SessionStore(sessions_dir=Path("/tmp"), config=config)
+        store._loaded = True
+        assert hasattr(store, "_entries")
+        assert not hasattr(store, "_sessions")