diff --git a/core/session_manager.py b/core/session_manager.py
index bf7ce74..fae6fe4 100644
--- a/core/session_manager.py
+++ b/core/session_manager.py
@@ -297,7 +297,15 @@ class SessionManager:
                     id=msg_id,
                     session_id=session_id,
                     role=message.role,
-                    content=message.content,
+                    # Multimodal content (image/audio attachments) is a list;
+                    # serialize to JSON so the Text column round-trips via
+                    # _parse_msg_content. Storing the raw list let SQLAlchemy
+                    # bind its single-quoted repr, which _parse_msg_content
+                    # cannot parse (it looks for double-quoted "type"), so the
+                    # attachment was destroyed on reload. Mirrors _persist_message.
+                    content=(json.dumps(message.content)
+                             if isinstance(message.content, list)
+                             else message.content),
                     meta_data=json.dumps(message.metadata) if message.metadata else None,
                     timestamp=now + timedelta(microseconds=i),
                 )
diff --git a/tests/test_replace_messages_multimodal.py b/tests/test_replace_messages_multimodal.py
new file mode 100644
index 0000000..baee597
--- /dev/null
+++ b/tests/test_replace_messages_multimodal.py
@@ -0,0 +1,80 @@
+"""replace_messages must JSON-serialize multimodal (list) content.
+
+A chat with an image/audio attachment carries list content. When such a
+chat is compacted, the manual-compaction path calls replace_messages with
+the retained messages. replace_messages wrote message.content straight into
+the Text column, so SQLAlchemy bound the list\'s single-quoted repr. On
+reload _parse_msg_content only de-serializes a string that contains the
+double-quoted "type", so the repr failed the check and the message came
+back as a corrupted string blob - the attachment was destroyed. The
+sibling _persist_message json.dumps-es list content; replace_messages did
+not.
+"""
+import tempfile
+import uuid
+
+import pytest
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+from sqlalchemy.pool import NullPool
+
+import core.database as cdb
+from core.database import Session as DbSession
+from core.models import ChatMessage
+
+_TMPDB = tempfile.NamedTemporaryFile(suffix=".db", delete=False)
+_ENGINE = create_engine(
+    f"sqlite:///{_TMPDB.name}",
+    connect_args={"check_same_thread": False},
+    poolclass=NullPool,
+)
+cdb.Base.metadata.create_all(_ENGINE)
+_TS = sessionmaker(bind=_ENGINE, autoflush=False, autocommit=False)
+
+
+@pytest.fixture
+def manager(monkeypatch):
+    import core.session_manager as sm
+    monkeypatch.setattr(sm, "SessionLocal", _TS)
+    mgr = sm.SessionManager.__new__(sm.SessionManager)
+    mgr.sessions = {}
+    return mgr
+
+
+def _make_session(sid, owner="alice"):
+    db = _TS()
+    try:
+        db.add(DbSession(id=sid, owner=owner, name="chat", model="gpt-4o",
+                         archived=False, message_count=1))
+        db.commit()
+    finally:
+        db.close()
+
+
+def test_multimodal_content_round_trips_through_replace_messages(manager):
+    sid = "sess-" + uuid.uuid4().hex[:8]
+    _make_session(sid)
+
+    multimodal = [
+        {"type": "text", "text": "what is this?"},
+        {"type": "image_url", "image_url": {"url": "data:image/png;base64,AAAA"}},
+    ]
+    msgs = [ChatMessage(role="user", content=multimodal)]
+    assert manager.replace_messages(sid, msgs) is True
+
+    # Drop the in-memory cache so the next read hydrates from the DB.
+    manager.sessions.clear()
+    reloaded = manager.get_session(sid)
+    assert len(reloaded.history) == 1
+    # Content must come back as the original list, not a repr string blob.
+    assert reloaded.history[0].content == multimodal
+
+
+def test_plain_string_content_still_round_trips(manager):
+    sid = "sess-" + uuid.uuid4().hex[:8]
+    _make_session(sid)
+    msgs = [ChatMessage(role="user", content="just text")]
+    assert manager.replace_messages(sid, msgs) is True
+    manager.sessions.clear()
+    reloaded = manager.get_session(sid)
+    assert reloaded.history[0].content == "just text"