diff --git a/nanobot/session/manager.py b/nanobot/session/manager.py
index efb5b475c..e6d8e21c3 100644
--- a/nanobot/session/manager.py
+++ b/nanobot/session/manager.py
@@ -101,7 +101,11 @@ class Session:
 
     def __post_init__(self) -> None:
         # An out-of-range offset (corrupt metadata) would hide all history; reset it.
-        if not 0 <= self.last_consolidated <= len(self.messages):
+        if (
+            isinstance(self.last_consolidated, bool)
+            or not isinstance(self.last_consolidated, int)
+            or not 0 <= self.last_consolidated <= len(self.messages)
+        ):
             self.last_consolidated = 0
 
     @staticmethod
diff --git a/tests/session/test_consolidated_offset_clamp.py b/tests/session/test_consolidated_offset_clamp.py
index 6f9358ffc..1bad7b1ae 100644
--- a/tests/session/test_consolidated_offset_clamp.py
+++ b/tests/session/test_consolidated_offset_clamp.py
@@ -1,9 +1,12 @@
 """Reset a corrupt last_consolidated offset instead of hiding history (#4066)."""
 
-from nanobot.session.manager import Session
+import json
+from pathlib import Path
+
+from nanobot.session.manager import Session, SessionManager
 
 
-def _session(count: int, last_consolidated: int) -> Session:
+def _session(count: int, last_consolidated: object) -> Session:
     msgs = [{"role": "user", "content": f"msg{i}"} for i in range(count)]
     return Session(key="chan:chat", messages=msgs, last_consolidated=last_consolidated)
 
@@ -13,6 +16,44 @@ def test_out_of_range_offset_is_reset():
     assert _session(3, -5).last_consolidated == 0
 
 
+def test_non_integer_offset_is_reset():
+    for offset in ("999", None, 0.5, True):
+        assert _session(3, offset).last_consolidated == 0
+
+
+def test_loaded_corrupt_offset_keeps_messages(tmp_path: Path):
+    offsets = {
+        "string": "999",
+        "null": None,
+        "float": 0.5,
+        "bool": True,
+    }
+
+    for name, offset in offsets.items():
+        manager = SessionManager(tmp_path / name)
+        path = manager._get_session_path("chan:chat")
+        path.parent.mkdir(parents=True, exist_ok=True)
+        message = {"role": "user", "content": f"survived {name}"}
+        path.write_text(
+            "\n".join([
+                json.dumps({
+                    "_type": "metadata",
+                    "key": "chan:chat",
+                    "metadata": {},
+                    "last_consolidated": offset,
+                }),
+                json.dumps(message),
+            ]) + "\n",
+            encoding="utf-8",
+        )
+
+        session = manager.get_or_create("chan:chat")
+
+        assert session.messages == [message]
+        assert session.last_consolidated == 0
+        assert session.get_history(max_messages=10) == [message]
+
+
 def test_valid_offset_is_preserved():
     session = _session(10, 4)
     assert session.last_consolidated == 4