fix(session): reset out-of-range last_consolidated to recover hidden history (#4066)

tests/session/test_consolidated_offset_clamp.py

@@ -0,0 +1,19 @@
+"""Reset a corrupt last_consolidated offset instead of hiding history (#4066)."""
+
+from nanobot.session.manager import Session
+
+
+def _session(count: int, last_consolidated: int) -> Session:
+    msgs = [{"role": "user", "content": f"msg{i}"} for i in range(count)]
+    return Session(key="chan:chat", messages=msgs, last_consolidated=last_consolidated)
+
+
+def test_out_of_range_offset_is_reset():
+    assert _session(10, 999).last_consolidated == 0
+    assert _session(3, -5).last_consolidated == 0
+
+
+def test_valid_offset_is_preserved():
+    session = _session(10, 4)
+    assert session.last_consolidated == 4
+    assert len(session.get_history()) == 6