test(session): reproduce orphaned tool results from save-boundary overshoot (#4006)

tests/session/test_turn_continuation.py

@@ -14,6 +14,7 @@ from nanobot.session.turn_continuation import (
     INTERNAL_CONTINUATION_META,
     INTERNAL_CONTINUATION_PENDING_META,
     INTERNAL_CONTINUATION_RUN_STARTED_AT_META,
+    _save_skip_for_turn,
     internal_continuation_pending,
     internal_continuation_run_started_at,
     maybe_continue_turn,
@@ -138,3 +139,35 @@ def test_internal_continuation_requires_budget_boundary_and_queue():
         pending_queue_available=True,
         session_metadata={},
     )
+
+
+def test_save_skip_matches_prefix_when_current_message_merged():
+    # ``build_messages`` merges the current user message into a same-role
+    # history tail, so the prompt prefix is ``1 + history_count`` instead of
+    # ``2 + history_count``. The old boundary then cut the first new-turn
+    # assistant message (carrying tool_calls) from persistence, leaving its
+    # tool results orphaned in session history (#4006).
+    skip = _save_skip_for_turn(
+        message_metadata=None,
+        initial_message_count=2,  # [system, merged user]
+        history_count=1,
+        user_persisted_early=True,
+    )
+    assert skip == 2
+
+
+def test_save_skip_unchanged_for_standalone_current_message():
+    # [system, history user, current user] — early-persisted current message.
+    assert _save_skip_for_turn(
+        message_metadata=None,
+        initial_message_count=3,
+        history_count=1,
+        user_persisted_early=True,
+    ) == 3
+    # Same prefix, current message not persisted early: re-save it.
+    assert _save_skip_for_turn(
+        message_metadata=None,
+        initial_message_count=3,
+        history_count=1,
+        user_persisted_early=False,
+    ) == 2