Stage 318: PR #1856 — fix: preserve pending turn during stale cleanup by @ai-ag2026

api/routes.py

@@ -675,6 +675,7 @@ def _clear_stale_stream_state(session) -> bool:
     with _get_session_agent_lock(session.session_id):
         if getattr(session, "active_stream_id", None) != stream_id:
             return False
+        _materialize_pending_user_turn_before_error(session)
         session.active_stream_id = None
         if hasattr(session, "pending_user_message"):
             session.pending_user_message = None
@@ -1508,7 +1509,12 @@ from api.workspace import (
     _workspace_blocked_roots,
 )
 from api.upload import handle_upload, handle_upload_extract, handle_transcribe
-from api.streaming import _sse, _run_agent_streaming, cancel_stream
+from api.streaming import (
+    _sse,
+    _run_agent_streaming,
+    cancel_stream,
+    _materialize_pending_user_turn_before_error,
+)
 from api.providers import get_providers, get_provider_quota, set_provider_key, remove_provider_key
 from api.onboarding import (
     apply_onboarding_setup,

tests/test_issue1361_cancel_data_loss.py

@@ -366,6 +366,40 @@ def test_stream_error_pending_materialization_does_not_duplicate_eager_checkpoin
     assert [m.get("role") for m in s.messages].count("user") == 1
 
 
+def test_stale_stream_cleanup_materializes_pending_turn_before_clearing_state():
+    """A zombie/stale stream repair must preserve the pending user prompt.
+
+    If the process dies after chat_start saved pending_user_message but before the
+    agent merges the user turn, /api/session stale cleanup must not clear that
+    pending field without first appending a durable user message.
+    """
+    from api.routes import _clear_stale_stream_state
+
+    sid = "test_pending_error_d3_stale"
+    s = _make_session(
+        session_id=sid,
+        pending_msg="please make the GUI fully usable",
+        messages=[{"role": "assistant", "content": "previous answer"}],
+    )
+    s.pending_started_at = 1778187755.0
+    s.pending_attachments = [{"name": "visible-state.png"}]
+    # No matching STREAMS entry: this simulates a dead worker/server restart.
+
+    cleared = _clear_stale_stream_state(s)
+
+    assert cleared is True
+    assert s.active_stream_id is None
+    assert s.pending_user_message is None
+    assert s.messages[-1]["role"] == "user"
+    assert s.messages[-1]["content"] == "please make the GUI fully usable"
+    assert s.messages[-1]["timestamp"] == 1778187755
+    assert s.messages[-1]["attachments"] == [{"name": "visible-state.png"}]
+
+    reloaded = models.get_session(sid, metadata_only=False)
+    assert reloaded.messages[-1]["role"] == "user"
+    assert reloaded.messages[-1]["content"] == "please make the GUI fully usable"
+
+
 # ── Structural guard: pin call sites of the materialize helper at error branches ──
 
 def test_materialize_helper_called_immediately_before_error_path_clears():