diff --git a/api/streaming.py b/api/streaming.py
index 09022ff2..ff1e4a07 100644
--- a/api/streaming.py
+++ b/api/streaming.py
@@ -3946,6 +3946,14 @@ def _run_agent_streaming(
                                 _ckpt_thread.join(timeout=15)
                             _lock_ctx = _agent_lock if _agent_lock is not None else contextlib.nullcontext()
                             with _lock_ctx:
+                                if not ephemeral and not _stream_writeback_is_current(s, stream_id):
+                                    logger.info(
+                                        "Skipping stale stream self-heal writeback for session %s stream %s; active_stream_id=%s",
+                                        getattr(s, 'session_id', session_id),
+                                        stream_id,
+                                        getattr(s, 'active_stream_id', None),
+                                    )
+                                    return
                                 _result_messages = _heal_result.get('messages') or _previous_context_messages
                                 _next_context_messages = _restore_reasoning_metadata(
                                     _previous_context_messages, _result_messages,
@@ -3987,6 +3995,14 @@ def _run_agent_streaming(
             # API calls so the LLM never sees its own error as prior context on the next turn.
             _lock_ctx = _agent_lock if _agent_lock is not None else contextlib.nullcontext()
             with _lock_ctx:
+                if not ephemeral and not _stream_writeback_is_current(s, stream_id):
+                    logger.info(
+                        "Skipping stale stream error writeback for session %s stream %s; active_stream_id=%s",
+                        getattr(s, 'session_id', session_id),
+                        stream_id,
+                        getattr(s, 'active_stream_id', None),
+                    )
+                    return
                 _materialize_pending_user_turn_before_error(s)
                 s.active_stream_id = None
                 s.pending_user_message = None
diff --git a/tests/test_stale_stream_writeback.py b/tests/test_stale_stream_writeback.py
index 03aa55da..1a4d2398 100644
--- a/tests/test_stale_stream_writeback.py
+++ b/tests/test_stale_stream_writeback.py
@@ -87,3 +87,29 @@ def test_success_path_checks_stream_ownership_before_persisting_result():
     assert compression_pos != -1
     assert guard_pos < result_merge_pos
     assert guard_pos < compression_pos
+
+
+def test_self_heal_retry_success_checks_stream_ownership_before_writeback():
+    src = Path("api/streaming.py").read_text(encoding="utf-8")
+    start = src.index("logger.info('[webui] self-heal (except path): retrying stream")
+    end = src.index("logger.info('[webui] self-heal (except path): retry succeeded')", start)
+    block = src[start:end]
+    guard = "if not ephemeral and not _stream_writeback_is_current(s, stream_id):"
+
+    assert guard in block
+    assert block.index(guard) < block.index("_result_messages = _heal_result.get('messages') or _previous_context_messages")
+    assert block.index(guard) < block.index("s.save()")
+
+
+def test_outer_exception_path_checks_stream_ownership_before_error_writeback():
+    src = Path("api/streaming.py").read_text(encoding="utf-8")
+    outer_error_payload = src.index("_error_payload = _provider_error_payload(err_str, _exc_type, _exc_hint)")
+    start = src.index("# Persist the error so it survives page reload.", outer_error_payload)
+    end = src.index("put('apperror', _error_payload)", start)
+    block = src[start:end]
+    guard = "if not ephemeral and not _stream_writeback_is_current(s, stream_id):"
+
+    assert guard in block
+    assert block.index(guard) < block.index("_materialize_pending_user_turn_before_error(s)")
+    assert block.index(guard) < block.index("s.active_stream_id = None")
+    assert block.index(guard) < block.index("s.messages.append(_error_message)")