Keep the diagnostic helper's object input contract while narrowing locally
for static checking, avoiding a runtime Iterable guard that would reject
legacy sequence-protocol objects.

Test Plan:

```
pyrefly check --baseline agent_space/compiler-exception-pyrefly-baseline.json torch/_dynamo/exc.py torch/_inductor/exc.py torch/_dynamo/utils.py torch/_functorch/_aot_autograd/runtime_wrappers.py
```

```
UV_NO_CONFIG=1 lintrunner -a --skip PYREFLY torch/_dynamo/exc.py torch/_inductor/exc.py torch/_dynamo/utils.py torch/_functorch/_aot_autograd/runtime_wrappers.py
```

Authored with assistance from an AI coding assistant.