RoundRobinModel: _set_span_attributes calls nonexistent Model.model_attributes (always fails, silently suppressed); factory can insert None sub-models causing intermittent AttributeError every Nth request

Problem

RoundRobinModel (code_puppy/round_robin_model.py) has three issues:

1. _set_span_attributes calls a method that doesn't exist on pydantic-ai Model

Line ~148:

span.set_attributes(model.model_attributes(model))

pydantic_ai.models.Model has no model_attributes method (verified against the installed version: 'model_attributes' in dir(Model) is False). This would raise AttributeError on every call — it's only invisible because the whole body is wrapped in with suppress(Exception). So the observability feature this method exists for silently never works: errors passing silently, and dead code in disguise.

2. model_factory can insert None into the rotation

model_factory.py round_robin branch (lines ~960-972):

for name in model_names:
    model = ModelFactory.get_model(name, config)
    models.append(model)

ModelFactory.get_model() returns None for many failure modes (missing API key, plugin failure). A None lands in the rotation and only blows up later with an opaque AttributeError: 'NoneType' object has no attribute 'prepare_request' mid-conversation — on a schedule (every Nth request), which makes for a maddening intermittent bug. Validate at construction: skip-and-warn or raise immediately if any sub-model is None.

3. system / base_url properties read _current_index without the lock

Minor race: rotation mutates _current_index under _lock, but the properties read it unlocked. Worst case is reporting the wrong sub-model's metadata; worth a comment or a lock for consistency.

Also: the bare try/except Exception: raise around current_model.request(...) (lines ~108-117) is a no-op wrapper — delete it.

Suggested fix

• Fix or delete _set_span_attributes; if keeping it, use real pydantic-ai attributes (e.g. {\"gen_ai.request.model\": model.model_name}) and stop suppressing all exceptions.
• In model_factory, raise ValueError(f\"Round-robin sub-model {name!r} failed to initialize\") when get_model returns None.

Filed by Zen Reviewer A (code-puppy-60635a)

Start in code_puppy/round_robin_model.py, especially _set_span_attributes, request(), and the system/base_url properties, then inspect the round_robin branch in model_factory.py. Trace how ModelFactory.get_model() failures enter the rotation and review the lock usage around _current_index. Done means failed sub-models are handled at construction, span metadata uses supported model attributes or is removed, and the no-op exception wrapper is gone.