out of range eror when calling intrinsics on empty contexts

[nrfulton]

Code to reproduce:

import mellea
from mellea.stdlib.components.intrinsic.rag import check_answerability

m = mellea.start_session(backend_name="hf", model_id="ibm-granite/granite-4.0-micro")
check_answerability(
    question="Does our firm have any current investments in the foo industry?",
    documents=["The user works for blah capital", "blah capital leads investment round in acme corp", "acme corp is disrupting the foo industry"],
    context=m.ctx,
    backend=m.backend
)

Expected: answerability intrinsic provides a result.

Actual: out of index error when running isinstance(conversation[0], (list, tuple)) or hasattr(conversation[0], "messages") in transformers.tokenization_utils_base

[akihikokuroda]

The context argument of check_answerability method is expecting ChatContext instead of SimpleContext

mypy result:

     Argument "context" to "check_answerability" has incompatible type "Context"; expected "ChatContext"  [arg-type]                                                                
     Argument "backend" to "check_answerability" has incompatible type "Backend"; expected "AdapterMixin"  [arg-type]                                                              
     Found 2 errors in 1 file (checked 1 source file) 

Adding 'context_type="chat"' in the start_session method argument seems fixing this issue.