bug: validation_ctx parameter in SamplingStrategy.sample() exists but is not being used in the validation call

[akihikokuroda]

The validation_ctx parameter in SamplingStrategy.sample() exists but is currently not being used in the validation call!

In mellea/stdlib/sampling/base.py line 128:
validation_ctx = validation_ctx if validation_ctx is not None else context

But at line 200-208, validation uses result_ctx instead:
val_scores_co = mfuncs.avalidate(
reqs=reqs,
context=result_ctx, # ← Uses result_ctx, NOT validation_ctx!
backend=backend,
output=result,
...
)

Solution Path
To enable HallucinationRequirement to work seamlessly with instruct():

Option 1: Fix the Sampling Strategy (Recommended)
Change line 202 in mellea/stdlib/sampling/base.py from:
context=result_ctx,
to:
context=validation_ctx,

This would allow passing a custom validation context with documents attached.

Option 2: Enhance instruct() to Support RAG Validation
Modify instruct() to:

Accept a validation_documents parameter
Automatically attach documents to the generated message
Pass the modified context as validation_ctx to the sampling strat

[jakelorocco]

I think changes to sampling strategies and validation require a larger conversation. See: #426.