Identified where in the stream decoder fixture test the error assertion
should be added and what it should validate.
Key findings:
- flate_truncated fixture should emit STREAM_DECODE_ERROR diagnostic
- StreamDecoder::decode() trait doesn't support diagnostics output
- Test loop lacks diagnostic validation
- Assertion should be added after line 326 in test loop
- Test needs to be updated to use decode_stream() which returns DecodeResult with diagnostics
Closes bf-2hjaa.
