BUG: NaN values in GGUF→APR→GGUF roundtrip (Jidoka PMAT-187)

[noahgift]

Summary

The test_roundtrip_gguf_apr_gguf test is failing with NaN detection in tensor data during GGUF round-trip conversion.

Error

PMAT-187: Tensor 'blk.0.attn_k.weight' contains 322 NaN values (data corruption detected). 
Toyota Way: Stop the line - do not pass defects downstream.

Test

// tests/rosetta_dangerous.rs:470
#[test]
fn test_roundtrip_gguf_apr_gguf() {
    // Uses: qwen2.5-coder-1.5b-instruct-q4_k_m.gguf
}

Related

• Jidoka validation added in f2f6a96 (PMAT-187)
• Recent format changes: PMAT-197, REGRESSION: Format conversion still produces large diffs after #177 fix #181, P0 CRITICAL: Format conversion introduces NaN/Inf corruption in tensor weights #177

Investigation Needed

1. Check Q4_K dequantization for NaN generation
2. Check scale/zero-point handling in quantized formats
3. Verify APR→GGUF conversion preserves quantization metadata