scratch_size_bytes=20480 (alloc dwords=5120)
  access scratch[1073741824] (alloc dwords=5120)
RESULT: BUGGY - guard bypassed (0xFFFFFFFC + 4 = 0 wraps to 0 <= 20480)
---PATCHED---
scratch_size_bytes=20480 (alloc dwords=5120)
RESULT: PATCHED - u64 guard rejects fb_base=0xfffffffc idx=1