Preserve source tool JSON alongside decoded API values so Flint can retain
numeric types and schema order in prompts. Existing API marshaling is unchanged.
Assemble ModelOpt expert banks during safetensors import, and reject direct
Flint NVFP4 creation before conversion. Other models retain their existing
import and quantization paths.
Add optional learned sinks and device causal masks to shared MLX attention.
Existing callers retain the no-sink and host-mask paths; Flint opts into the
new behavior.