Commit the final Qwen MTP primary before saving state

src/engine/metal/qwen_mtplx/session_checkpoint.rs

@@ -10,7 +10,9 @@ use std::fs::{self, File};
 use std::io::{Read, Seek, SeekFrom, Write};
 use std::path::Path;
 
-const MAGIC: &[u8; 8] = b"QWMTKV01";
+// V1 may bank an emitted MTP primary without its trunk/history state (#106).
+// Reject it before decoding tensors; the owner rebuilds the selected cache.
+const MAGIC: &[u8; 8] = b"QWMTKV02";
 const HEADER_BYTES: u64 = 16;
 const MAX_MANIFEST_BYTES: u64 = 64 * 1024 * 1024;
 const IO_CHUNK: usize = 8 * 1024 * 1024;