Commit the final Qwen MTP primary before saving state

docs/issue106-final-primary/baseline-save.patch

@@ -0,0 +1,22 @@
+--- a/src/engine/metal/qwen_mtplx/issue103_analysis.rs
++++ b/src/engine/metal/qwen_mtplx/issue103_analysis.rs
+@@ -407,6 +407,19 @@
+                     "{}",
+                     serde_json::json!({"case":"mtp_final","exit":if stop_exit {"first_primary_stop"} else {"max_tokens"},"depth":depth,"temperature":temperature,"prompt_ids":ids,"tokens":result.tokens,"key_length":key.len(),"restored_cached_tokens":reused,"trunk_offsets":offsets,"mtp_offset":execution.mtp_offset().unwrap(),"pending":result.pending,"final_state_error":result.final_state_error})
+                 );
++                if depth == 1 && temperature == 0.6 && !stop_exit {
++                    let path = std::env::var_os("DS4_ISSUE106_BAD_CHECKPOINT").unwrap();
++                    let metadata = crate::engine::qwen::QwenMetadata::open(&root, true).unwrap();
++                    let identity = super::session_checkpoint::Identity {
++                        model: metadata.checkpoint_identity(), context: 4096,
++                        vocabulary: metadata.tokenizer.vocab_size() as u32, mtp: true,
++                    };
++                    let mut live = super::request::LiveSession {
++                        current: Some(snapshot), ..Default::default()
++                    };
++                    live.save_checkpoint(std::path::Path::new(&path), identity,
++                        [106; 32], &execution.streams, execution.stream, |_| {}, || false).unwrap();
++                }
+                 assert_eq!(offsets, vec![3; 12]);
+                 assert_eq!(reused, 4);
+                 assert!(result.pending.is_none() && result.final_state_error.is_none());