Commit the final Qwen MTP primary before saving state

src/engine/metal/qwen_mtplx/issue106_product.rs

@@ -0,0 +1,101 @@
+//! Existing Generator rejection/rebuild path for a real pre-fix checkpoint.
+use super::*;
+use crate::engine::{Generator, metal::Executor};
+use crate::settings::{
+    GenerationPreferences, RuntimePreferences, SpeculativePreferences, effective_settings,
+};
+use std::sync::Arc;
+
+#[test]
+#[ignore = "installed model and actual pre-fix checkpoint; external memory guard required"]
+fn issue106_product_discards_old_checkpoint_and_recovers_cold() {
+    let root = std::path::PathBuf::from(std::env::var_os("DS4_QWEN38_ARTIFACTS").unwrap());
+    let old = std::path::PathBuf::from(std::env::var_os("DS4_ISSUE106_BAD_CHECKPOINT").unwrap());
+    let directory =
+        std::path::PathBuf::from(std::env::var_os("DS4_ISSUE106_DIR").unwrap()).join("product");
+    std::fs::create_dir_all(&directory).unwrap();
+    let effective = effective_settings(
+        crate::model::ModelChoice::Qwen38FlashNext,
+        &GenerationPreferences {
+            context_tokens: 4096,
+            max_generated_tokens: 1,
+            temperature: Some(0.6),
+            ..Default::default()
+        },
+        &RuntimePreferences {
+            speculative: SpeculativePreferences {
+                glm_mtp: true,
+                ..Default::default()
+            },
+            ..Default::default()
+        },
+        root.parent().unwrap(),
+    )
+    .unwrap();
+    let mut settings = effective.turn;
+    settings.seed = Some(0);
+    settings.kv_cache.min_tokens = 0;
+    let mut generator = Generator::open(
+        &effective.engine,
+        Arc::new(Metrics::new(&directory.join("metrics"))),
+    )
+    .unwrap();
+    let path = directory.join("old.bin");
+    std::fs::copy(&old, &path).unwrap();
+    let selection = generator.select_checkpoint(&path, |_| true).unwrap();
+    assert!(!selection.found && selection.incompatible);
+    assert!(!path.exists());
+    let Executor::QwenMtplx(owner) = &mut generator.executor else {
+        unreachable!()
+    };
+    assert!(owner.live.current.is_none() && owner.live.prefix.is_none());
+    let messages = [ChatTurn {
+        user: true,
+        tool: false,
+        system: false,
+        skip_previous_eos: false,
+        reasoning: None,
+        reasoning_complete: true,
+        content: "Say hello.".into(),
+    }];
+    let mut states = Vec::new();
+    for target in [&path, &directory.join("fresh.bin")] {
+        let out = generator
+            .generate(
+                target,
+                None,
+                &messages,
+                &settings,
+                &AtomicBool::new(false),
+                |_, _| {},
+                |_, _, _| {},
+                |_| {},
+            )
+            .unwrap();
+        assert_eq!(out.cached_tokens, 0);
+        assert_eq!(&std::fs::read(target).unwrap()[..8], b"QWMTKV02");
+        let Executor::QwenMtplx(owner) = &mut generator.executor else {
+            unreachable!()
+        };
+        let saved = owner.live.current.as_ref().unwrap();
+        let mut hashes = Vec::new();
+        let payload = saved
+            .encode_payload(
+                256,
+                &owner.execution.streams,
+                owner.execution.stream,
+                |_, bytes| {
+                    hashes.push(crate::engine::metal::qwen_mtplx_tests::hex_digest(&bytes));
+                    Ok(())
+                },
+                || false,
+            )
+            .unwrap();
+        states.push(serde_json::json!({"tokens":saved.token_ids,"payload":payload,"hashes":hashes,"text":out.message.content,"reasoning":out.message.reasoning}));
+    }
+    assert_eq!(states[0], states[1]);
+    println!(
+        "{}",
+        serde_json::json!({"case":"product_checkpoint_recovery","old_removed":true,"cold_tokens":0,"new_magic":"QWMTKV02","fresh_state_equal":true})
+    );
+}