diff --git a/.github/workflows/test-checkpoint-selection.yml b/.github/workflows/test-checkpoint-selection.yml
new file mode 100644
index 0000000000..1906cbf310
--- /dev/null
+++ b/.github/workflows/test-checkpoint-selection.yml
@@ -0,0 +1,65 @@
+name: Validate checkpoint selection
+
+on:
+  pull_request:
+    paths:
+      - "funasr/train_utils/**"
+      - "tests/test_checkpoint_metric_*.py"
+      - "tests/test_trainer_ds_unvalidated_ckpt.py"
+      - "tests/test_train_ds_distributed_config.py"
+      - "tests/test_sensevoice_continual_finetuning_docs.py"
+      - "examples/industrial_data_pretraining/sense_voice/**"
+      - ".github/workflows/test-checkpoint-selection.yml"
+  push:
+    branches: [main]
+    paths:
+      - "funasr/train_utils/**"
+      - "tests/test_checkpoint_metric_*.py"
+      - "tests/test_trainer_ds_unvalidated_ckpt.py"
+      - "tests/test_train_ds_distributed_config.py"
+      - "tests/test_sensevoice_continual_finetuning_docs.py"
+      - "examples/industrial_data_pretraining/sense_voice/**"
+      - ".github/workflows/test-checkpoint-selection.yml"
+
+permissions:
+  contents: read
+
+jobs:
+  checkpoint-selection:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    env:
+      OMP_NUM_THREADS: "1"
+      MKL_NUM_THREADS: "1"
+      PYTEST_DISABLE_PLUGIN_AUTOLOAD: "1"
+      TORCH_FORCE_WEIGHTS_ONLY_LOAD: "1"
+      HF_HUB_OFFLINE: "1"
+      GLOO_SOCKET_IFNAME: lo
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+          cache: pip
+      - name: Install CPU test dependencies
+        run: |
+          python -m pip install torch==2.10.0 torchaudio==2.10.0 --index-url https://download.pytorch.org/whl/cpu
+          python -m pip install "numpy<2" kaldiio librosa rapidfuzz six pytest omegaconf hydra-core pyyaml tqdm
+      - name: Check recipe syntax
+        run: bash -n examples/industrial_data_pretraining/sense_voice/finetune.sh
+      - name: Test validation, checkpoint lifecycle and two-rank collectives
+        run: |
+          python -m pytest -q \
+            tests/test_checkpoint_metric_presence.py \
+            tests/test_checkpoint_metric_distributed.py \
+            tests/test_trainer_ds_unvalidated_ckpt.py \
+            tests/test_train_ds_distributed_config.py \
+            tests/test_sensevoice_continual_finetuning_docs.py \
+            --junitxml=checkpoint-selection.xml
+      - name: Save test report
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: checkpoint-selection-report
+          path: checkpoint-selection.xml
+          if-no-files-found: error
diff --git a/examples/industrial_data_pretraining/sense_voice/CONTINUAL_FINETUNING.md b/examples/industrial_data_pretraining/sense_voice/CONTINUAL_FINETUNING.md
index 86679756ab..6ca898eea5 100644
--- a/examples/industrial_data_pretraining/sense_voice/CONTINUAL_FINETUNING.md
+++ b/examples/industrial_data_pretraining/sense_voice/CONTINUAL_FINETUNING.md
@@ -24,16 +24,19 @@ relative regression = (candidate CER - baseline CER) / baseline CER
 The threshold is a product decision, not a FunASR guarantee. Select a checkpoint
 only when it meets every retention threshold and the new-domain target.
 
-A real starting point from [issue #3388](https://github.com/modelscope/FunASR/issues/3388)
-is:
-
-| Validation set | Utterances | Baseline CER |
-| --- | ---: | ---: |
-| Mandarin FLEURS test | 300 | 8.9% |
-| Cantonese ASCEND dialogue | 314 | 9.1% |
-| Teochew held-out, about 20 speakers in the source corpus | 300 | 93.3% |
-
-Keep the Teochew held-out speakers out of the 8.45-hour training set.
+References must be independently audited for transcription policy and provenance.
+Check whether new-domain labels are verbatim transcripts or written-language
+paraphrases, and whether test references were generated by the same process as
+training labels. Speaker separation alone does not make those references reliable.
+An unaudited new-domain CER must not select checkpoints or tune replay ratios.
+
+The reporter in [issue #3388](https://github.com/modelscope/FunASR/issues/3388#issuecomment-5578763142)
+later withdrew the earlier new-domain evaluation and rebuilt an independent test
+set. The old baseline table is therefore not a valid selection reference. Recompute
+the frozen baseline and all candidates with the same reviewed references and CER
+normalization. For Mandarin and Cantonese, also separate read and spontaneous
+speech when both matter in production. Keep held-out speakers out of the 8.45-hour
+training example below; its replay budgets are illustrative, not validated optima.
 
 ## 2. Build a replay manifest
 
@@ -72,15 +75,29 @@ pool totals disagree.
 
 ## 3. Use a supported language token
 
-SenseVoiceSmall currently has a closed language-id set: `<|zh|>`, `<|en|>`,
-`<|yue|>`, `<|ja|>`, and `<|ko|>`. For Teochew transcripts written as
-standard Chinese, use `<|zh|>` for the first experiment.
+The current model's named inference language mapping includes `zh`, `en`, `yue`,
+`ja`, and `ko` (plus automatic/no-speech handling). This is not the complete
+tokenizer vocabulary. Sharing `<|zh|>` with a new domain is an experiment, not an
+isolation mechanism: it can interfere with Mandarin and must pass retention gates.
+
+The #3388 reporter found a useful `<|minnan|>` comparison in their setup. A token
+existing in a vocabulary does not mean it is unused, freely repurposable, or
+accepted by the stock inference language mapping. Pin the tokenizer/model revision
+and inspect the token id, training target and query embedding path, and inference
+mapping before adopting a language-tag change. Do not generalize that experiment
+into a guarantee for another language or checkpoint.
 
 Do not add `<|teochew|>` to the JSONL and assume it becomes a new language id.
 The current tokenizer does not encode it as one supported special token. A real
 custom language id requires coordinated tokenizer, vocabulary, language
 embedding, checkpoint migration, export, and inference changes.
 
+Check downstream language validation and every allowlist as well. Test an actual
+result through export, service parsing and the final client: a valid model result
+must not be silently discarded because its language tag is unfamiliar. Preserve
+raw model output while diagnosing an empty response; do not simply disable all
+validation or relabel the result to pass a closed list.
+
 ## 4. Train in two stages
 
 Copy `finetune.sh` to an experiment directory, point it at the mixed training
@@ -129,6 +146,31 @@ parameters trainable because no parameter name matches it.
 
 ## 5. Select the checkpoint by constraints
 
+The maintained `finetune.sh` explicitly uses:
+
+```bash
+++train_conf.avg_keep_nbest_models_type=loss
+```
+
+SenseVoice returns ASR CTC loss plus a rich-tag objective and `acc_rich`, not the
+trainer's ASR `acc`. `acc_rich` is not CER or ASR accuracy. A missing metric must not
+be treated as a real zero; genuine `acc=0` remains a valid score for models that
+actually report it. The trainers exclude an unavailable/nonfinite selected metric
+from best selection, keep-N ranking and metric-based averaging, with an explicit
+warning. This can leave unranked checkpoints on disk; correct the criterion/data
+instead of assuming the keep-N limit applies to them.
+
+Use a new output directory when changing from accuracy to loss ranking. Resuming
+with a different criterion is rejected; old zero-valued histories cannot reliably
+be identified as missing after the fact, and pruned weights cannot be recovered.
+Earlier runs affected by this defect need independent reevaluation of retained
+checkpoints, not just an upgrade. Revalidation cannot overwrite the current best
+under the same checkpoint name if its selected metric becomes unavailable.
+
+`model.pt.best` now means best **total validation loss** for this recipe, not the
+lowest CER or best retained-language behavior. Weight averaging is also only a
+candidate: reevaluate the averaged model under all the same gates.
+
 Evaluate every candidate checkpoint on Mandarin, Cantonese, and Teochew
 separately.
 
@@ -156,6 +198,8 @@ Verify the trainable parameter list before relying on any adapter experiment.
 - Baseline CER/WER and acceptable relative regression are recorded per language.
 - Pseudo-labels are filtered and manually sampled for audit.
 - Replay is sampled to an explicit per-epoch budget with a Cantonese floor.
-- Teochew uses the supported `<|zh|>` path unless the model is deliberately forked.
+- References and normalization are independently audited before any CER comparison.
+- Language-token mapping and downstream allowlists pass an end-to-end result check.
+- The ranking metric is explicit; changed criteria use a new output directory.
 - Freeze logs and trainable parameters match the intended stage.
 - Every saved checkpoint is evaluated on all retained and new domains.
diff --git a/examples/industrial_data_pretraining/sense_voice/CONTINUAL_FINETUNING_zh.md b/examples/industrial_data_pretraining/sense_voice/CONTINUAL_FINETUNING_zh.md
index 6264d73602..5cf26b0587 100644
--- a/examples/industrial_data_pretraining/sense_voice/CONTINUAL_FINETUNING_zh.md
+++ b/examples/industrial_data_pretraining/sense_voice/CONTINUAL_FINETUNING_zh.md
@@ -20,15 +20,15 @@ replay 数据之间必须说话人不重叠。不要用一个混合 CER 选择 c
 阈值应由业务要求决定，不是 FunASR 的保证值。候选 checkpoint 必须同时满足所有旧语种
 阈值和新域目标。
 
-[issue #3388](https://github.com/modelscope/FunASR/issues/3388) 提供了一个真实起点：
+参考文本的标注规范和来源必须经过独立核验：新域标签是逐字转写还是书面语意译？测试
+参考是否与训练标签来自同一套生成流程？仅做到说话人不重叠，并不能证明标注可靠。
+未经核验的新域 CER 不能用来选 checkpoint，也不能用来调整 replay 比例。
 
-| 验证集 | 句数 | 基线 CER |
-| --- | ---: | ---: |
-| 普通话 FLEURS test | 300 | 8.9% |
-| 粤语 ASCEND 口语对话 | 314 | 9.1% |
-| 潮汕话 held-out（源语料约 20 名说话人） | 300 | 93.3% |
-
-潮汕话 held-out 中的说话人不能出现在 8.45 小时训练数据中。
+[issue #3388 的后续反馈](https://github.com/modelscope/FunASR/issues/3388#issuecomment-5578763142)
+已撤回早期新域评测，改用另建的独立测试集。因此旧基线表不能继续作为选点依据。
+应使用相同、经过人工复核的参考文本和 CER 归一化规则，重新评测原模型及所有候选。
+线上同时包含朗读和自发口语时，普通话、粤语也应分别检查这两类数据。下文 8.45 小时
+训练示例仍须排除 held-out 说话人；其 replay 小时数是预算演示，不是已验证的最优值。
 
 ## 2. 构建 replay 清单
 
@@ -61,13 +61,23 @@ replay 数据之间必须说话人不重叠。不要用一个混合 CER 选择 c
 
 ## 3. 使用现有支持的语言 token
 
-SenseVoiceSmall 当前语言 id 是闭集：`<|zh|>`、`<|en|>`、`<|yue|>`、
-`<|ja|>` 和 `<|ko|>`。潮汕话转写目标为标准中文时，第一轮实验使用 `<|zh|>`。
+当前模型具名推理语言映射包含 `zh`、`en`、`yue`、`ja`、`ko`，以及自动判断和无语音
+处理；这不是 tokenizer 完整词表。让新域共享 `<|zh|>` 只是实验方案，不是隔离机制，
+可能干扰普通话，必须通过旧域保持评测。
+
+#3388 报告者在自己的设置中获得了有价值的 `<|minnan|>` 对照结果，但“词表中存在”
+不等于“空闲、可任意复用”，也不代表原版推理语言映射支持它。采用语言 tag 改动前，
+固定 tokenizer/模型版本，核对 token id、训练目标和查询 embedding 路径以及推理映射。
+不能把该个例写成其他语种或 checkpoint 的保证。
 
 不要直接在 JSONL 中添加 `<|teochew|>` 并假设它会成为新语言 id。当前 tokenizer
 不会把它编码成一个受支持的特殊 token。真正新增自定义语言 id，需要同步修改 tokenizer、
 词表、language embedding、旧权重迁移、导出和推理代码。
 
+还要检查下游语言校验与每一处白名单，用真实结果走通导出、服务端解析和最终客户端。
+不能因为语言 tag 不在旧枚举中，就静默丢弃有效的模型输出。排查空响应时保留原始模型
+结果，不要简单关闭全部校验或改写语言标签来绕过白名单。
+
 ## 4. 分两阶段训练
 
 把 `finetune.sh` 复制到实验目录，指向混合训练 manifest 和固定验证集，然后把默认的
@@ -110,6 +120,26 @@ Setting encoder...requires_grad = False
 
 ## 5. 按约束选择 checkpoint
 
+维护中的 `finetune.sh` 已明确指定：
+
+```bash
+++train_conf.avg_keep_nbest_models_type=loss
+```
+
+SenseVoice 返回 ASR CTC loss 与 rich-tag 目标，以及 `acc_rich`，并不返回训练器所选的
+ASR `acc`。`acc_rich` 不是 CER 或 ASR 准确率。缺失指标不能伪装成真实零值；对确实
+返回准确率的模型，`acc=0` 仍是有效值。所选指标缺失、非有限值或只覆盖部分 batch/rank
+时，训练器会明确告警，并将该点排除在 best、keep-N 排名和按指标平均之外。未参与排名
+的 checkpoint 可能继续留在磁盘上，应修正指标或数据，不要假设 keep-N 会删除它们。
+
+从 accuracy 改为 loss 排名时，必须使用新的输出目录；恢复时混用两套指标会被拒绝。
+历史上的零值无法可靠追溯为“缺失”，已裁剪的权重也无法恢复。受影响的旧训练需要对
+仍保留的 checkpoint 独立复测，而不是只升级软件。同名重验若导致当前 best 的所选指标
+失效，也会被拒绝，避免覆盖现有 best。
+
+这个配方的 `model.pt.best` 表示**总验证 loss 最优**，不是 CER 最低或旧域保持最好。
+权重平均结果也只是候选模型，仍须重新通过全部评测门槛。
+
 每个候选 checkpoint 都要分别评估普通话、粤语和潮汕话。
 
 1. 丢弃任何一个旧语种超过退化阈值的 checkpoint。
@@ -133,6 +163,8 @@ SenseVoice adapter；任何 adapter 实验都必须先核对实际可训练参
 - 已记录每个语种的基线 CER/WER 和可接受相对退化。
 - 已过滤伪标签，并按语种和说话人做人工抽检。
 - replay 使用明确的每轮预算，并设置粤语最低占比。
-- 未 fork 模型时，潮汕话使用当前支持的 `<|zh|>` 路径。
+- 参考文本和归一化规则已经独立核验，再做 CER 对比。
+- 语言 token 映射和下游白名单已经完成真实结果的端到端检查。
+- 已明确排名指标；更换指标时使用新的输出目录。
 - 冻结日志和可训练参数与当前阶段一致。
 - 所有保存的 checkpoint 都分别评估旧语种和新域。
diff --git a/examples/industrial_data_pretraining/sense_voice/finetune.sh b/examples/industrial_data_pretraining/sense_voice/finetune.sh
index 081b77b016..5867d93b70 100644
--- a/examples/industrial_data_pretraining/sense_voice/finetune.sh
+++ b/examples/industrial_data_pretraining/sense_voice/finetune.sh
@@ -63,6 +63,7 @@ ${train_tool} \
 ++train_conf.save_checkpoint_interval=2000 \
 ++train_conf.keep_nbest_models=20 \
 ++train_conf.avg_nbest_model=10 \
+++train_conf.avg_keep_nbest_models_type=loss \
 ++train_conf.use_deepspeed=false \
 ++train_conf.deepspeed_config=${deepspeed_config} \
 ++optim_conf.lr=0.0002 \
diff --git a/funasr/train_utils/average_nbest_models.py b/funasr/train_utils/average_nbest_models.py
index 873f4192c1..5517903db3 100644
--- a/funasr/train_utils/average_nbest_models.py
+++ b/funasr/train_utils/average_nbest_models.py
@@ -14,6 +14,7 @@
 import re
 from collections import OrderedDict
 from functools import cmp_to_key
+from funasr.train_utils.checkpoint_metrics import finite_scalar
 
 
 def _get_checkpoint_paths(output_dir: str, last_n: int = 5, use_deepspeed=False, **kwargs):
@@ -31,7 +32,19 @@ def _get_checkpoint_paths(output_dir: str, last_n: int = 5, use_deepspeed=False,
             )
         avg_keep_nbest_models_type = checkpoint["avg_keep_nbest_models_type"]
         val_step_or_epoch = checkpoint[f"val_{avg_keep_nbest_models_type}_step_or_epoch"]
-        sorted_items = sorted(val_step_or_epoch.items(), key=lambda x: x[1], reverse=True)
+        eligible = []
+        for key, value in val_step_or_epoch.items():
+            value = finite_scalar(value)
+            ckpt = os.path.join(output_dir, key)
+            if use_deepspeed:
+                ckpt = os.path.join(ckpt, "mp_rank_00_model_states.pt")
+            if value is not None and os.path.isfile(ckpt):
+                eligible.append((key, value))
+        if not eligible:
+            logging.warning("No checkpoints with an available finite %s metric for averaging.",
+                            avg_keep_nbest_models_type)
+            return []
+        sorted_items = sorted(eligible, key=lambda x: x[1], reverse=True)
         sorted_items = (
             sorted_items[:last_n] if avg_keep_nbest_models_type == "acc" else sorted_items[-last_n:]
         )
@@ -43,8 +56,8 @@ def _get_checkpoint_paths(output_dir: str, last_n: int = 5, use_deepspeed=False,
                 ckpt = os.path.join(output_dir, key, "mp_rank_00_model_states.pt")
             checkpoint_paths.append(ckpt)
 
-    except:
-        print(f"{checkpoint} does not exist, avg the lastet checkpoint.")
+    except (FileNotFoundError, KeyError):
+        logging.warning("Checkpoint ranking metadata unavailable; averaging latest checkpoints.")
         # List all files in the output directory
         files = os.listdir(output_dir)
         # Filter out checkpoint files and extract epoch numbers
diff --git a/funasr/train_utils/checkpoint_metrics.py b/funasr/train_utils/checkpoint_metrics.py
new file mode 100644
index 0000000000..a567e93a2f
--- /dev/null
+++ b/funasr/train_utils/checkpoint_metrics.py
@@ -0,0 +1,99 @@
+"""Validation metric availability shared by the torch and DeepSpeed trainers."""
+
+import logging
+import math
+
+import torch
+import torch.distributed as dist
+
+
+def finite_scalar(value):
+    if isinstance(value, torch.Tensor):
+        if value.numel() != 1:
+            return None
+        value = value.detach().item()
+    try:
+        value = float(value)
+    except (TypeError, ValueError):
+        return None
+    return value if math.isfinite(value) else None
+
+
+class ValidationMetrics:
+    def __init__(self):
+        self.count = 0
+        self.sums = {"loss": 0.0, "acc": 0.0}
+        self.complete = {"loss": True, "acc": True}
+
+    def update(self, loss, stats):
+        loss = finite_scalar(loss)
+        values = {"loss": loss, "acc": finite_scalar(stats.get("acc"))}
+        self.count += 1
+        for name, value in values.items():
+            if value is None or loss is None:
+                self.complete[name] = False
+            else:
+                self.sums[name] += value
+
+    def compute(self, device, distributed=False):
+        names = ("loss", "acc")
+        means = [self.sums[name] / max(self.count, 1) for name in names]
+        available = [self.count > 0 and self.complete[name] for name in names]
+        if distributed:
+            # All ranks enter both collectives, including empty/nonfinite ranks.
+            values = torch.tensor(means, dtype=torch.float32, device=device)
+            flags = torch.tensor(available, dtype=torch.int32, device=device)
+            dist.all_reduce(values, op=dist.ReduceOp.SUM)
+            dist.all_reduce(flags, op=dist.ReduceOp.MIN)
+            means = (values / dist.get_world_size()).cpu().tolist()
+            available = flags.cpu().tolist()
+        return {
+            name: finite_scalar(value) if valid else None
+            for name, value, valid in zip(names, means, available)
+        }
+
+
+def record_validation_metrics(trainer, ckpt_name, metrics):
+    selected = trainer.avg_keep_nbest_models_type
+    reject = metrics[selected] is None and trainer.best_step_or_epoch == ckpt_name
+    distributed = trainer.use_ddp or trainer.use_fsdp or getattr(trainer, "use_deepspeed", False)
+    if metrics[selected] is None and distributed:
+        # Only rank zero may have updated best during checkpoint saving.
+        flag = torch.tensor(int(reject), dtype=torch.int32, device=trainer.device)
+        dist.all_reduce(flag, op=dist.ReduceOp.MAX)
+        reject = bool(flag.item())
+    if reject:
+        raise ValueError(
+            f"Cannot overwrite current best checkpoint {ckpt_name} with unavailable "
+            f"validation {selected}; use a new checkpoint name or output directory."
+        )
+    for name, value in metrics.items():
+        setattr(trainer, f"val_{name}_avg", value if value is not None else float("nan"))
+        history = getattr(trainer, f"val_{name}_step_or_epoch")
+        if value is None:
+            history.pop(ckpt_name, None)
+        else:
+            history[ckpt_name] = value
+    if metrics[selected] is None:
+        trainer.saved_ckpts.pop(ckpt_name, None)
+        if trainer.rank == 0 and not trainer._warned_validation_metric:
+            remedy = (
+                " For models without ASR accuracy, start a new output directory with "
+                "++train_conf.avg_keep_nbest_models_type=loss; acc_rich is not ASR accuracy."
+                if selected == "acc" else " Check the validation data and model outputs."
+            )
+            logging.warning(
+                "Validation has no complete, finite %s metric on every batch/rank; "
+                "this checkpoint is excluded from best, pruning and averaging.%s",
+                selected, remedy,
+            )
+            trainer._warned_validation_metric = True
+
+
+def check_resume_ranking(checkpoint, configured):
+    previous = checkpoint.get("avg_keep_nbest_models_type")
+    if previous is not None and previous != configured:
+        raise ValueError(
+            f"Cannot change checkpoint ranking metric from {previous} to {configured} "
+            "while resuming. Use a new output directory to avoid mixing metric histories."
+        )
diff --git a/funasr/train_utils/trainer.py b/funasr/train_utils/trainer.py
index b0493c03f3..38acf3fb75 100644
--- a/funasr/train_utils/trainer.py
+++ b/funasr/train_utils/trainer.py
@@ -13,6 +13,9 @@
 from funasr.train_utils.device_funcs import to_device
 from funasr.train_utils.recursive_op import recursive_average
 from funasr.train_utils.average_nbest_models import average_checkpoints
+from funasr.train_utils.checkpoint_metrics import (
+    ValidationMetrics, check_resume_ranking, record_validation_metrics,
+)
 from torch.distributed.fsdp.sharded_grad_scaler import ShardedGradScaler
 
 try:
@@ -127,6 +130,7 @@ def __init__(
         self.best_step_or_epoch = ""
         self.val_acc_step_or_epoch = {}
         self.val_loss_step_or_epoch = {}
+        self._warned_validation_metric = False
 
         self.reset_gpu_cache = kwargs.get("reset_gpu_cache", False)
         self.start_data_split_i = 0
@@ -202,11 +206,9 @@ def save_checkpoint(
             else:
                 ckpt_name = f"model.pt.ep{epoch}.{step}"
             filename = os.path.join(self.output_dir, ckpt_name)
-            torch.save(state, filename)
-            logging.info(f"Checkpoint saved to {filename}")
-
             latest = Path(os.path.join(self.output_dir, f"model.pt"))
-            torch.save(state, latest)
+            write_best = False
+            prune_path = None
 
             if self.best_step_or_epoch == "" and ckpt_name in getattr(
                 self, f"val_{self.avg_keep_nbest_models_type}_step_or_epoch"
@@ -219,7 +221,7 @@ def save_checkpoint(
                 if cur_acc is not None and (best_acc is None or cur_acc >= best_acc):
                     self.best_step_or_epoch = ckpt_name
                     best_ckpt = Path(os.path.join(self.output_dir, f"model.pt.best"))
-                    torch.save(state, best_ckpt)
+                    write_best = True
                     logging.info(
                         f"Update best acc: {cur_acc:.4f}, {best_ckpt}"
                     )
@@ -237,7 +239,7 @@ def save_checkpoint(
                 if cur_loss is not None and (best_loss is None or cur_loss <= best_loss):
                     self.best_step_or_epoch = ckpt_name
                     best_ckpt = Path(os.path.join(self.output_dir, f"model.pt.best"))
-                    torch.save(state, best_ckpt)
+                    write_best = True
                     logging.info(
                         f"Update best loss: {cur_loss:.4f}, {best_ckpt}"
                     )
@@ -276,10 +278,19 @@ def save_checkpoint(
                             key = max(self.saved_ckpts, key=self.saved_ckpts.get)
                         if key in self.saved_ckpts:
                             del self.saved_ckpts[key]
-                        filename = os.path.join(self.output_dir, key)
-                        logging.info(f"Delete: {filename}")
-                        if os.path.exists(filename):
-                            os.remove(filename)
+                        prune_path = os.path.join(self.output_dir, key)
+
+            state["best_step_or_epoch"] = self.best_step_or_epoch
+            state["saved_ckpts"] = dict(self.saved_ckpts)
+            torch.save(state, filename)
+            torch.save(state, latest)
+            if write_best:
+                torch.save(state, best_ckpt)
+            logging.info(f"Checkpoint saved to {filename}")
+            # Do not delete a previous candidate before all new writes succeed.
+            if prune_path is not None and os.path.exists(prune_path):
+                logging.info(f"Delete: {prune_path}")
+                os.remove(prune_path)
 
         if self.use_ddp or self.use_fsdp:
             dist.barrier()
@@ -302,6 +313,7 @@ def resume_checkpoint(
             ckpt = os.path.join(self.output_dir, "model.pt")
             if os.path.isfile(ckpt):
                 checkpoint = torch.load(ckpt, map_location="cpu")
+                check_resume_ranking(checkpoint, self.avg_keep_nbest_models_type)
                 self.start_epoch = checkpoint["epoch"]
                 # self.model.load_state_dict(checkpoint['state_dict'])
                 src_state = checkpoint["state_dict"]
@@ -580,6 +592,7 @@ def validate_epoch(
             dist.barrier()
         logging.info(f"Validate epoch: {epoch}, rank: {self.rank}\n")
         model.eval()
+        metrics = ValidationMetrics()
 
         with torch.no_grad():
 
@@ -620,27 +633,10 @@ def validate_epoch(
                 loss = loss
                 time4 = time.perf_counter()
 
-                if torch.isfinite(loss):
-                    self.val_loss_avg = (
-                        self.val_loss_avg * batch_idx + loss.detach().cpu().item()
-                    ) / (batch_idx + 1)
-
-                    if "acc" in stats:
-                        self.val_acc_avg = (
-                            self.val_acc_avg * batch_idx + stats["acc"].detach().cpu().item()
-                        ) / (batch_idx + 1)
-
-                    if self.use_ddp or self.use_fsdp:
-                        val_loss_avg = torch.tensor(self.val_loss_avg, dtype=torch.float32).to(
-                            self.device
-                        )
-                        val_acc_avg = torch.tensor(self.val_acc_avg, dtype=torch.float32).to(
-                            self.device
-                        )
-                        dist.all_reduce(val_loss_avg, op=dist.ReduceOp.SUM)
-                        dist.all_reduce(val_acc_avg, op=dist.ReduceOp.SUM)
-                        self.val_loss_avg = val_loss_avg.detach().cpu().item() / self.world_size
-                        self.val_acc_avg = val_acc_avg.detach().cpu().item() / self.world_size
+                metrics.update(loss, stats)
+                running = metrics.compute(self.device)
+                self.val_loss_avg = running["loss"] if running["loss"] is not None else float("nan")
+                self.val_acc_avg = running["acc"] if running["acc"] is not None else float("nan")
 
                 time5 = time.perf_counter()
                 batch_num_epoch = 1
@@ -667,8 +663,10 @@ def validate_epoch(
             ckpt_name = f"model.pt.ep{epoch}"
         else:
             ckpt_name = f'model.pt.ep{epoch}.{kwargs.get("step_in_epoch")}'
-        self.val_acc_step_or_epoch[ckpt_name] = self.val_acc_avg
-        self.val_loss_step_or_epoch[ckpt_name] = self.val_loss_avg
+        record_validation_metrics(
+            self, ckpt_name,
+            metrics.compute(self.device, distributed=self.use_ddp or self.use_fsdp),
+        )
         model.train()
 
         if self.use_ddp or self.use_fsdp:
diff --git a/funasr/train_utils/trainer_ds.py b/funasr/train_utils/trainer_ds.py
index 9bd7ca31ea..fc2f2b660f 100644
--- a/funasr/train_utils/trainer_ds.py
+++ b/funasr/train_utils/trainer_ds.py
@@ -14,6 +14,9 @@
 from funasr.train_utils.device_funcs import to_device
 from funasr.train_utils.recursive_op import recursive_average
 from funasr.train_utils.average_nbest_models import average_checkpoints
+from funasr.train_utils.checkpoint_metrics import (
+    ValidationMetrics, check_resume_ranking, record_validation_metrics,
+)
 from torch.distributed.fsdp.sharded_grad_scaler import ShardedGradScaler
 import funasr.utils.misc as misc_utils
 
@@ -129,6 +132,7 @@ def __init__(
         self.best_step_or_epoch = ""
         self.val_acc_step_or_epoch = {}
         self.val_loss_step_or_epoch = {}
+        self._warned_validation_metric = False
 
         self.reset_gpu_cache = kwargs.get("reset_gpu_cache", False)
         self.start_data_split_i = 0
@@ -226,14 +230,8 @@ def save_checkpoint(
                 ckpt_name = f"model.pt.ep{epoch}.{step}"
             filename = os.path.join(self.output_dir, ckpt_name)
 
-            # torch.save(state, filename)
-            with torch.no_grad():
-                model.save_checkpoint(save_dir=self.output_dir, tag=ckpt_name, client_state=state)
-            logging.info(f"\nCheckpoint saved to {filename}\n")
-            latest = Path(os.path.join(self.output_dir, f"model.pt"))
-            # torch.save(state, latest)
-            with torch.no_grad():
-                model.save_checkpoint(save_dir=self.output_dir, tag=f"model.pt", client_state=state)
+            write_best = False
+            prune_path = None
             if self.best_step_or_epoch == "" and ckpt_name in getattr(
                 self, f"val_{self.avg_keep_nbest_models_type}_step_or_epoch"
             ):
@@ -245,11 +243,7 @@ def save_checkpoint(
                 if cur_acc is not None and (best_acc is None or cur_acc >= best_acc):
                     self.best_step_or_epoch = ckpt_name
                     best_ckpt = Path(os.path.join(self.output_dir, f"model.pt.best"))
-                    # torch.save(state, best_ckpt)
-                    with torch.no_grad():
-                        model.save_checkpoint(
-                            save_dir=self.output_dir, tag=f"model.pt.best", client_state=state
-                        )
+                    write_best = True
                     logging.info(
                         f"Update best acc: {cur_acc:.4f}, {best_ckpt}"
                     )
@@ -267,11 +261,7 @@ def save_checkpoint(
                 if cur_loss is not None and (best_loss is None or cur_loss <= best_loss):
                     self.best_step_or_epoch = ckpt_name
                     best_ckpt = Path(os.path.join(self.output_dir, f"model.pt.best"))
-                    # torch.save(state, best_ckpt)
-                    with torch.no_grad():
-                        model.save_checkpoint(
-                            save_dir=self.output_dir, tag=f"model.pt.best", client_state=state
-                        )
+                    write_best = True
                     logging.info(
                         f"Update best loss: {cur_loss:.4f}, {best_ckpt}"
                     )
@@ -311,11 +301,24 @@ def save_checkpoint(
                                 key = max(self.saved_ckpts, key=self.saved_ckpts.get)
                             if key in self.saved_ckpts:
                                 del self.saved_ckpts[key]
-                            filename = os.path.join(self.output_dir, key)
-                            logging.info(f"Delete: {filename}")
-                            if os.path.exists(filename):
-                                # os.remove(filename)
-                                misc_utils.smart_remove(filename)
+                            prune_path = os.path.join(self.output_dir, key)
+
+            if dist.is_initialized():
+                # Ranking is owned by rank zero; engine writes remain collective.
+                decision = [(self.best_step_or_epoch, self.saved_ckpts, write_best)]
+                dist.broadcast_object_list(decision, src=0)
+                self.best_step_or_epoch, self.saved_ckpts, write_best = decision[0]
+            state["best_step_or_epoch"] = self.best_step_or_epoch
+            state["saved_ckpts"] = dict(self.saved_ckpts)
+            with torch.no_grad():
+                model.save_checkpoint(save_dir=self.output_dir, tag=ckpt_name, client_state=state)
+                model.save_checkpoint(save_dir=self.output_dir, tag="model.pt", client_state=state)
+                if write_best:
+                    model.save_checkpoint(save_dir=self.output_dir, tag="model.pt.best", client_state=state)
+            logging.info(f"Checkpoint saved to {filename}")
+            if self.rank == 0 and prune_path is not None and os.path.exists(prune_path):
+                logging.info(f"Delete: {prune_path}")
+                misc_utils.smart_remove(prune_path)
 
         elif self.use_fsdp:
             raise NotImplementedError(
@@ -373,11 +376,9 @@ def save_checkpoint(
             else:
                 ckpt_name = f"model.pt.ep{epoch}.{step}"
             filename = os.path.join(self.output_dir, ckpt_name)
-            torch.save(state, filename)
-
-            logging.info(f"\nCheckpoint saved to {filename}\n")
             latest = Path(os.path.join(self.output_dir, f"model.pt"))
-            torch.save(state, latest)
+            write_best = False
+            prune_path = None
             if self.best_step_or_epoch == "" and ckpt_name in getattr(
                 self, f"val_{self.avg_keep_nbest_models_type}_step_or_epoch"
             ):
@@ -389,7 +390,7 @@ def save_checkpoint(
                 if cur_acc is not None and (best_acc is None or cur_acc >= best_acc):
                     self.best_step_or_epoch = ckpt_name
                     best_ckpt = Path(os.path.join(self.output_dir, f"model.pt.best"))
-                    torch.save(state, best_ckpt)
+                    write_best = True
                     logging.info(
                         f"Update best acc: {cur_acc:.4f}, {best_ckpt}"
                     )
@@ -407,7 +408,7 @@ def save_checkpoint(
                 if cur_loss is not None and (best_loss is None or cur_loss <= best_loss):
                     self.best_step_or_epoch = ckpt_name
                     best_ckpt = Path(os.path.join(self.output_dir, f"model.pt.best"))
-                    torch.save(state, best_ckpt)
+                    write_best = True
                     logging.info(
                         f"Update best loss: {cur_loss:.4f}, {best_ckpt}"
                     )
@@ -446,11 +447,18 @@ def save_checkpoint(
                             key = max(self.saved_ckpts, key=self.saved_ckpts.get)
                         if key in self.saved_ckpts:
                             del self.saved_ckpts[key]
-                        filename = os.path.join(self.output_dir, key)
-                        logging.info(f"Delete: {filename}")
-                        if os.path.exists(filename):
-                            # os.remove(filename)
-                            misc_utils.smart_remove(filename)
+                        prune_path = os.path.join(self.output_dir, key)
+
+            state["best_step_or_epoch"] = self.best_step_or_epoch
+            state["saved_ckpts"] = dict(self.saved_ckpts)
+            torch.save(state, filename)
+            torch.save(state, latest)
+            if write_best:
+                torch.save(state, best_ckpt)
+            logging.info(f"Checkpoint saved to {filename}")
+            if prune_path is not None and os.path.exists(prune_path):
+                logging.info(f"Delete: {prune_path}")
+                misc_utils.smart_remove(prune_path)
 
         if self.use_ddp or self.use_fsdp:
             dist.barrier()
@@ -475,6 +483,7 @@ def resume_checkpoint(
                 ckpt = os.path.join(self.output_dir, "model.pt")
                 if os.path.exists(ckpt):
                     _, checkpoint = model.load_checkpoint(self.output_dir, "model.pt")
+                    check_resume_ranking(checkpoint, self.avg_keep_nbest_models_type)
                     self.start_epoch = checkpoint["epoch"]
                     self.saved_ckpts = checkpoint["saved_ckpts"]
                     self.val_acc_step_or_epoch = (
@@ -520,6 +529,7 @@ def resume_checkpoint(
                 ckpt = os.path.join(self.output_dir, "model.pt")
                 if os.path.isfile(ckpt):
                     checkpoint = torch.load(ckpt, map_location="cpu")
+                    check_resume_ranking(checkpoint, self.avg_keep_nbest_models_type)
                     self.start_epoch = checkpoint["epoch"]
                     # self.model.load_state_dict(checkpoint['state_dict'])
                     src_state = checkpoint["state_dict"]
@@ -812,8 +822,7 @@ def validate_epoch(
         Args:
             epoch (int): The current epoch number.
         """
-        self.val_loss_avg = 0.0
-        self.val_acc_avg  = 0.0
+        metrics = ValidationMetrics()
 
         if self.use_ddp or self.use_fsdp or self.use_deepspeed:
             dist.barrier()
@@ -860,31 +869,23 @@ def validate_epoch(
 
                 loss_dict["batch_num_epoch"] = len(dataloader_val)
 
+                metrics.update(loss_dict["loss"], loss_dict["stats"])
+                running = metrics.compute(self.device)
+                self.val_loss_avg = running["loss"] if running["loss"] is not None else float("nan")
+                self.val_acc_avg = running["acc"] if running["acc"] is not None else float("nan")
                 self.log(loss_dict, tag="val")
                 time_beg = time.perf_counter()
-                self.val_loss_avg = (
-                    self.val_loss_avg * batch_idx + loss_dict["loss"].detach().cpu().item()
-                ) / (batch_idx + 1)
-                if "acc" in loss_dict["stats"]:
-                    self.val_acc_avg = (
-                        self.val_acc_avg * batch_idx
-                        + loss_dict["stats"]["acc"].detach().cpu().item()
-                    ) / (batch_idx + 1)
-
-            if self.use_ddp or self.use_fsdp or self.use_deepspeed:
-                val_loss_avg = torch.tensor(self.val_loss_avg, dtype=torch.float32).to(self.device)
-                val_acc_avg = torch.tensor(self.val_acc_avg, dtype=torch.float32).to(self.device)
-                dist.all_reduce(val_loss_avg, op=dist.ReduceOp.SUM)
-                dist.all_reduce(val_acc_avg, op=dist.ReduceOp.SUM)
-                self.val_loss_avg = val_loss_avg.detach().cpu().item() / self.world_size
-                self.val_acc_avg = val_acc_avg.detach().cpu().item() / self.world_size
 
         if kwargs.get("step_in_epoch", None) is None:
             ckpt_name = f"model.pt.ep{epoch}"
         else:
             ckpt_name = f'model.pt.ep{epoch}.{kwargs.get("step_in_epoch")}'
-        self.val_acc_step_or_epoch[ckpt_name] = self.val_acc_avg
-        self.val_loss_step_or_epoch[ckpt_name] = self.val_loss_avg
+        record_validation_metrics(
+            self, ckpt_name,
+            metrics.compute(
+                self.device, distributed=self.use_ddp or self.use_fsdp or self.use_deepspeed
+            ),
+        )
 
         if self.use_ddp or self.use_fsdp or self.use_deepspeed:
             dist.barrier()
diff --git a/tests/test_checkpoint_metric_distributed.py b/tests/test_checkpoint_metric_distributed.py
new file mode 100644
index 0000000000..cf6d76689e
--- /dev/null
+++ b/tests/test_checkpoint_metric_distributed.py
@@ -0,0 +1,86 @@
+"""Actual two-rank CPU collectives; no distributed acoustic training claim."""
+
+from datetime import timedelta
+import json
+from pathlib import Path
+import time
+
+import pytest
+import torch.distributed as dist
+import torch.multiprocessing as mp
+
+from test_checkpoint_metric_presence import Run
+
+
+def _validate_worker(rank, root):
+    root = Path(root)
+    dist.init_process_group("gloo", rank=rank, world_size=2,
+                            init_method=(root / "gloo-init").as_uri(),
+                            timeout=timedelta(seconds=30))
+    results = {}
+    try:
+        for kind in ("torch", "ds_torch", "ds_engine"):
+            for case in ("valid", "missing", "nonfinite", "empty", "reject_best"):
+                run = Run(root / f"{kind}-{case}-{rank}", kind)
+                run.trainer.rank = rank
+                run.trainer.world_size = 2
+                run.trainer.use_ddp = True
+                values = ([(1.0, 0.2), (3.0, 0.4)] if rank == 0 else
+                          [(3.0, 0.6), (5.0, 0.8)])
+                if rank == 1 and case == "missing":
+                    values[-1] = (5.0, "missing")
+                if rank == 1 and case == "nonfinite":
+                    values[-1] = (float("nan"), 0.8)
+                if rank == 1 and case == "empty":
+                    values = []
+                try:
+                    run.validate(1, values)
+                    if case == "reject_best":
+                        run.save(1)
+                        if kind == "ds_engine":
+                            assert run.trainer.saved_ckpts == {"model.pt.ep1": pytest.approx(0.5)}
+                            assert run.checkpoint("model.pt")["saved_ckpts"] == run.trainer.saved_ckpts
+                        before = dict(run.trainer.val_acc_step_or_epoch)
+                        rejected = False
+                        try:
+                            run.validate(1, [(1.0, "missing")])
+                        except ValueError as error:
+                            rejected = "current best" in str(error)
+                        results[f"{kind}-reject_best"] = {
+                            "rejected": rejected,
+                            "unchanged": before == run.trainer.val_acc_step_or_epoch,
+                        }
+                        continue
+                    results[f"{kind}-{case}"] = {
+                        "acc": run.trainer.val_acc_step_or_epoch,
+                        "loss": run.trainer.val_loss_step_or_epoch,
+                    }
+                finally:
+                    run.close()
+        (root / f"rank-{rank}.json").write_text(json.dumps(results))
+    finally:
+        dist.destroy_process_group()
+
+
+def test_distributed_validation_agrees_on_availability_and_valid_means(tmp_path):
+    assert dist.is_gloo_available(), "CPU Gloo is required for this regression"
+    context = mp.spawn(_validate_worker, args=(str(tmp_path),), nprocs=2, join=False)
+    try:
+        deadline = time.monotonic() + 150
+        while not context.join(timeout=5):
+            assert time.monotonic() < deadline, "Validation collectives did not terminate"
+    finally:
+        for process in context.processes:
+            if process.is_alive():
+                process.terminate()
+            process.join(timeout=10)
+    reports = [json.loads((tmp_path / f"rank-{rank}.json").read_text()) for rank in (0, 1)]
+    assert reports[0] == reports[1]
+    for kind in ("torch", "ds_torch", "ds_engine"):
+        assert reports[0][f"{kind}-reject_best"] == {"rejected": True, "unchanged": True}
+        assert reports[0][f"{kind}-valid"]["acc"]["model.pt.ep1"] == pytest.approx(0.5)
+        assert reports[0][f"{kind}-valid"]["loss"]["model.pt.ep1"] == pytest.approx(3.0)
+        assert reports[0][f"{kind}-missing"]["acc"] == {}
+        assert reports[0][f"{kind}-missing"]["loss"]["model.pt.ep1"] == pytest.approx(3.0)
+        for case in ("nonfinite", "empty"):
+            assert reports[0][f"{kind}-{case}"] == {"acc": {}, "loss": {}}
diff --git a/tests/test_checkpoint_metric_presence.py b/tests/test_checkpoint_metric_presence.py
new file mode 100644
index 0000000000..07cce56ecb
--- /dev/null
+++ b/tests/test_checkpoint_metric_presence.py
@@ -0,0 +1,301 @@
+"""Exercise validation, checkpoint files and ranking without acoustic weights."""
+
+import logging
+from pathlib import Path
+
+import pytest
+import torch
+
+from funasr.train_utils.average_nbest_models import _get_checkpoint_paths, average_checkpoints
+from funasr.train_utils.trainer import Trainer as TrainerTorch
+from funasr.train_utils.trainer_ds import Trainer as TrainerDs
+
+
+SAVE_PATHS = ["torch", "ds_torch", "ds_engine"]
+
+
+class MetricModel(torch.nn.Module):
+    def __init__(self):
+        super().__init__()
+        self.marker = torch.nn.Parameter(torch.zeros(()))
+
+    def forward(self, value, accuracy="missing"):
+        stats = {"loss": value, "acc_rich": value.new_tensor(0.8)}
+        if accuracy != "missing":
+            stats["acc"] = None if accuracy is None else value.new_tensor(accuracy)
+        return value, stats, value.new_tensor(1.0)
+
+    def save_checkpoint(self, save_dir, tag, client_state):
+        # Model the engine's save boundary, not distributed DeepSpeed training.
+        path = Path(save_dir) / tag
+        path.mkdir(exist_ok=True)
+        torch.save({**client_state, "state_dict": self.state_dict()}, path / "mp_rank_00_model_states.pt")
+
+    def load_checkpoint(self, save_dir, tag):
+        path = Path(save_dir) / tag / "mp_rank_00_model_states.pt"
+        state = torch.load(path, weights_only=True)
+        self.load_state_dict(state["state_dict"])
+        return str(path), state
+
+
+class Batches:
+    def __init__(self, values):
+        self.values = values
+        self.batch_sampler = self
+
+    def set_epoch(self, epoch):
+        pass
+
+    def __len__(self):
+        return len(self.values)
+
+    def __iter__(self):
+        for loss, accuracy in self.values:
+            yield {"value": torch.tensor(loss), "accuracy": accuracy}
+
+
+class Run:
+    def __init__(self, path, kind, ranking="acc", keep=2):
+        self.path = path
+        self.kind = kind
+        kwargs = dict(output_dir=str(path), device="cpu", log_interval=100,
+                      avg_keep_nbest_models_type=ranking, keep_nbest_models=keep)
+        self.trainer = (TrainerTorch(local_rank=0, **kwargs) if kind == "torch" else
+                        TrainerDs(rank=0, local_rank=0, world_size=1, use_deepspeed=False, **kwargs))
+        self.model = MetricModel()
+        self.optim = torch.optim.SGD(self.model.parameters(), lr=0.01)
+        self.scheduler = torch.optim.lr_scheduler.StepLR(self.optim, step_size=1)
+
+    def validate(self, epoch, values):
+        if self.kind == "ds_engine":
+            self.trainer.use_deepspeed = False
+        self.trainer.validate_epoch(model=self.model, dataloader_val=Batches(values), epoch=epoch)
+
+    def save(self, epoch):
+        if self.kind == "ds_engine":
+            self.trainer.use_deepspeed = True
+        self.trainer.save_checkpoint(epoch=epoch, model=self.model,
+                                     optim=self.optim, scheduler=self.scheduler)
+
+    def checkpoint(self, name):
+        path = self.path / name
+        if self.kind == "ds_engine":
+            path = path / "mp_rank_00_model_states.pt"
+        return torch.load(path, weights_only=True)
+
+    def close(self):
+        writer = getattr(self.trainer, "writer", None)
+        if writer is not None:
+            writer.close()
+
+
+@pytest.fixture(params=SAVE_PATHS)
+def run(request, tmp_path):
+    case = Run(tmp_path, request.param)
+    yield case
+    case.close()
+
+
+@pytest.mark.parametrize("accuracy", ["missing", None, float("nan"), float("inf")])
+def test_unavailable_accuracy_never_ranks_or_averages(run, accuracy, caplog):
+    with caplog.at_level(logging.WARNING):
+        for epoch in (1, 2):
+            run.validate(epoch, [(1.0, accuracy)])
+            run.save(epoch)
+    assert run.trainer.val_acc_step_or_epoch == {}
+    assert run.trainer.saved_ckpts == {}
+    assert run.trainer.best_step_or_epoch == ""
+    assert not (run.path / "model.pt.best").exists()
+    assert run.checkpoint("model.pt")["val_acc_step_or_epoch"] == {}
+    assert _get_checkpoint_paths(str(run.path), use_deepspeed=run.kind == "ds_engine") == []
+    messages = [r.message for r in caplog.records if "avg_keep_nbest_models_type=loss" in r.message]
+    assert len(messages) == 1
+
+
+@pytest.mark.parametrize("values", [[(1.0, 0.4), (1.0, "missing")],
+                                    [(1.0, "missing"), (1.0, 0.4)]])
+def test_partial_accuracy_is_not_a_validation_score(run, values):
+    run.validate(1, values)
+    run.save(1)
+    assert run.trainer.val_acc_step_or_epoch == {}
+    assert run.trainer.val_loss_step_or_epoch == {"model.pt.ep1": 1.0}
+    assert run.trainer.saved_ckpts == {}
+
+
+def test_empty_validation_does_not_reuse_previous_averages(run):
+    run.validate(1, [(3.0, 0.5)])
+    run.save(1)
+    run.validate(2, [])
+    run.save(2)
+    assert "model.pt.ep2" not in run.trainer.val_acc_step_or_epoch
+    assert "model.pt.ep2" not in run.trainer.val_loss_step_or_epoch
+    assert run.trainer.best_step_or_epoch == "model.pt.ep1"
+
+
+@pytest.mark.parametrize("bad_loss", [float("nan"), float("inf")])
+def test_nonfinite_loss_does_not_publish_partial_metrics(run, bad_loss):
+    run.validate(1, [(1.0, 0.4), (bad_loss, 0.5)])
+    run.save(1)
+    assert run.trainer.val_loss_step_or_epoch == {}
+    assert run.trainer.val_acc_step_or_epoch == {}
+
+
+def test_real_zero_accuracy_preserves_existing_latest_tie(run):
+    for epoch in (1, 2, 3):
+        with torch.no_grad():
+            run.model.marker.fill_(epoch)
+        run.validate(epoch, [(1.0, 0.0)])
+        run.save(epoch)
+    assert run.trainer.best_step_or_epoch == "model.pt.ep3"
+    assert run.checkpoint("model.pt.best")["state_dict"]["marker"].item() == 3
+
+
+def test_validation_logs_current_running_means_not_previous_epoch(run, monkeypatch):
+    observed = []
+    monkeypatch.setattr(run.trainer, "log", lambda *a, **kw: observed.append(
+        (run.trainer.val_loss_avg, run.trainer.val_acc_avg)))
+    run.validate(1, [(1.0, 0.2), (3.0, 0.4)])
+    run.validate(2, [(5.0, 0.6)])
+    assert [v[0] for v in observed] == pytest.approx([1.0, 2.0, 5.0])
+    assert [v[1] for v in observed] == pytest.approx([0.2, 0.3, 0.6])
+
+
+def test_explicit_loss_best_pruning_and_average_agree(run, caplog):
+    run.trainer.avg_keep_nbest_models_type = "loss"
+    for epoch, loss in enumerate((3.0, 1.0, 2.0), 1):
+        with torch.no_grad():
+            run.model.marker.fill_(epoch)
+        run.validate(epoch, [(loss, "missing")])
+        run.save(epoch)
+    assert run.trainer.best_step_or_epoch == "model.pt.ep2"
+    assert run.checkpoint("model.pt.best")["state_dict"]["marker"].item() == 2
+    assert set(run.trainer.saved_ckpts) == {"model.pt.ep2", "model.pt.ep3"}
+    path = average_checkpoints(str(run.path), last_n=2, use_deepspeed=run.kind == "ds_engine")
+    assert torch.load(path, weights_only=True)["state_dict"]["marker"].item() == 2.5
+    assert not any("avg_keep_nbest_models_type=loss" in r.message for r in caplog.records)
+
+
+def test_revalidation_removes_stale_nonbest_metric_before_serialization(run):
+    run.validate(1, [(1.0, 0.9)])
+    run.save(1)
+    run.validate(2, [(1.0, 0.4)])
+    run.save(2)
+    run.validate(2, [(1.0, "missing")])
+    run.save(2)
+    state = run.checkpoint("model.pt")
+    assert "model.pt.ep2" not in state["val_acc_step_or_epoch"]
+    assert "model.pt.ep2" not in state["saved_ckpts"]
+    assert run.trainer.best_step_or_epoch == "model.pt.ep1"
+
+
+def test_invalid_revalidation_cannot_overwrite_current_best(run):
+    run.validate(1, [(1.0, 0.5)])
+    run.save(1)
+    before = run.checkpoint("model.pt.best")
+    with pytest.raises(ValueError, match="current best"):
+        run.validate(1, [(1.0, "missing")])
+    assert run.trainer.val_acc_step_or_epoch == {"model.pt.ep1": 0.5}
+    assert torch.equal(before["state_dict"]["marker"],
+                       run.checkpoint("model.pt.best")["state_dict"]["marker"])
+
+
+def test_resume_preserves_unavailable_metric_exclusion(run):
+    run.validate(1, [(1.0, "missing")])
+    run.save(1)
+    resumed = Run(run.path, run.kind)
+    try:
+        resumed.trainer.use_deepspeed = run.kind == "ds_engine" if run.kind != "torch" else False
+        resumed.trainer.resume_checkpoint(model=resumed.model, optim=resumed.optim, scheduler=resumed.scheduler)
+        assert resumed.trainer.val_acc_step_or_epoch == {}
+        assert resumed.trainer.saved_ckpts == {}
+    finally:
+        resumed.close()
+
+
+def test_resume_cannot_mix_accuracy_history_with_loss_ranking(run):
+    run.validate(1, [(1.0, 0.0)])
+    run.save(1)
+    resumed = Run(run.path, run.kind, ranking="loss")
+    try:
+        if run.kind != "torch":
+            resumed.trainer.use_deepspeed = run.kind == "ds_engine"
+        with pytest.raises(ValueError, match="ranking metric"):
+            resumed.trainer.resume_checkpoint(model=resumed.model, optim=resumed.optim, scheduler=resumed.scheduler)
+    finally:
+        resumed.close()
+
+
+def test_resume_retains_current_best_guard(run):
+    run.validate(1, [(1.0, 0.5)])
+    run.save(1)
+    resumed = Run(run.path, run.kind)
+    try:
+        if run.kind != "torch":
+            resumed.trainer.use_deepspeed = run.kind == "ds_engine"
+        resumed.trainer.resume_checkpoint(model=resumed.model, optim=resumed.optim, scheduler=resumed.scheduler)
+        assert resumed.trainer.best_step_or_epoch == "model.pt.ep1"
+        with pytest.raises(ValueError, match="current best"):
+            resumed.validate(1, [(1.0, "missing")])
+    finally:
+        resumed.close()
+
+
+@pytest.mark.parametrize("ranking,values", [("acc", [0.3, 0.9, 0.5]), ("loss", [3.0, 1.0, 2.0])])
+def test_persisted_ranking_matches_best_and_pruned_files(run, ranking, values):
+    run.trainer.avg_keep_nbest_models_type = ranking
+    run.trainer.keep_nbest_models = 1
+    for epoch, value in enumerate(values, 1):
+        loss, acc = (1.0, value) if ranking == "acc" else (value, "missing")
+        run.validate(epoch, [(loss, acc)])
+        run.save(epoch)
+        state = run.checkpoint("model.pt")
+        assert state["best_step_or_epoch"] == run.trainer.best_step_or_epoch
+        assert state["saved_ckpts"] == run.trainer.saved_ckpts
+        best = run.checkpoint("model.pt.best")
+        assert best["best_step_or_epoch"] == run.trainer.best_step_or_epoch
+        assert all((run.path / name).exists() for name in state["saved_ckpts"])
+    assert not (run.path / "model.pt.ep3").exists()
+    assert (run.path / "model.pt").exists()
+
+
+@pytest.mark.parametrize("failed_tag", ["model.pt", "model.pt.best"])
+def test_write_failure_does_not_delete_previous_candidate(run, failed_tag, monkeypatch):
+    run.trainer.keep_nbest_models = 1
+    with torch.no_grad():
+        run.model.marker.fill_(1)
+    run.validate(1, [(1.0, 0.3)])
+    run.save(1)
+    with torch.no_grad():
+        run.model.marker.fill_(2)
+    run.validate(2, [(1.0, 0.9)])
+    if run.kind == "ds_engine":
+        original = run.model.save_checkpoint
+
+        def fail_engine(save_dir, tag, client_state):
+            if tag == failed_tag:
+                raise OSError("simulated checkpoint write failure")
+            return original(save_dir, tag, client_state)
+
+        monkeypatch.setattr(run.model, "save_checkpoint", fail_engine)
+    else:
+        original = torch.save
+
+        def fail_torch(state, path, *args, **kwargs):
+            if Path(path).name == failed_tag:
+                raise OSError("simulated checkpoint write failure")
+            return original(state, path, *args, **kwargs)
+
+        monkeypatch.setattr(torch, "save", fail_torch)
+    with pytest.raises(OSError, match="simulated checkpoint"):
+        run.save(2)
+    assert (run.path / "model.pt.ep1").exists()
+    assert run.checkpoint("model.pt.best")["state_dict"]["marker"].item() == 1
+
+
+@pytest.mark.parametrize("ranking,scores", [("acc", {"model.pt.ep1": 0.9, "model.pt.ep2": 0.8, "model.pt.ep3": float("nan")}),
+                                          ("loss", {"model.pt.ep1": 0.1, "model.pt.ep2": 0.2, "model.pt.ep3": float("nan")})])
+def test_average_filters_nonfinite_and_missing_files_before_taking_n(tmp_path, ranking, scores):
+    torch.save({"avg_keep_nbest_models_type": ranking, f"val_{ranking}_step_or_epoch": scores}, tmp_path / "model.pt")
+    for epoch in (2, 3):
+        torch.save({"state_dict": {"x": torch.tensor(float(epoch))}}, tmp_path / f"model.pt.ep{epoch}")
+    assert _get_checkpoint_paths(str(tmp_path), last_n=1) == [str(tmp_path / "model.pt.ep2")]
diff --git a/tests/test_sensevoice_continual_finetuning_docs.py b/tests/test_sensevoice_continual_finetuning_docs.py
index 0c80dae3c1..299ce59107 100644
--- a/tests/test_sensevoice_continual_finetuning_docs.py
+++ b/tests/test_sensevoice_continual_finetuning_docs.py
@@ -38,6 +38,25 @@ def test_english_guide_covers_retention_controls_and_worked_example():
     assert all(item in guide for item in required)
 
 
+def test_checkpoint_selection_recipe_and_evaluation_boundaries():
+    recipe = (SENSEVOICE_DIR / "finetune.sh").read_text(encoding="utf-8")
+    assert "++train_conf.avg_keep_nbest_models_type=loss" in recipe
+    for name in ("CONTINUAL_FINETUNING.md", "CONTINUAL_FINETUNING_zh.md"):
+        guide = (SENSEVOICE_DIR / name).read_text(encoding="utf-8")
+        assert "++train_conf.avg_keep_nbest_models_type=loss" in guide
+        assert "acc_rich" in guide
+        assert "<|minnan|>" in guide
+        assert "93.3%" not in guide
+    english = (SENSEVOICE_DIR / "CONTINUAL_FINETUNING.md").read_text(encoding="utf-8")
+    chinese = (SENSEVOICE_DIR / "CONTINUAL_FINETUNING_zh.md").read_text(encoding="utf-8")
+    assert "independently audited" in english
+    assert "new output directory" in english
+    assert "allowlist" in english
+    assert "独立核验" in chinese
+    assert "新的输出目录" in chinese
+    assert "白名单" in chinese
+
+
 def test_chinese_guide_covers_retention_controls_and_worked_example():
     guide = (SENSEVOICE_DIR / "CONTINUAL_FINETUNING_zh.md").read_text(encoding="utf-8")