feat: P0 训练闭环核心功能实现

P0-1 模型路径治理:
- 新增 003_model_path_governance.sql 迁移，models 表增加 can_train 字段
- create_model/update_model 自动计算 can_train（非API+有路径=可训练）
- _compute_job_payload_from_task_node 拒绝 API 模型和无可训练路径模型
- 平台诊断规则增加 API 模型/路径缺失检测

P0-2 数据集格式校验:
- 新增 dataset_format.py，支持 Alpaca/ShareGPT/DPO/CPT 格式校验
- 训练预检时自动根据 train_type 匹配格式并校验内容字段
- llama_dataset_info 增加 DPO/CPT 格式列映射

P0-3 训练完成产物入库:
- _ensure_trained_model 使用 compute 节点返回的真实 artifacts
- 注册 per-file artifact 记录（含 size_bytes/checksum_sha256）
- trained_models 表增加 artifact_dir 字段

P0-4 失败日志拉取:
- poll_compute_jobs_once 检测到 failed/stopped 时强制拉取最后 200 行日志
- apply_compute_job 持久化失败日志片段到任务 payload

Co-Authored-By: Claude <noreply@anthropic.com>

backend/app/modules/data_process/dataset_format.py

@@ -0,0 +1,148 @@
+"""Dataset format validation for Alpaca, ShareGPT, DPO, CPT formats.
+
+Used by the training preflight flow to validate that uploaded dataset files
+conform to the declared format before submitting to the compute node.
+"""
+
+from __future__ import annotations
+
+import json
+from typing import Any
+
+
+def _load_sample(path: str | None, content: str | None = None, max_samples: int = 20) -> list[dict[str, Any]]:
+    """Load up to max_samples records from JSONL file path or raw content string."""
+    try:
+        if content is not None:
+            text = content.strip()
+        elif path:
+            with open(path, "r", encoding="utf-8") as fh:
+                text = fh.read().strip()
+        else:
+            return []
+    except Exception:
+        return []
+
+    if not text:
+        return []
+
+    lines = text.splitlines()[:max_samples]
+    records: list[dict[str, Any]] = []
+    for line in lines:
+        line = line.strip()
+        if not line:
+            continue
+        try:
+            record = json.loads(line)
+        except json.JSONDecodeError:
+            continue
+        if isinstance(record, dict):
+            records.append(record)
+    return records
+
+
+def _check_alpaca(records: list[dict[str, Any]]) -> list[str]:
+    """Validate Alpaca format: requires 'instruction' field."""
+    errors: list[str] = []
+    if not records:
+        errors.append("Alpaca 格式数据集无有效记录")
+        return errors
+    missing_instruction = sum(1 for r in records if not r.get("instruction"))
+    if missing_instruction:
+        errors.append(
+            f"Alpaca 格式要求每条记录包含 instruction 字段，"
+            f"前{len(records)}条中有{missing_instruction}条缺失"
+        )
+    return errors
+
+
+def _check_sharegpt(records: list[dict[str, Any]]) -> list[str]:
+    """Validate ShareGPT format: requires 'messages' (list of dicts with role/content)."""
+    errors: list[str] = []
+    if not records:
+        errors.append("ShareGPT 格式数据集无有效记录")
+        return errors
+    bad = 0
+    for r in records:
+        messages = r.get("messages")
+        if not isinstance(messages, list) or not messages:
+            bad += 1
+            continue
+        for msg in messages:
+            if not isinstance(msg, dict) or "role" not in msg or "content" not in msg:
+                bad += 1
+                break
+    if bad:
+        errors.append(
+            f"ShareGPT 格式要求每条记录包含 messages 列表，"
+            f"每条消息需有 role 和 content 字段，前{len(records)}条中有{bad}条不符合"
+        )
+    return errors
+
+
+def _check_dpo(records: list[dict[str, Any]]) -> list[str]:
+    """Validate DPO format: requires 'chosen' and 'rejected' fields."""
+    errors: list[str] = []
+    if not records:
+        errors.append("DPO 格式数据集无有效记录")
+        return errors
+    missing_chosen = sum(1 for r in records if not r.get("chosen"))
+    missing_rejected = sum(1 for r in records if not r.get("rejected"))
+    if missing_chosen:
+        errors.append(f"DPO 格式要求 chosen 字段，前{len(records)}条中有{missing_chosen}条缺失")
+    if missing_rejected:
+        errors.append(f"DPO 格式要求 rejected 字段，前{len(records)}条中有{missing_rejected}条缺失")
+    return errors
+
+
+def _check_cpt(records: list[dict[str, Any]]) -> list[str]:
+    """Validate CPT format: requires 'text' field, should NOT have instruction/output."""
+    errors: list[str] = []
+    if not records:
+        errors.append("CPT 格式数据集无有效记录")
+        return errors
+    missing_text = sum(1 for r in records if not r.get("text"))
+    has_instruction = sum(1 for r in records if r.get("instruction") or r.get("output"))
+    if missing_text:
+        errors.append(f"CPT 格式要求 text 字段，前{len(records)}条中有{missing_text}条缺失")
+    if has_instruction:
+        errors.append(
+            f"CPT 格式不应包含 instruction/output 字段（疑似 Alpaca 格式），"
+            f"前{len(records)}条中有{has_instruction}条包含此类字段"
+        )
+    return errors
+
+
+FORMAT_VALIDATORS = {
+    "alpaca": _check_alpaca,
+    "alpaca_jsonl": _check_alpaca,
+    "sharegpt": _check_sharegpt,
+    "dpo": _check_dpo,
+    "cpt": _check_cpt,
+    "pt": _check_cpt,
+}
+
+
+def validate_dataset_format(
+    dataset_format: str,
+    content: str | None = None,
+    path: str | None = None,
+    max_samples: int = 20,
+) -> list[str]:
+    """Validate dataset content against expected format.
+
+    Args:
+        dataset_format: One of 'alpaca', 'sharegpt', 'dpo', 'cpt'.
+        content: Raw file content (JSONL text). Mutually exclusive with path.
+        path: File path to read content from.
+        max_samples: Maximum records to sample for validation.
+
+    Returns:
+        List of error messages (empty if valid).
+    """
+    fmt = str(dataset_format).lower().strip()
+    validator = FORMAT_VALIDATORS.get(fmt)
+    if not validator:
+        return [f"不支持的数据集格式: {dataset_format}，支持的格式: {', '.join(sorted(FORMAT_VALIDATORS))}"]
+    records = _load_sample(path=path, content=content, max_samples=max_samples)
+    return validator(records)