scripts/synthesize_think_bon.py

#!/usr/bin/env python3
"""Synthesize <think> traces for SFT singleturn trajectories with BoN + judge.

This script is intentionally environment-agnostic. It assumes a JSON list of rows
with the common RAGEN SFT shape:

  {"messages": [{"role": "system"}, {"role": "user"}, {"role": "assistant"}, ...],
   "meta": {"source_id": ..., "turns": ..., "total_turns": ...}}

For each source_id, the complete trajectory row is selected, one reasoning trace
is synthesized per turn, and the selected traces are written back to every
cumulative singleturn prefix while keeping every original <answer>...</answer>
block exactly unchanged.


python3 /mnt/general/wanghy/RAGEN/scripts/synthesize_think_bon.py \
  --input /mnt/general/wanghy/RAGEN/runs/Sudoku__ppo_sudoku_actionmask__4x4/sft/step_999424_sft_singleturn_nohint.json \
  --output-dir /mnt/general/wanghy/RAGEN/runs/Sudoku__ppo_sudoku_actionmask__4x4/sft/ \
  --output-prefix step_999424_sft_singleturn_withthink \
  --versions sa,sas \
  --model /mnt/general/share/model/Qwen/Qwen2.5-7B-Instruct \
  --tensor-parallel-size 4 \
  --n 8 \
  --batch-size 32 \
  --judge-batch-size 32 \
  --limit-sources 50
"""

from __future__ import annotations

import argparse
import copy
import json
import re
from dataclasses import dataclass
from pathlib import Path
from typing import Any, Dict, Iterable, List, Optional, Sequence, Tuple


ANSWER_RE = re.compile(r"<answer>.*?</answer>", re.IGNORECASE | re.DOTALL)
THINK_RE = re.compile(r"<think>(.*?)</think>", re.IGNORECASE | re.DOTALL)
JSON_OBJ_RE = re.compile(r"\{.*\}", re.DOTALL)


@dataclass
class TurnExample:
    source_id: Any
    turn_idx: int
    total_turns: int
    user_content: str
    assistant_content: str
    answer_block: str
    next_user_content: Optional[str]


@dataclass
class FullTrajectory:
    source_id: Any
    sys_prefix: List[Dict[str, Any]]
    pairs: List[Tuple[Dict[str, Any], Dict[str, Any]]]
    meta: Dict[str, Any]


def parse_args() -> argparse.Namespace:
    parser = argparse.ArgumentParser(
        description="Synthesize expert-action thinking traces with per-turn BoN and LLM judge."
    )
    parser.add_argument("--input", "-i", type=Path, required=True, help="Input SFT JSON list.")
    parser.add_argument(
        "--output-dir",
        type=Path,
        default=None,
        help="Directory for output files. Defaults to input parent.",
    )
    parser.add_argument(
        "--output-prefix",
        default=None,
        help="Output filename prefix. Defaults to input stem.",
    )
    parser.add_argument(
        "--versions",
        default="sa,sas",
        help="Comma-separated versions: sa and/or sas. sa uses s,a; sas uses s,a,s'.",
    )
    parser.add_argument("--model", default=None, help="HF model path for tokenizer + vLLM.")
    parser.add_argument("--judge-model", default=None, help="Optional separate judge model path.")
    parser.add_argument("--n", type=int, default=8, help="BoN candidates per turn.")
    parser.add_argument(
        "--mode",
        default="per_turn",
        choices=["per_turn"],
        help="BoN mode. Currently only independent per-turn BoN is implemented.",
    )
    parser.add_argument("--limit-sources", type=int, default=None, help="Pilot limit by source_id count.")
    parser.add_argument("--source-ids", default="", help="Optional comma-separated source_id allowlist.")
    parser.add_argument("--batch-size", type=int, default=64, help="Prompt batch size for generation.")
    parser.add_argument("--judge-batch-size", type=int, default=64, help="Prompt batch size for judge.")
    parser.add_argument("--temperature", type=float, default=0.7)
    parser.add_argument("--top-p", type=float, default=0.95)
    parser.add_argument("--top-k", type=int, default=-1)
    parser.add_argument("--max-tokens", type=int, default=160, help="Max tokens for think generation.")
    parser.add_argument("--judge-temperature", type=float, default=0.0)
    parser.add_argument("--judge-max-tokens", type=int, default=768)
    parser.add_argument("--tensor-parallel-size", type=int, default=1)
    parser.add_argument("--judge-tensor-parallel-size", type=int, default=None)
    parser.add_argument("--dtype", default="auto")
    parser.add_argument("--gpu-memory-utilization", type=float, default=0.9)
    parser.add_argument("--max-model-len", type=int, default=None)
    parser.add_argument("--trust-remote-code", action="store_true")
    parser.add_argument("--min-judge-score", type=float, default=3.0)
    parser.add_argument("--save-candidates", action="store_true", help="Store all candidates in report.")
    parser.add_argument(
        "--selected-only",
        action="store_true",
        help="Write only rows whose source_id was selected by --limit-sources/--source-ids.",
    )
    parser.add_argument("--no-cache", action="store_true", help="Disable JSONL cache/resume.")
    parser.add_argument("--dry-run", action="store_true", help="Do not load vLLM; create deterministic mock thinks.")
    parser.add_argument("--indent", type=int, default=2, help="JSON output indent. Use -1 for compact.")
    return parser.parse_args()


def load_json_list(path: Path) -> List[Dict[str, Any]]:
    with path.open("r", encoding="utf-8") as f:
        data = json.load(f)
    if not isinstance(data, list):
        raise ValueError(f"Expected JSON list at {path}, got {type(data).__name__}")
    if not all(isinstance(row, dict) for row in data):
        raise ValueError(f"Expected all rows to be objects in {path}")
    return data


def dump_json(path: Path, data: Any, indent: int) -> None:
    path.parent.mkdir(parents=True, exist_ok=True)
    kwargs = {"ensure_ascii": False}
    if indent >= 0:
        kwargs["indent"] = indent
    with path.open("w", encoding="utf-8") as f:
        json.dump(data, f, **kwargs)


def extract_system_prefix(messages: Sequence[Dict[str, Any]]) -> List[Dict[str, Any]]:
    out: List[Dict[str, Any]] = []
    for msg in messages:
        if msg.get("role") == "system":
            out.append(copy.deepcopy(msg))
        else:
            break
    return out


def collect_pairs(messages: Sequence[Dict[str, Any]], start_idx: int = 0) -> List[Tuple[Dict[str, Any], Dict[str, Any]]]:
    pairs: List[Tuple[Dict[str, Any], Dict[str, Any]]] = []
    idx = start_idx
    while idx < len(messages):
        while idx < len(messages) and messages[idx].get("role") != "user":
            idx += 1
        if idx >= len(messages):
            break
        if idx + 1 < len(messages) and messages[idx + 1].get("role") == "assistant":
            pairs.append((copy.deepcopy(messages[idx]), copy.deepcopy(messages[idx + 1])))
            idx += 2
        else:
            idx += 1
    return pairs


def to_int(value: Any, default: int = 0) -> int:
    try:
        return int(value)
    except (TypeError, ValueError):
        return default


def source_key(source_id: Any) -> str:
    return str(source_id)


def group_rows(rows: Sequence[Dict[str, Any]]) -> Dict[Any, List[Dict[str, Any]]]:
    groups: Dict[Any, List[Dict[str, Any]]] = {}
    for idx, row in enumerate(rows):
        meta = row.get("meta") or {}
        source_id = meta.get("source_id", f"missing_source_{idx}")
        groups.setdefault(source_id, []).append(row)
    for items in groups.values():
        items.sort(key=lambda r: to_int((r.get("meta") or {}).get("turns"), 0))
    return groups


def select_full_row(source_id: Any, items: Sequence[Dict[str, Any]]) -> Dict[str, Any]:
    exact = [
        row
        for row in items
        if to_int((row.get("meta") or {}).get("turns"), -1)
        == to_int((row.get("meta") or {}).get("total_turns"), -2)
    ]
    if exact:
        return exact[-1]
    return max(items, key=lambda r: to_int((r.get("meta") or {}).get("turns"), 0))


def build_full_trajectories(rows: Sequence[Dict[str, Any]]) -> Dict[Any, FullTrajectory]:
    groups = group_rows(rows)
    full: Dict[Any, FullTrajectory] = {}
    for source_id, items in groups.items():
        row = select_full_row(source_id, items)
        messages = row.get("messages") or []
        if not isinstance(messages, list):
            continue
        sys_prefix = extract_system_prefix(messages)
        pairs = collect_pairs(messages, start_idx=len(sys_prefix))
        if not pairs:
            continue
        full[source_id] = FullTrajectory(
            source_id=source_id,
            sys_prefix=sys_prefix,
            pairs=pairs,
            meta=dict(row.get("meta") or {}),
        )
    return full


def extract_answer_block(text: str) -> str:
    match = ANSWER_RE.search(text or "")
    return match.group(0) if match is not None else ""


def clean_think(text: str) -> str:
    text = (text or "").strip()
    think_match = THINK_RE.search(text)
    if think_match is not None:
        text = think_match.group(1).strip()
    text = re.split(r"<\s*/?\s*answer\s*>", text, flags=re.IGNORECASE)[0]
    text = re.sub(r"</?think>", "", text, flags=re.IGNORECASE)
    text = re.sub(r"\s+", " ", text).strip()
    text = text.strip('` \t\n\r"')
    return text


def make_response(think: str, answer_block: str) -> str:
    return f"<think>{think.strip()}</think>{answer_block}"


def iter_turns(full: Dict[Any, FullTrajectory]) -> List[TurnExample]:
    turns: List[TurnExample] = []
    for source_id, traj in full.items():
        total_turns = len(traj.pairs)
        for i, (user_msg, asst_msg) in enumerate(traj.pairs):
            answer_block = extract_answer_block(str(asst_msg.get("content", "")))
            next_user = None
            if i + 1 < total_turns:
                next_user = str(traj.pairs[i + 1][0].get("content", ""))
            turns.append(
                TurnExample(
                    source_id=source_id,
                    turn_idx=i + 1,
                    total_turns=total_turns,
                    user_content=str(user_msg.get("content", "")),
                    assistant_content=str(asst_msg.get("content", "")),
                    answer_block=answer_block,
                    next_user_content=next_user,
                )
            )
    return turns


def build_generation_messages(example: TurnExample, version: str) -> List[Dict[str, str]]:
    if version not in {"sa", "sas"}:
        raise ValueError(f"Unknown version: {version}")
    sas_available = version == "sas" and example.next_user_content is not None
    parts = [
        "We are creating high-quality SFT reasoning for an expert trajectory.",
        "The expert action is fixed. Your job is only to write the inner text for <think>...</think>.",
        "Do not output <think>, </think>, <answer>, JSON, bullets, or any extra wrapper.",
        "Do not change or restate a different action. Do not invent hidden facts, future rewards, or unsupported optimality claims.",
        "Keep it concise: 1-3 English sentences explaining why the fixed action is reasonable from the visible context.",
        "",
        "Current observation/state s:",
        "```text",
        example.user_content.strip(),
        "```",
        "",
        "Fixed expert action a:",
        "```text",
        example.answer_block.strip() or example.assistant_content.strip(),
        "```",
    ]
    if sas_available:
        parts.extend(
            [
                "",
                "Observed next state/feedback s' after executing the fixed action:",
                "```text",
                str(example.next_user_content).strip(),
                "```",
                "Use s' only to ground the explanation of the observed transition; never alter the fixed action.",
            ]
        )
    elif version == "sas":
        parts.extend(
            [
                "",
                "No next state s' is available for this final turn, so explain using only s and a.",
            ]
        )
    return [
        {
            "role": "system",
            "content": "You write faithful, concise reasoning for fixed expert actions.",
        },
        {"role": "user", "content": "\n".join(parts)},
    ]


def build_judge_messages(example: TurnExample, version: str, candidates: Sequence[str]) -> List[Dict[str, str]]:
    candidate_text = "\n".join(f"[{i + 1}] {cand}" for i, cand in enumerate(candidates))
    sas_available = version == "sas" and example.next_user_content is not None
    parts = [
        "You are auditing candidate <think> texts for an expert SFT trajectory.",
        "The expert action is fixed. Select the candidate that best explains it while staying faithful to the visible context.",
        "Penalize unsupported factual claims, contradicted claims, changing the action, excessive certainty such as 'only'/'optimal' without clear support, verbosity, and format pollution.",
        "Return strict JSON only, with no markdown.",
        "",
        "Current observation/state s:",
        "```text",
        example.user_content.strip(),
        "```",
        "",
        "Fixed expert action a:",
        "```text",
        example.answer_block.strip() or example.assistant_content.strip(),
        "```",
    ]
    if sas_available:
        parts.extend(
            [
                "",
                "Observed next state/feedback s' after executing a:",
                "```text",
                str(example.next_user_content).strip(),
                "```",
            ]
        )
    elif version == "sas":
        parts.append("\nNo next state s' is available for this final turn.")
    parts.extend(
        [
            "",
            "Candidates:",
            candidate_text,
            "",
            "Use this JSON schema:",
            '{"best_index": 1, "scores": [{"index": 1, "score": 1, "unsupported_claims": 0, "contradictions": 0, "reason": "short reason"}], "selected_reason": "short reason", "low_quality": false}',
            "Scores are from 1 to 5. Set low_quality=true if the best candidate is still weak or generic.",
        ]
    )
    return [
        {"role": "system", "content": "You are a strict factuality judge for reasoning traces."},
        {"role": "user", "content": "\n".join(parts)},
    ]


def render_prompt(tokenizer: Any, messages: List[Dict[str, str]]) -> str:
    return tokenizer.apply_chat_template(messages, add_generation_prompt=True, tokenize=False)


def load_vllm_model(
    model_path: str,
    args: argparse.Namespace,
    tensor_parallel_size: Optional[int] = None,
) -> Tuple[Any, Any]:
    try:
        from transformers import AutoTokenizer
        from vllm import LLM
    except ImportError as exc:
        raise RuntimeError("This script requires `vllm` and `transformers`.") from exc

    tokenizer = AutoTokenizer.from_pretrained(model_path, trust_remote_code=bool(args.trust_remote_code))
    llm_kwargs: Dict[str, Any] = {
        "model": model_path,
        "tensor_parallel_size": int(tensor_parallel_size or args.tensor_parallel_size),
        "dtype": args.dtype,
        "gpu_memory_utilization": float(args.gpu_memory_utilization),
        "trust_remote_code": bool(args.trust_remote_code),
    }
    if args.max_model_len is not None:
        llm_kwargs["max_model_len"] = int(args.max_model_len)
    return LLM(**llm_kwargs), tokenizer


def make_sampling_params(args: argparse.Namespace, *, judge: bool = False) -> Any:
    try:
        from vllm import SamplingParams
    except ImportError as exc:
        raise RuntimeError("This script requires `vllm`.") from exc
    if judge:
        return SamplingParams(
            temperature=float(args.judge_temperature),
            top_p=1.0,
            max_tokens=int(args.judge_max_tokens),
        )
    return SamplingParams(
        n=int(args.n),
        temperature=float(args.temperature),
        top_p=float(args.top_p),
        top_k=int(args.top_k),
        max_tokens=int(args.max_tokens),
    )


def chunks(items: Sequence[Any], size: int) -> Iterable[Sequence[Any]]:
    if size <= 0:
        yield items
        return
    for start in range(0, len(items), size):
        yield items[start : start + size]


def parse_judge_json(text: str) -> Dict[str, Any]:
    text = (text or "").strip()
    match = JSON_OBJ_RE.search(text)
    if match is not None:
        text = match.group(0)
    try:
        obj = json.loads(text)
        if isinstance(obj, dict):
            return obj
    except json.JSONDecodeError:
        pass
    return {}


def selected_score(judge_obj: Dict[str, Any], best_index: int) -> float:
    for item in judge_obj.get("scores") or []:
        if isinstance(item, dict) and to_int(item.get("index"), -1) == best_index:
            try:
                return float(item.get("score", 0.0))
            except (TypeError, ValueError):
                return 0.0
    return 0.0


def fallback_think(version: str) -> str:
    if version == "sas":
        return (
            "The expert action is kept fixed and is explained using the current observation "
            "together with the observed next-state feedback, without changing the action."
        )
    return (
        "The expert action is kept fixed and is chosen based on the current observation "
        "and task constraints, aiming to make progress without changing the demonstrated action."
    )


def cache_key(version: str, source_id: Any, turn_idx: int) -> str:
    return json.dumps(
        {"version": version, "source_id": source_id, "turn_idx": turn_idx},
        ensure_ascii=False,
        sort_keys=True,
    )


def load_cache(path: Path) -> Dict[str, Dict[str, Any]]:
    cache: Dict[str, Dict[str, Any]] = {}
    if not path.exists():
        return cache
    with path.open("r", encoding="utf-8") as f:
        for line_no, line in enumerate(f, start=1):
            line = line.strip()
            if not line:
                continue
            try:
                row = json.loads(line)
            except json.JSONDecodeError:
                print(f"Warning: skipped invalid cache line {path}:{line_no}")
                continue
            key = row.get("cache_key")
            if isinstance(key, str):
                cache[key] = row
    return cache


def append_cache(path: Path, rows: Sequence[Dict[str, Any]]) -> None:
    if not rows:
        return
    path.parent.mkdir(parents=True, exist_ok=True)
    with path.open("a", encoding="utf-8") as f:
        for row in rows:
            f.write(json.dumps(row, ensure_ascii=False) + "\n")


def dry_candidates(example: TurnExample, version: str, n: int) -> List[str]:
    base = "This fixed expert action is explained from the visible state while preserving the demonstrated answer."
    if version == "sas" and example.next_user_content is not None:
        base = "This fixed expert action is explained from the visible state and the observed next-state feedback."
    return [f"{base} Candidate {i + 1}." for i in range(n)]


def synthesize_version(
    *,
    version: str,
    turns: Sequence[TurnExample],
    args: argparse.Namespace,
    output_dir: Path,
    output_prefix: str,
    llm: Any,
    tokenizer: Any,
    judge_llm: Any,
    judge_tokenizer: Any,
) -> Dict[Tuple[Any, int], Dict[str, Any]]:
    cache_path = output_dir / f"{output_prefix}_with_think_{version}_bon{args.n}.cache.jsonl"
    cache = {} if args.no_cache else load_cache(cache_path)
    results: Dict[Tuple[Any, int], Dict[str, Any]] = {}
    missing: List[TurnExample] = []
    for ex in turns:
        key = cache_key(version, ex.source_id, ex.turn_idx)
        cached = cache.get(key)
        if cached is not None and cached.get("selected_think"):
            results[(ex.source_id, ex.turn_idx)] = cached
        else:
            missing.append(ex)

    print(f"[{version}] turns={len(turns)} cached={len(results)} missing={len(missing)}")
    gen_params = None if args.dry_run else make_sampling_params(args, judge=False)
    judge_params = None if args.dry_run else make_sampling_params(args, judge=True)

    for batch_no, batch in enumerate(chunks(missing, int(args.batch_size)), start=1):
        batch = list(batch)
        if args.dry_run:
            all_candidates = [dry_candidates(ex, version, int(args.n)) for ex in batch]
        else:
            prompts = [render_prompt(tokenizer, build_generation_messages(ex, version)) for ex in batch]
            outputs = llm.generate(prompts, sampling_params=gen_params)
            all_candidates = []
            for out in outputs:
                candidates = [clean_think(candidate.text) for candidate in out.outputs]
                candidates = [cand for cand in candidates if cand]
                all_candidates.append(candidates)

        judge_inputs: List[Tuple[TurnExample, List[str]]] = []
        batch_rows: List[Dict[str, Any]] = []
        for ex, candidates in zip(batch, all_candidates):
            if not candidates:
                selected = fallback_think(version)
                row = {
                    "cache_key": cache_key(version, ex.source_id, ex.turn_idx),
                    "version": version,
                    "source_id": ex.source_id,
                    "turn_idx": ex.turn_idx,
                    "total_turns": ex.total_turns,
                    "selected_think": selected,
                    "selected_index": None,
                    "score": 0.0,
                    "low_quality": True,
                    "fallback": True,
                    "missing_next_state": version == "sas" and ex.next_user_content is None,
                    "selected_reason": "No valid generation candidates; used fallback.",
                }
                if args.save_candidates:
                    row["candidates"] = []
                batch_rows.append(row)
            else:
                judge_inputs.append((ex, candidates))

        judge_texts: List[str] = []
        if judge_inputs:
            if args.dry_run:
                judge_texts = [
                    json.dumps(
                        {
                            "best_index": 1,
                            "scores": [
                                {
                                    "index": 1,
                                    "score": 3,
                                    "unsupported_claims": 0,
                                    "contradictions": 0,
                                    "reason": "dry run",
                                }
                            ],
                            "selected_reason": "dry run",
                            "low_quality": False,
                        }
                    )
                    for _ in judge_inputs
                ]
            else:
                judge_prompts = [
                    render_prompt(judge_tokenizer, build_judge_messages(ex, version, candidates))
                    for ex, candidates in judge_inputs
                ]
                judge_texts = []
                for judge_chunk in chunks(judge_prompts, int(args.judge_batch_size)):
                    judge_outputs = judge_llm.generate(list(judge_chunk), sampling_params=judge_params)
                    judge_texts.extend(out.outputs[0].text for out in judge_outputs)

        for (ex, candidates), judge_text in zip(judge_inputs, judge_texts):
            judge_obj = parse_judge_json(judge_text)
            best_index = to_int(judge_obj.get("best_index"), 1)
            if best_index < 1 or best_index > len(candidates):
                best_index = 1
            selected = candidates[best_index - 1]
            score = selected_score(judge_obj, best_index)
            if score <= 0.0:
                score = 3.0 if selected else 0.0
            low_quality = bool(judge_obj.get("low_quality", False)) or score < float(args.min_judge_score)
            row = {
                "cache_key": cache_key(version, ex.source_id, ex.turn_idx),
                "version": version,
                "source_id": ex.source_id,
                "turn_idx": ex.turn_idx,
                "total_turns": ex.total_turns,
                "selected_think": selected or fallback_think(version),
                "selected_index": best_index,
                "score": score,
                "low_quality": low_quality,
                "fallback": not bool(selected),
                "missing_next_state": version == "sas" and ex.next_user_content is None,
                "selected_reason": str(judge_obj.get("selected_reason", "")),
            }
            if args.save_candidates:
                row["candidates"] = candidates
                row["judge"] = judge_obj
                row["judge_raw"] = judge_text
            batch_rows.append(row)

        append_cache(cache_path, batch_rows) if not args.no_cache else None
        for row in batch_rows:
            results[(row["source_id"], int(row["turn_idx"]))] = row
        print(f"[{version}] batch {batch_no}: wrote {len(batch_rows)} turn results")
    return results


def rebuild_rows(
    rows: Sequence[Dict[str, Any]],
    full: Dict[Any, FullTrajectory],
    result_map: Dict[Tuple[Any, int], Dict[str, Any]],
) -> List[Dict[str, Any]]:
    rebuilt_by_source: Dict[Any, List[Tuple[Dict[str, Any], Dict[str, Any]]]] = {}
    for source_id, traj in full.items():
        new_pairs: List[Tuple[Dict[str, Any], Dict[str, Any]]] = []
        for idx, (user_msg, asst_msg) in enumerate(traj.pairs, start=1):
            answer_block = extract_answer_block(str(asst_msg.get("content", "")))
            result = result_map.get((source_id, idx))
            think = str(result.get("selected_think", "")) if result else fallback_think("sa")
            new_user = copy.deepcopy(user_msg)
            new_asst = copy.deepcopy(asst_msg)
            if answer_block:
                new_asst["content"] = make_response(think, answer_block)
            else:
                new_asst["content"] = str(asst_msg.get("content", ""))
            new_pairs.append((new_user, new_asst))
        rebuilt_by_source[source_id] = new_pairs

    output: List[Dict[str, Any]] = []
    for idx, row in enumerate(rows):
        meta = row.get("meta") or {}
        source_id = meta.get("source_id", f"missing_source_{idx}")
        turns = to_int(meta.get("turns"), 0)
        new_row = copy.deepcopy(row)
        traj = full.get(source_id)
        pairs = rebuilt_by_source.get(source_id)
        if traj is None or pairs is None or turns <= 0:
            output.append(new_row)
            continue
        turns = min(turns, len(pairs))
        new_row["messages"] = copy.deepcopy(traj.sys_prefix) + [
            copy.deepcopy(msg) for pair in pairs[:turns] for msg in pair
        ]
        output.append(new_row)
    return output


def validate_answer_unchanged(original: Sequence[Dict[str, Any]], rebuilt: Sequence[Dict[str, Any]]) -> Dict[str, Any]:
    if len(original) != len(rebuilt):
        raise ValueError(f"Row count changed: original={len(original)} rebuilt={len(rebuilt)}")
    checked = 0
    mismatches: List[Dict[str, Any]] = []
    for row_idx, (old_row, new_row) in enumerate(zip(original, rebuilt)):
        old_pairs = collect_pairs(old_row.get("messages") or [], start_idx=len(extract_system_prefix(old_row.get("messages") or [])))
        new_pairs = collect_pairs(new_row.get("messages") or [], start_idx=len(extract_system_prefix(new_row.get("messages") or [])))
        if len(old_pairs) != len(new_pairs):
            mismatches.append({"row_idx": row_idx, "reason": "pair_count_changed"})
            continue
        for turn_idx, ((_, old_asst), (_, new_asst)) in enumerate(zip(old_pairs, new_pairs), start=1):
            old_answer = extract_answer_block(str(old_asst.get("content", "")))
            new_answer = extract_answer_block(str(new_asst.get("content", "")))
            checked += 1
            if old_answer != new_answer:
                mismatches.append(
                    {
                        "row_idx": row_idx,
                        "turn_idx": turn_idx,
                        "old_answer": old_answer,
                        "new_answer": new_answer,
                    }
                )
                if len(mismatches) >= 20:
                    break
        if len(mismatches) >= 20:
            break
    if mismatches:
        raise ValueError(f"Answer validation failed, examples: {mismatches[:3]}")
    return {"checked_assistant_messages": checked, "answer_mismatches": 0}


def filter_full_by_args(full: Dict[Any, FullTrajectory], args: argparse.Namespace) -> Dict[Any, FullTrajectory]:
    selected = dict(full)
    if args.source_ids.strip():
        allow = {item.strip() for item in args.source_ids.split(",") if item.strip()}
        selected = {sid: traj for sid, traj in selected.items() if source_key(sid) in allow}
    if args.limit_sources is not None:
        limited: Dict[Any, FullTrajectory] = {}
        for sid in list(selected.keys())[: int(args.limit_sources)]:
            limited[sid] = selected[sid]
        selected = limited
    return selected


def report_from_results(
    *,
    version: str,
    result_map: Dict[Tuple[Any, int], Dict[str, Any]],
    validation: Dict[str, Any],
    args: argparse.Namespace,
) -> Dict[str, Any]:
    values = list(result_map.values())
    low_quality = sum(1 for row in values if row.get("low_quality"))
    fallback = sum(1 for row in values if row.get("fallback"))
    missing_next = sum(1 for row in values if row.get("missing_next_state"))
    scores = [float(row.get("score", 0.0)) for row in values]
    summary = {
        "version": version,
        "n": int(args.n),
        "turn_results": len(values),
        "low_quality": low_quality,
        "fallback": fallback,
        "missing_next_state": missing_next,
        "avg_score": sum(scores) / len(scores) if scores else 0.0,
        "min_score": min(scores) if scores else 0.0,
        "max_score": max(scores) if scores else 0.0,
        **validation,
    }
    per_turn: List[Dict[str, Any]] = []
    for row in values:
        item = {
            "source_id": row.get("source_id"),
            "turn_idx": row.get("turn_idx"),
            "total_turns": row.get("total_turns"),
            "selected_index": row.get("selected_index"),
            "score": row.get("score"),
            "low_quality": row.get("low_quality"),
            "fallback": row.get("fallback"),
            "missing_next_state": row.get("missing_next_state"),
            "selected_reason": row.get("selected_reason", ""),
        }
        if args.save_candidates:
            item["selected_think"] = row.get("selected_think")
            item["candidates"] = row.get("candidates", [])
            item["judge"] = row.get("judge", {})
        per_turn.append(item)
    return {"summary": summary, "per_turn": per_turn}


def main() -> None:
    args = parse_args()
    versions = [v.strip() for v in args.versions.split(",") if v.strip()]
    if not versions or any(v not in {"sa", "sas"} for v in versions):
        raise ValueError("--versions must contain only sa and/or sas")
    if not args.dry_run and not args.model:
        raise ValueError("--model is required unless --dry-run is set")

    input_path = args.input.expanduser().resolve()
    output_dir = (args.output_dir or input_path.parent).expanduser().resolve()
    output_prefix = args.output_prefix or input_path.stem

    print(f"Loading input: {input_path}")
    rows = load_json_list(input_path)
    full_all = build_full_trajectories(rows)
    full_selected = filter_full_by_args(full_all, args)
    if not full_selected:
        raise ValueError("No usable trajectories selected.")
    turns = iter_turns(full_selected)
    print(f"Rows={len(rows)} sources={len(full_all)} selected_sources={len(full_selected)} selected_turns={len(turns)}")

    llm = tokenizer = judge_llm = judge_tokenizer = None
    if not args.dry_run:
        llm, tokenizer = load_vllm_model(args.model, args, tensor_parallel_size=args.tensor_parallel_size)
        judge_model = args.judge_model or args.model
        if judge_model == args.model:
            judge_llm, judge_tokenizer = llm, tokenizer
        else:
            judge_tp = args.judge_tensor_parallel_size or args.tensor_parallel_size
            judge_llm, judge_tokenizer = load_vllm_model(judge_model, args, tensor_parallel_size=judge_tp)

    for version in versions:
        result_map = synthesize_version(
            version=version,
            turns=turns,
            args=args,
            output_dir=output_dir,
            output_prefix=output_prefix,
            llm=llm,
            tokenizer=tokenizer,
            judge_llm=judge_llm,
            judge_tokenizer=judge_tokenizer,
        )
        rows_for_output = [
            row
            for idx, row in enumerate(rows)
            if not args.selected_only
            or (row.get("meta") or {}).get("source_id", f"missing_source_{idx}") in full_selected
        ]
        rebuilt = rebuild_rows(rows_for_output, full_selected, result_map)
        validation = validate_answer_unchanged(rows_for_output, rebuilt)
        out_path = output_dir / f"{output_prefix}_with_think_{version}_bon{args.n}.json"
        report_path = output_dir / f"{output_prefix}_with_think_{version}_bon{args.n}.report.json"
        dump_json(out_path, rebuilt, indent=int(args.indent))
        report = report_from_results(version=version, result_map=result_map, validation=validation, args=args)
        dump_json(report_path, report, indent=2)
        print(f"[{version}] wrote SFT: {out_path}")
        print(f"[{version}] wrote report: {report_path}")
        print(f"[{version}] summary: {json.dumps(report['summary'], ensure_ascii=False)}")


if __name__ == "__main__":
    main()