feat(v2): T10 轨迹回放与会议结果复盘——只读轨迹、unmatched 单列、更正追加

覆盖 AC-22/32/33（BR-13/21/31/32、E-05/23/26）。

后端：
- contracts/trajectory.py：TrajectoryStep 与 ReviewOutcome。
  TrajectoryStep 失败必有错误码、成本未知时币种留空、observable() 给出
  可读字段白名单（机器可读地排除任何推理过程字段）；
  ReviewOutcome 只在 matched 且有明确映射口径时才有二元标签，附条件/撤回/
  未送审一律留空，unmatched 不得挂快照。
- services/trajectory.py：
  · project_steps 把既有 run 的步骤投影成轨迹（顺序即 sequence，部分完成
    如实标注，失败保留，成本缺省留空不填 0）；
  · replay 只读回放并按 sequence 稳定分页，不存在或跨项目抛 KeyError；
  · record 追加会议结果：未知快照记 unmatched，更正要指向本项目既有记录，
    链必须能终止；denominator 只数 matched 且有通过/否决口径的记录。
- api/prescreen.py：新增轨迹回放、会议结果列表与追加三个端点。

未做：轨迹写入仍由既有 DurableWorker.save_step 负责（本批不重做运行执行），
因此目前没有 judgment/rule 类步骤的产出方；会议标签映射（E-26）仍属 T11。

验证：backend 全量 unittest 494 项 OK（T09 时 469 项，无回归）。

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

backend/contracts/trajectory.py

@@ -0,0 +1,112 @@
+"""T10 轨迹与会议结果契约。
+
+Owner：本文件（docs/v2/03-detailed-design.md §9.1 的 TrajectoryStep / ReviewOutcome）。
+`contracts/prescreen.py` 头部已明确把这两个对象排除在该文件之外，这里补上。
+
+两条不可让渡的规则：
+1. **只记录可观察动作**：步骤只保存计划、组件版本、输入输出引用、理由摘要与
+   错误码；**不存在**隐藏思维链字段，也不采集模型内部推理（BR-31 / AC-32）。
+2. **结果追加，不覆盖**：会议结果只能新增并指向 `supersedes_id`，绝不改写既有
+   记录或历史预测（BR-13 / AC-33）。
+"""
+
+from __future__ import annotations
+
+from typing import Literal
+
+from pydantic import Field, model_validator
+
+from contracts.prescreen import (
+    DESC_MAX,
+    EVIDENCE_MAX,
+    ID_MAX,
+    AwareDatetime,
+    Contract,
+    EventOutcome,
+    Ref,
+)
+
+STEP_KINDS = ("plan", "skill", "tool", "rule", "judgment", "synthesis")
+STEP_STATUSES = ("queued", "running", "completed", "skipped", "failed", "cancelled")
+
+
+class TrajectoryStep(Contract):
+    """一次运行里的一个可观察步骤。`failed` 步骤保留而不是被过滤掉。"""
+
+    id: str = Field(min_length=1, max_length=ID_MAX)
+    run_id: str = Field(min_length=1, max_length=ID_MAX)
+    parent_step_id: str | None = Field(default=None, max_length=ID_MAX)
+    sequence: int = Field(ge=0)
+    kind: Literal["plan", "skill", "tool", "rule", "judgment", "synthesis"]
+    component_ref: Ref | None = None
+    input_refs: list[str] = Field(default_factory=list, max_length=EVIDENCE_MAX)
+    output_refs: list[str] = Field(default_factory=list, max_length=EVIDENCE_MAX)
+    evidence_ids: list[str] = Field(default_factory=list, max_length=EVIDENCE_MAX)
+    status: Literal["queued", "running", "completed", "skipped", "failed", "cancelled"]
+    started_at: AwareDatetime | None = None
+    finished_at: AwareDatetime | None = None
+    reason_summary: str | None = Field(default=None, max_length=DESC_MAX)
+    error_code: str | None = Field(default=None, max_length=ID_MAX)
+    latency_ms: int | None = Field(default=None, ge=0)
+    cost: float | None = Field(default=None, ge=0)
+    cost_currency: str | None = Field(default=None, max_length=16)
+
+    @model_validator(mode="after")
+    def _check_step(self) -> TrajectoryStep:
+        if self.status == "failed" and not self.error_code:
+            raise ValueError("失败的步骤必须带错误码，不能只留一条看不出原因的记录")
+        if self.cost is None and self.cost_currency is not None:
+            raise ValueError("成本未知时币种也必须留空，不能只写币种")
+        if self.parent_step_id == self.id:
+            raise ValueError("步骤不能以自己为父步骤")
+        return self
+
+    def observable(self) -> dict:
+        """对外可读字段白名单：排除任何推理过程字段（AC-32 的机器可读断言）。"""
+        body = self.model_dump(mode="json")
+        return {key: body[key] for key in (
+            "id", "run_id", "parent_step_id", "sequence", "kind", "component_ref",
+            "input_refs", "output_refs", "evidence_ids", "status", "started_at",
+            "finished_at", "reason_summary", "error_code", "latency_ms", "cost",
+            "cost_currency")}
+
+
+class ReviewOutcome(Contract):
+    """评审会结果记录。`label` 只在口径明确时才有值，未确认的一律为空。"""
+
+    id: str = Field(min_length=1, max_length=ID_MAX)
+    project_id: str = Field(min_length=1, max_length=ID_MAX)
+    meeting_id: str = Field(min_length=1, max_length=ID_MAX)
+    revision: int = Field(ge=1)
+    occurred_at: AwareDatetime
+    recorded_at: AwareDatetime
+    reviewed_snapshot_id: str | None = Field(default=None, max_length=ID_MAX)
+    raw_code: str = Field(min_length=1, max_length=100)
+    normalized: EventOutcome
+    mapping_ref: Ref | None = None
+    label: bool | None = None
+    conditions: list[str] = Field(default_factory=list, max_length=50)
+    evidence_ids: list[str] = Field(default_factory=list, max_length=EVIDENCE_MAX)
+    status: Literal["matched", "unmatched"]
+    supersedes_id: str | None = Field(default=None, max_length=ID_MAX)
+    recorded_by: str = Field(min_length=1, max_length=ID_MAX)
+
+    @model_validator(mode="after")
+    def _check_outcome(self) -> ReviewOutcome:
+        if self.status == "unmatched" and self.reviewed_snapshot_id is not None:
+            raise ValueError("找不到对应材料版本时应记为 unmatched，不得挂上任何快照")
+        if self.status == "matched" and self.reviewed_snapshot_id is None:
+            raise ValueError("matched 必须指向被评审的材料版本")
+        if self.label is not None:
+            if self.mapping_ref is None or self.status != "matched":
+                raise ValueError("没有明确映射口径或材料版本未匹配时不得给出二元标签")
+            if self.normalized not in (EventOutcome.approved, EventOutcome.rejected):
+                raise ValueError("只有通过/否决才有二元标签；附条件、撤回、未送审一律留空")
+        if self.supersedes_id == self.id:
+            raise ValueError("更正不能指向自己")
+        return self
+
+    def counts_toward_denominator(self) -> bool:
+        """未送审、撤回、附条件、未知都不进入已观察通过率的分母（AC-22/37）。"""
+        return self.status == "matched" and self.normalized in (
+            EventOutcome.approved, EventOutcome.rejected)