Preserve V3 Sessions with incomplete child catalog evidence
保留子目录证据不完整的 V3 Session
A valid V3 child log can have no own descriptor, an unsupported descriptor version, or multiple descriptors. Its header still establishes its identity and parent relationship. Requiring one supported descriptor to migrate the parent makes unavailable discovery fields prevent access to otherwise readable history.
English
Problem
A valid V3 child log can have no own descriptor, an unsupported descriptor version, or multiple descriptors. Its header still establishes its identity and parent relationship. Requiring one supported descriptor to migrate the parent makes unavailable discovery fields prevent access to otherwise readable history.
Decision
The V3→V4 migration appends a complete missing parent catalog entry only when exactly one supported own child descriptor supplies its discovery fields. Other descriptor counts and unsupported versions retain unknown-mode membership through session-local catalog preparation. Existing parent entries and child events remain intact. This replaces only the missing-evidence refusal in the adjacent migration decision.
The JSONL failure-propagation rules below are partially superseded by session-local catalog preparation; the converter still validates supplied facts and conflicts. Known child creation times must still match existing parent entries. Mode/label and descriptor fields are checked only for exactly one supported own descriptor. JSONL isolates invalid descriptor fields and corrupt child bodies while retaining known header identity; unreadable or unsupported headers are excluded from discovery. Changed source revisions still refuse publication.
Alternatives considered
Refuse the whole parent. Discovery metadata is insufficient to justify making valid parent history unavailable.
Choose the first or last descriptor. foldSubagentDescriptor() takes the first under the establishing provider’s exactly-once rule; the identity projection takes the last to override inherited identities. Multiple own records violate that rule. Backfill requires one own record rather than choosing between these consumer policies.
Infer missing fields. Invented mode or label fields would become durable catalog facts without evidence.
Consequences
A historical child with a readable header but no usable descriptor retains unknown-mode membership in its parent's direct-child catalog. Existing catalog entries remain visible. Once a V4 successor is published, opening it does not rescan historical children; automatic later mode backfill is outside this migration. Preparation still rechecks child revisions before publication, so newly available evidence cannot silently bypass source consistency checks.
Unit, JSONL read/write, and Preview packing tests cover unavailable evidence, unchanged source bytes, retained entries, identity conflicts, and evidence changes before publication.
中文
Problem
有效 V3 子日志可能没有自身 descriptor、descriptor 版本不受支持，或存在多个 descriptor。其 header 仍能确定身份及父子关系。要求一个受支持的 descriptor 才迁移父日志，会让不可获得的发现字段阻止读取原本可读的历史。
Decision
V3→V4 迁移仅在恰好一个受支持的自身子 descriptor 提供发现字段时，追加完整的缺失父目录项。其他 descriptor 数量和不支持的版本通过逐会话目录准备保留模式未知的成员关系。已有父目录项和子事件保持不变。这取代相邻迁移决策中对缺失证据的拒绝。
JSONL 错误传播规则由逐会话目录准备部分取代；转换器仍校验已提供事实及冲突。已知子创建时间必须匹配已有父目录项。只有恰好一个受支持的自身 descriptor 时才检查 mode／label 和 descriptor 字段。JSONL 隔离无效 descriptor 字段和损坏子正文，并保留已知 header 身份；不可读或不支持的 header 不参与发现。来源修订变化仍拒绝发布。
Alternatives considered
拒绝整个父 Session。 发现元数据不足以成为禁止读取有效父历史的理由。
选择首个或末个 descriptor。 foldSubagentDescriptor() 依据建立提供方恰好写入一次的规则取首个；身份投影取末个以覆盖继承身份。多个自身记录违反该规则。补填要求一个自身记录，而不在这两种消费者策略之间做选择。
推断缺失字段。 推断的 mode 或 label 会在没有证据的情况下成为持久目录事实。
Consequences
历史子会话具有可读 header 但没有可用 descriptor 时，在父直属子目录中保留未知模式成员关系。已有目录项仍可见。V4 后继发布后，打开它不重新扫描历史子日志；自动补齐后续模式不属于本迁移。准备过程仍在发布前重新检查子修订，因此新出现的证据不能静默绕过来源一致性检查。
单元、JSONL 读写和 Preview 打包测试覆盖不可用证据、源字节不变、条目保留、身份冲突以及发布前的证据变化。