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111 lines
7.2 KiB
Markdown
111 lines
7.2 KiB
Markdown
# 会话持久化
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[English](persistence.md) | 中文
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事件日志的**持久性 seam**。[session.md](session.md) 描述了内存中的 `Session`：仅追加的 `SessionEvent` 日志即为真源。本页描述如何使该日志持久化：抽象的 `SessionPersistence` 服务、它的后端、flush 检查点、崩溃恢复，以及随日志一同存储的元数据头。日志承载的事件词汇在生成的[持久化日志事件目录](../persistence-catalog.md)中逐项列举。
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该 seam 是典型的[能力 seam](../../.agents/notes/implemented/architecture/2026-06-13-capability-seams.md)：一个抽象服务（[dsh-session-persistence](../../packages/session-persistence/session-persistence)，`ctx.sessionPersistence`）在现有 `SessionEvent` 上定义 locate/create/append/load/list——**没有平行的持久化类型**——以及两个可互换、通过同一套 `runPersistenceContract` 的后端。见 [session-persistence Agent Note（agent 决策记录）](../../.agents/notes/implemented/architecture/2026-06-14-session-persistence.md)。
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## flush 检查点
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`session/event` 是一个*同步*通知；持久化插件会将其缓冲（write-behind）至 `session/flush`。循环会 await 普通轮次的检查点后再领取下一个队列项；同步的 idle `inject()` 会调度自己的检查点而不阻塞 `send()`，dispose（资源释放）仍会将其排空。成功 flush 会把已关闭轮次作为一个单元持久提交；被拒绝的 flush 通过 `agent/error` 与 logger 报告——绝不会作为已关闭轮次之后的会话事件——而后端会保留已缓冲事件供下次 flush 使用。
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## 崩溃恢复保留被中断的轮次
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后端重新加载一个在轮次中途崩溃的日志时，会发现一个已打开的 `turn/start` 却没有 `turn/end`。它**不会**截断日志：在长周期任务中，单个轮次可能非常庞大（许多步骤、大量工具输出），而这些事件在崩溃前已被持久追加。后端改为用一个合成的 `turn/end { reason: { kind: 'interrupted' } }` 关闭这个遗留轮次，保持日志平衡与轮次闭合不变式。`interrupted` 是唯一一个不由循环发出的 `TurnEndReason`（见 [session.md](session.md#why-a-turn-ended-turnendreasonmap)）。
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## `SessionLocation`——可选的逐会话产物目标
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`SessionPersistence.locate(meta)` 会同步解析一个归后端所有的独立产物，而不会读取、创建或 flush 它。JSONL 返回其绝对目标路径；SQLite 因各会话共享一个数据库而返回 `undefined`。因此，返回的路径可能指向尚不存在、或还不包含当前尚未 flush 的轮次；它是位置提示，不是授权或新鲜度保证。
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```ts type-equiv
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/**
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* A backend-resolved, per-session local artifact location. The path is an
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* absolute target path and can name an artifact that has not materialized yet.
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* Consumers must treat it as a location hint, never as an authorization token.
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*/
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interface SessionLocation {
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/** Backend-specific artifact kind, for example `jsonl`. */
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readonly kind: string
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/** Absolute path to this session's backend-owned artifact. */
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readonly path: string
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}
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```
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## `SessionHeader`：日志旁的元数据
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每个会话的元数据与事件日志**分开**存储：格式版本、cwd、血统与 seed 边界是存储层关注点而非对话事件，因此不进入 `SessionEventMap`，也不会到达 `deriveMessages()`。header 通过 `session.header` 附加到 `Session` 上。
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源码：[`packages/core/session/src/types.ts`](../../packages/core/session/src/types.ts)
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```ts type-equiv
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/**
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* Immutable validated storage metadata, kept outside the conversation event log.
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*/
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interface SessionHeader {
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/**
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* On-disk format version, stamped from {@link SESSION_FORMAT_VERSION} when the
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* session is created. A persistence backend rejects any other version on load
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* (no migration — see the constant).
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*/
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readonly version: number
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/** The session's id (mirrors the {@link Session}'s id). */
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readonly id: SessionId
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/** Unix epoch milliseconds when the session was created. */
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readonly createdAt: number
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/** Absolute working directory the session was created in (if any). */
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readonly cwd?: string
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/** The session this one was forked from (seed lineage), if any. */
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readonly parentSession?: SessionId
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/**
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* How many leading events were inherited through a seed. Persisting this
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* boundary lets resume and replay distinguish parent history from child work.
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*/
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readonly seedLength?: number
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/**
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* Delegation depth: absent (zero) for a top-level session, parent depth + 1
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* for a subagent child. Persisted so a recursion budget survives restart and
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* resume — a runtime-only depth would reset a resumed child to top-level.
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*/
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readonly delegationDepth?: number
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}
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```
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## `CreateSessionOptions`：seed 与元数据
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通过 store 创建 `Session` 时会接收 `seed`（回放/fork 现有事件日志）与 `meta`（store 折叠进 `SessionHeader` 的存储层字段）。store 填充 `version`/`id` 并为 `createdAt` 提供默认值；调用方提供已校验的绝对 `cwd`、`parentSession` 谱系、`seedLength` 种子边界、`delegationDepth`，以及——仅在重建已持久化会话时——需要保留的原始 `createdAt`。
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```ts type-equiv
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/**
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* Options for creating a {@link Session} via the store. `seed` replays/forks
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* an existing event log; `meta` carries the caller-supplied storage fields the
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* store folds into a {@link SessionHeader}.
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*/
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interface CreateSessionOptions {
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/** Events to seed the new session with (replay/fork). */
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readonly seed?: readonly SessionEvent[]
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/**
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* Storage metadata read once before publication. `seedLength` is explicit
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* because a resumed seed contains the full stored log, not only its inherited prefix.
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*/
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readonly meta?: {
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readonly cwd?: string
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readonly parentSession?: SessionId
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readonly createdAt?: number
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readonly seedLength?: number
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readonly delegationDepth?: number
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}
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}
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```
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因此，回放/fork 的调用方式为 `ctx.sessions.create(id, { seed: seedEvents })`；将一个*持久化*会话恢复为活跃 agent 的调用方式为 `ctx.agents.resume({ resumeSessionId })`。
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## 后端
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两者都实现同一个抽象 `SessionPersistence`（在 `SessionEvent` 上执行 locate/create/append/load/list），并通过 `runPersistenceContract`，证明该 seam 确实与后端无关：
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- **[dsh-session-persistence-jsonl](../../packages/session-persistence/session-persistence-jsonl)**——每个会话一份仅追加的逻辑 JSONL 日志，默认存储为带 checksum 的连续 Zstandard frame，也可配置为原始行；支持崩溃安全的原子写入、被中断轮次的恢复以及读取/回放路径。
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- **[dsh-session-persistence-sqlite](../../packages/session-persistence/session-persistence-sqlite)**：基于 `node:sqlite`，每个 `SessionEvent` 一行。行结构 `(session_id, seq, type, time, data, source_event_seqs, surface_op)` 与事件 1:1 映射（包含可选的 surface 元数据），因此没有需要保持同步的并行持久化 schema。
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共享同一磁盘会话的多个后端通过[共享持久化写入协调器](../../.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md)协调写入。
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