docs: document session preparation flow

packages/session-persistence/session-persistence/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/session-persistence/session-persistence/README.md
-README.md: 65b50c41670c400284f52c57795b2be49bf21117
-README.zh.md: 7497da2bd6ca03b78d769c1df9995ceb925fdacc
+README.md: 4c00c28184c0046d5507270980822529bfe3bc08
+README.zh.md: 32461cec5efd279a86bf3af40b23e7e54d33a89e

packages/session-persistence/session-persistence/README.md

@@ -13,9 +13,10 @@ The persisted unit IS the existing `SessionEvent` (event-sourced model — the l
 | `locate(meta): SessionLocation \| undefined` | Resolve an absolute per-session artifact target without I/O or materialization. Backends without an independent local artifact return `undefined`. |
 | `create(meta): Promise<void>` | Register a new session's metadata. MAY defer the physical write until the first `append` (lazy materialization). |
 | `append(id, events): Promise<void>` | Durably persist a batch. Append-only; first event `seq` == stored next-seq after any repair; rejects non-JSON-serializable data naming the offending type. |
-| `load(id): Promise<{ meta; events }>` | Return a stored header plus a balanced contiguous log whose events are detached and validated and whose identified messages are deeply frozen. The coordinator upgrades the supported same-version message and pre-react-loop event shapes into the current read snapshot; all other obsolete or malformed shapes still reject. A live load first flushes its snapshot and rejects while its turn is open; a cold load preserves an interrupted final turn and closes it with synthetic `tool/result`/`step/end?`/`turn/end {interrupted}` events. Only a torn tail fragment is dropped; committed corruption and unknown `version` reject. |
-| `inspect(id, signal?): Promise<{ meta; events }>` | Return a detached valid stored prefix with upgraded, validated, deeply frozen identified messages, without truncating a torn tail, synthesizing recovery closers, or publishing coordinator state. Serialized with same-id writes; the optional signal promptly rejects a queued caller, prevents that queued backend read from starting, and cancels active backend read work. Intended for read models and other observers that must never recover a log. |
-| `readFrom(id, fromSeq, signal?): Promise<{ meta; events }>` | The read-from-seq primitive: return the header plus the valid stored events with `seq >= fromSeq`, detached and non-mutating like `inspect` (no truncation, no closers, no coordinator state). A `fromSeq` at or past the stored end returns an empty event list; a negative or non-safe-integer `fromSeq` rejects. Seek-capable backends (SQLite) read only the suffix unless a legacy event in that suffix requires prefix context for normalization; sequential backends (JSONL) parse the whole artifact and skip forward. Intended for checkpoint consumers (e.g. the persisted projection cache) that fold only the tail past a watermark. |
+| `prepare(id, signal?): Promise<SessionPreparation>` | Reserve the exact unpublished Session used by resume. A coordinator reuses an earlier inspection when available, commits pending recovery, and releases an unpublished reservation back to its bounded cache on disposal. |
+| `load(id): Promise<{ meta; events }>` | Return an immutable balanced logical log after supported same-version shape upgrades and commit cold recovery. A live load first flushes its snapshot and rejects while its turn is open; a cold load preserves an interrupted final turn and durably closes it with synthetic `tool/result`/`step/end?`/`turn/end {interrupted}` events. Only a torn tail fragment is dropped; committed corruption, malformed shapes, and unknown `version` reject. |
+| `inspect(id, signal?): Promise<{ meta; events }>` | Return the same upgraded, validated, deeply frozen logical view without committing recovery or publishing a Session. Synthetic recovery closers exist only in memory, the physical torn tail remains untouched, and coordinator-backed implementations retain the exact unpublished Session in a bounded LRU for later `prepare`. Same-id inspections share an in-flight read. |
+| `readFrom(id, fromSeq, signal?): Promise<{ meta; events }>` | The detached physical-suffix primitive: return valid stored events with `seq >= fromSeq` without preparation caching, truncation, closers, or coordinator state. A `fromSeq` at or past the stored end returns an empty event list; a negative or non-safe-integer `fromSeq` rejects. Seek-capable backends (SQLite) read only the suffix unless a supported old shape requires prefix context for normalization; sequential backends (JSONL) parse the whole artifact and skip forward. Intended for checkpoint consumers that fold only the tail past a watermark. |
 | `list(signal?): Promise<SessionHeader[]>` | Lightweight listing from metadata, no full-log parse. The optional signal cancels backend listing work. A zero-event lazily-materialized session is absent from `list`. |
 | `listSnapshots(signal?): Promise<SessionPersistenceSnapshot[]>` | Lightweight metadata plus an opaque branded per-log revision, without loading event logs. A revision stays equal while that log and its backing store are unchanged, changes after append or mutating load repair, and cannot collide solely because two stores use the same local counter. The optional signal requests cancellation of backend discovery work; first-party backends settle any started listing work before rejecting so an awaited call is quiescent. |
 
@@ -32,7 +33,7 @@ The persisted unit IS the existing `SessionEvent` (event-sourced model — the l
 
 Each `session/event` copies its event into the session controller and starts an eager drain without blocking the producer. Concurrent notifications share the current drain; events admitted during a write remain pending and trigger the next batch. `session/flush` is an observation barrier that waits until the controller has no current or pending batch. An eager failure is logged and retains the batch; the next explicit flush or backend teardown retries it and surfaces failure to its caller.
 
-Crash repair is cold-only. For a live id, `load(id)` snapshots the authoritative in-memory log, waits for that snapshot to become durable, and returns it with the coordinator's stored header only when balanced; an open live turn rejects instead of receiving synthetic interruption closers. A cold load reserves its id across backend reads and repair writes, so concurrent publication of a same-id live `Session` rejects and rolls back. HMR adoption reads through `loadStored`, applies the coordinator's cwd check, and never closes the active turn.
+Crash repair is cold-only. For a live id, `load(id)` snapshots the authoritative in-memory log, waits for that snapshot to become durable, and returns it only when balanced; an open live turn rejects instead of receiving synthetic interruption closers. For a cold id, inspection reads, validates, freezes, and constructs one unpublished Session; repeated inspection reuses that object graph. `prepare(id)` reserves the exact Session, commits any pending torn-tail/interrupted-turn repair, and returns it for publication. HMR adoption reads through `loadStored`, applies the coordinator's cwd check, and never closes the active turn.
 
 Backend reads normalize the exact supported same-version shapes before current-shape validation. Pre-identity messages receive the deterministic id `legacy-message:<session-id>:<event-seq>`; a tool-result content replacement inherits its target's imported id. A pre-react-loop `turn/start` loses its obsolete trigger, a removed `steering/message` becomes the same identified `user/message`, and an older `turn/end` maps its terminal reason without inventing unavailable cancellation provenance. The coordinator uses the same normalized view for `load`, `inspect`, `readFrom`, ownerless-state claims, and HMR prefix adoption. Storage remains append-only: reads do not rewrite old records, and later appends use the current shape. These are narrow import exceptions from the [pre-identity message](../../../.agents/notes/implemented/bug-fix/2026-07-28-load-pre-identity-session-messages.md) and [pre-react-loop session](../../../.agents/notes/implemented/bug-fix/2026-08-04-load-pre-react-loop-sessions.md) decisions, not a general v0 migration promise.
 
@@ -52,7 +53,7 @@ The `PersistenceBackend<TornMarker>` hooks (the only seam between the coordinato
 | `list(signal?)` | List all stored metadata, observing optional cancellation. |
 | `close?()` | Optional lifecycle teardown (e.g. close a db handle), awaited after the dispose drain. |
 
-The coordinator asserts the stored id and compares stored/live cwd before repair or live adoption. Its `inspect()` path validates and clones the prefix without calling `commitRepair` or publishing write state. The `tornMarker` is fully OPAQUE: the coordinator only tests `!== undefined` and round-trips it to `commitRepair`, never inspecting its value (the JSONL backend uses the byte offset to truncate to, the SQLite backend the seq to delete from). A third-party backend MAY implement the abstract service directly without the coordinator, but it must provide the same non-mutating inspection and trustworthy lightweight snapshot revisions. See [the write-coordinator Agent Note](../../../.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md).
+The coordinator asserts the stored id and compares stored/live cwd before repair or live adoption. Its `inspect()` path takes ownership of fresh backend values, validates and freezes them once, and retains at most the configured number of unpublished Sessions without calling `commitRepair`. The `tornMarker` is fully OPAQUE: the coordinator only tests `!== undefined` and round-trips it to `commitRepair`, never inspecting its value (the JSONL backend uses the byte offset to truncate to, the SQLite backend the seq to delete from). A third-party backend MAY implement the abstract service directly without the coordinator, but it must provide the same non-mutating inspection and trustworthy lightweight snapshot revisions. See [the write-coordinator Agent Note](../../../.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md).
 
 ## Metadata and location types
 

packages/session-persistence/session-persistence/README.zh.md

@@ -13,9 +13,10 @@
 | `locate(meta): SessionLocation \| undefined` | 在不执行 I/O 或实体化的情况下解析绝对的每会话产物目标。没有独立本地产物的后端返回 `undefined`。 |
 | `create(meta): Promise<void>` | 注册新会话元数据。可以将物理写入延迟到第一次 `append`（延迟实体化）。 |
 | `append(id, events): Promise<void>` | 持久保存一个批次。仅追加；任何修复后，第一个事件 `seq` == 已存储 next-seq；非 JSON 可序列化数据会被拒绝，并命名违规类型。 |
-| `load(id): Promise<{ meta; events }>` | 返回已存储 header 和平衡、连续的日志，其中事件已脱离并验证，带标识的消息已深度冻结。协调器会将受支持的同版本消息形状与 react-loop 重构前的事件形状升级为当前读取快照；其余过时或格式错误的形状仍会被拒绝。实时 load 先 flush 其快照，并在轮次开放时拒绝；冷 load 保留中断的最终轮次，并用合成 `tool/result`/`step/end?`/`turn/end {interrupted}` 事件关闭它。只丢弃撕裂尾部碎片；已提交损坏和未知 `version` 会被拒绝。 |
-| `inspect(id, signal?): Promise<{ meta; events }>` | 返回脱离的有效已存储前缀，其中带标识的消息已经升级、验证并深度冻结；不截断撕裂尾部、合成恢复 closer 或发布协调器状态。它与同 id 写入串行化；可选信号会迅速拒绝已排队调用方，阻止该后端读取启动，并取消活动后端读取工作。用于绝不应恢复日志的读模型和其他观察者。 |
-| `readFrom(id, fromSeq, signal?): Promise<{ meta; events }>` | read-from-seq 原语：返回 header 和 `seq >= fromSeq` 的有效已存储事件，与 `inspect` 同样脱离且非变更（不截断、不合成 closer、不发布协调器状态）。`fromSeq` 达到或超过已存储末尾时返回空事件列表；负数或非安全整数 `fromSeq` 会被拒绝。可寻址后端（SQLite）只读后缀，除非后缀中的旧版事件需要前缀上下文才能完成规范化；顺序后端（JSONL）会解析整个产物并向前跳过。用于从水位续折尾部的 checkpoint 消费方（例如持久投影缓存）。 |
+| `prepare(id, signal?): Promise<SessionPreparation>` | 预留恢复使用的精确未发布 Session。协调器会尽可能复用之前的检查结果、提交待处理恢复，并在 dispose 时将未发布 reservation 释放回有界缓存。 |
+| `load(id): Promise<{ meta; events }>` | 在升级受支持的同版本形状后返回不可变、平衡的逻辑日志，并提交冷恢复。实时 load 先 flush 其快照，并在轮次开放时拒绝；冷 load 保留中断的最终轮次，并用合成 `tool/result`/`step/end?`/`turn/end {interrupted}` 事件持久关闭它。只丢弃撕裂尾部碎片；已提交损坏、格式错误的形状和未知 `version` 会被拒绝。 |
+| `inspect(id, signal?): Promise<{ meta; events }>` | 返回同一份已经升级、验证和深度冻结的逻辑视图，但不提交恢复或发布 Session。合成恢复 closer 只存在于内存，物理撕裂尾部保持不变，基于协调器的实现会在有界 LRU 中保留精确的未发布 Session，供后续 `prepare` 使用。同 id 检查共享进行中的读取。 |
+| `readFrom(id, fromSeq, signal?): Promise<{ meta; events }>` | 脱离的物理后缀原语：返回 `seq >= fromSeq` 的有效已存储事件，不进入 preparation 缓存、不截断、不合成 closer，也不发布协调器状态。`fromSeq` 达到或超过已存储末尾时返回空事件列表；负数或非安全整数 `fromSeq` 会被拒绝。可寻址后端（SQLite）只读后缀，除非受支持的旧形状需要前缀上下文才能完成规范化；顺序后端（JSONL）解析整个产物并向前跳过。用于只续折水位之后尾部的 checkpoint 消费方。 |
 | `list(signal?): Promise<SessionHeader[]>` | 从元数据轻量列出，不解析完整日志。可选信号取消后端列表工作。零事件延迟实体化会话不在 `list` 中。 |
 | `listSnapshots(signal?): Promise<SessionPersistenceSnapshot[]>` | 返回轻量元数据和每份日志一个不透明、带品牌类型的修订值，不加载事件日志。日志及其后端存储不变时，修订保持相等；append 或变更性 load 修复后会改变；不会仅因两个存储使用相同本地计数器而冲突。可选信号请求取消后端发现工作；第一方后端会先等待所有已启动的列出工作结束，再予以拒绝，因此调用返回拒绝时，相关工作已完全停稳。 |
 
@@ -32,7 +33,7 @@
 
 每个 `session/event` 将事件复制到会话 controller，并在不阻塞生产者的情况下立即启动 drain。并发通知共享当前 drain；写入期间接纳的事件保持 pending，并触发下一批。`session/flush` 是观察屏障，会等待 controller 无当前或 pending 批次。即时写入失败会记录日志并保留批次；下一次显式 flush 或后端拆卸会重试该批次，并将失败返回给调用方。
 
-崩溃修复只适用于冷状态。对于实时 id，`load(id)` 为权威内存日志制作快照，等待该快照持久，并只在平衡时将其与协调器已存储 header 一起返回；开放实时轮次会被拒绝，而不会收到合成中断 closer。冷 load 在后端读取和修复写入期间保留 id，因此同 id 实时 `Session` 的并发发布会拒绝并回滚。HMR 接管通过 `loadStored` 读取，应用协调器 cwd 检查，并绝不关闭活动轮次。
+崩溃修复只适用于冷状态。对于实时 id，`load(id)` 为权威内存日志制作快照，等待该快照持久，并只在平衡时返回；开放实时轮次会被拒绝，而不会收到合成中断 closer。对于冷 id，检查只读取、验证、冻结并构造一次未发布 Session；重复检查会复用该对象图。`prepare(id)` 预留精确 Session，提交任何待处理的撕裂尾部或中断轮次修复，并将其返回用于发布。HMR 接管通过 `loadStored` 读取，应用协调器 cwd 检查，并绝不关闭活动轮次。
 
 后端读取会在当前形状验证前，规范化明确受支持的同版本形状。消息标识机制引入前的消息会获得确定性的 id `legacy-message:<session-id>:<event-seq>`；工具结果的内容替换会继承其目标导入后的 id。react-loop 重构前的 `turn/start` 会移除过时的 trigger，已移除的 steering（中途引导）事件 `steering/message` 会转换为同一条带标识的 `user/message`；旧版 `turn/end` 会在不虚构无法获得的取消来源的前提下映射终止原因。协调器对 `load`、`inspect`、`readFrom`、无 owner 状态的认领和 HMR 前缀接管使用同一份规范化视图。存储仍然仅追加：读取不会重写旧记录，此后追加的事件使用当前形状。这些是[消息标识机制引入前的消息](../../../.agents/notes/implemented/bug-fix/2026-07-28-load-pre-identity-session-messages.md)与 [react-loop 重构前会话](../../../.agents/notes/implemented/bug-fix/2026-08-04-load-pre-react-loop-sessions.md)决策所规定的范围受限的导入例外，并不构成通用的 v0 迁移承诺。
 
@@ -52,7 +53,7 @@
 | `list(signal?)` | 列出全部已存储元数据，并遵循可选的取消信号。 |
 | `close?()` | 可选生命周期拆卸（例如关闭 db 句柄），在 dispose drain 后等待。 |
 
-协调器断言已存储 id，并在修复或实时接管前比较已存储/实时 cwd。其 `inspect()` 路径验证并克隆前缀，不调用 `commitRepair` 或发布写入状态。`tornMarker` 完全不透明：协调器只测试 `!== undefined`，并将其原样往返给 `commitRepair`，绝不检查值（JSONL 后端使用待截断字节偏移，SQLite 后端使用待删除 seq）。第三方后端可以不用协调器直接实现抽象服务，但必须提供相同非变更检查和可信轻量快照修订。详见[写入协调器 Agent Note](../../../.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md)。
+协调器断言已存储 id，并在修复或实时接管前比较已存储/实时 cwd。其 `inspect()` 路径取得新鲜后端值的所有权，只验证和冻结一次，并在不调用 `commitRepair` 的情况下最多保留配置数量的未发布 Session。`tornMarker` 完全不透明：协调器只测试 `!== undefined`，并将其原样往返给 `commitRepair`，绝不检查值（JSONL 后端使用待截断字节偏移，SQLite 后端使用待删除 seq）。第三方后端可以不用协调器直接实现抽象服务，但必须提供相同非变更检查和可信轻量快照修订。详见[写入协调器 Agent Note](../../../.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md)。
 
 ## 元数据与位置类型