docs(session): record synchronous history read deprecation policy

.agents/notes/implemented/architecture/2026-06-11-dev-invariants-over-deep-readonly.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 .agents/notes/implemented/architecture/2026-06-11-dev-invariants-over-deep-readonly.md
-2026-06-11-dev-invariants-over-deep-readonly.md: 9adb741db1e26e3a9f750fed60524351159cfeaa
-2026-06-11-dev-invariants-over-deep-readonly.zh.md: d352eca985b6594ec5d10c9b73c2ecc18ea458b5
+2026-06-11-dev-invariants-over-deep-readonly.md: 0784960397f4d198e136e284ef9232b4ed3e2c2c
+2026-06-11-dev-invariants-over-deep-readonly.zh.md: 7183813130560bf82426c8719570b668ba86b7e5

.agents/notes/implemented/architecture/2026-06-11-dev-invariants-over-deep-readonly.md

@@ -22,7 +22,7 @@ Responsibility is split between an always-on storage boundary and optional devel
 
 `Session` accepts an event only after one recursive pass has materialized a lossless JSON snapshot. That pass rejects unsupported values and produces the exact detached record that enters the log, so validation and storage cannot observe different values from a stateful getter or retain caller-owned nested references.
 
-The accepted event and all of its descendants are deep-frozen before publication. `append()` returns that owned frozen event, and `session/event` observers and `eventAt(seq)` receive the same record. `snapshotEvents(fromSeq?, toSeqExclusive?)` returns a frozen array snapshot; a previously returned array does not grow after a later append. `seq` and `eventAt()` avoid array materialization when a caller needs only the current length or one event. Seed records pass through the same validation, snapshot, and freeze boundary before construction succeeds.
+The accepted event and all of its descendants are deep-frozen before publication. `append()` returns that owned frozen event, and `session/event` observers and `eventAt(seq)` receive the same record. `snapshotEvents(fromSeq?, toSeqExclusive?)` returns a frozen array snapshot; a previously returned array does not grow after a later append. `seq` reads the current length without materializing an array. Synchronous historical readers are deprecated under the [event-read policy](2026-09-09-deprecate-synchronous-session-event-reads.md). Seed records pass through the same validation, snapshot, and freeze boundary before construction succeeds.
 
 This guarantee belongs in `Session`, not in an optional listener, because every composition relies on trustworthy history. A production deployment, a focused test, or a custom embedding receives the same storage semantics whether or not development support plugins are registered.
 
@@ -53,7 +53,7 @@ Detaching `deriveMessages()` would protect the most common request path but leav
 ## Consequences
 
 - Every accepted live or seeded session event is detached from caller-owned inputs and deeply immutable before any observer can receive it.
-- `snapshotEvents()` exposes stable immutable snapshots instead of the private growing array; `seq` and `eventAt()` serve scalar reads without copying that array.
+- Existing `snapshotEvents()` and `eventAt()` callers retain immutable read results while their migration is deferred; `seq` reads the log length without copying the array.
 - Request-side mutation cannot reach stored history through derived messages.
 - Development builds can enable relational assertions without changing storage behavior, and disposing or filtering a companion does not weaken log immutability.
 - `dsh-invariants` configures global enablement plus package allow/block regex lists; each check remains owned and tested by its product package.

.agents/notes/implemented/architecture/2026-06-11-dev-invariants-over-deep-readonly.zh.md

@@ -22,7 +22,7 @@ TypeScript readonly 类型不是充分的运行时边界。它们在程序运行
 
 `Session` 仅在一次递归遍历完成无损 JSON 快照的物化之后才接受事件。该遍历拒绝不支持的值，并产出进入日志的已分离的确切记录，因此验证与存储不会从有状态的 getter 观察到不同的值，也不会保留调用方拥有的嵌套引用。
 
-被接受的事件及其所有后代在发布前被深度冻结。`append()` 返回由 Session 拥有的冻结事件，`session/event` 观察者和 `eventAt(seq)` 接收同一记录。`snapshotEvents(fromSeq?, toSeqExclusive?)` 返回冻结的数组快照；先前返回的数组不会因后续 append 而增长。调用方只需要当前长度或单个事件时，`seq` 和 `eventAt()` 不会物化数组。种子记录在构造成功前经过相同的验证、快照与冻结边界。
+被接受的事件及其所有后代在发布前被深度冻结。`append()` 返回由 Session 拥有的冻结事件，`session/event` 观察者和 `eventAt(seq)` 接收同一记录。`snapshotEvents(fromSeq?, toSeqExclusive?)` 返回冻结的数组快照；先前返回的数组不会因后续 append 而增长。`seq` 无需物化数组即可读取当前长度。同步历史读取方法按[事件读取策略](2026-09-09-deprecate-synchronous-session-event-reads.zh.md)弃用。种子记录在构造成功前经过相同的验证、快照与冻结边界。
 
 此保证属于 `Session` 而非可选监听器，因为每种组合都依赖可信的历史。无论是否注册了开发支持插件，生产部署、聚焦测试或自定义嵌入都获得相同的存储语义。
 
@@ -53,7 +53,7 @@ TypeScript readonly 类型不是充分的运行时边界。它们在程序运行
 ## 后果
 
 - 每个被接受的实时或种子会话事件在任何观察者接收之前，都已从调用方拥有的输入中分离并深度不可变。
-- `snapshotEvents()` 暴露稳定的不可变快照，而非持续增长的私有数组；`seq` 和 `eventAt()` 为标量读取提供无需复制数组的路径。
+- 现有 `snapshotEvents()` 和 `eventAt()` 调用方在暂缓迁移期间仍获得不可变的读取结果；`seq` 无需复制数组即可读取日志长度。
 - 请求侧的修改无法通过派生消息触及已存储的历史。
 - 开发构建可以启用关系断言而不改变存储行为；dispose 或过滤一个配套插件不会削弱日志不可变性。
 - `dsh-invariants` 配置全局启用状态以及包名允许/阻止 regex 列表；每项检查仍由其产品包拥有并测试。

.agents/notes/implemented/architecture/2026-09-09-deprecate-synchronous-session-event-reads.i18n.yaml

@@ -0,0 +1,6 @@
+# Bilingual-pair consistency record (docs/i18n/README.md): the git blob hash of each
+# 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 .agents/notes/implemented/architecture/2026-09-09-deprecate-synchronous-session-event-reads.md
+2026-09-09-deprecate-synchronous-session-event-reads.md: b0bc1e81ada1781587b7bd6b5687d62bc0d8e798
+2026-09-09-deprecate-synchronous-session-event-reads.zh.md: 0c8fd24bb48e6a40309fe571fce5d2fba5b99b2b

.agents/notes/implemented/architecture/2026-09-09-deprecate-synchronous-session-event-reads.md

@@ -0,0 +1,45 @@
+# Agent Note: Deprecate synchronous reads of arbitrary Session events
+
+Status: implemented
+
+English | [中文](2026-09-09-deprecate-synchronous-session-event-reads.zh.md)
+
+## Problem
+
+Synchronous access to arbitrary event positions makes consumers depend on the complete Session event sequence being immediately available in memory. The storage direction is to stop retaining that complete sequence in memory. Once historical events require storage I/O, the runtime cannot preserve the same synchronous read guarantee without retaining the history or blocking on storage.
+
+New callers increase that dependency even when they read only one old event. Repeated history scans after resume also make ordinary domain logic depend on historical storage instead of the state it actually needs.
+
+## Decision
+
+All operations that synchronously read arbitrary positions or ranges of Session event history are deprecated, including `Session.eventAt()`, `Session.snapshotEvents()`, and `Session.ownEvents()`. Existing logic may remain unmigrated for now, but new calls are prohibited. New aliases or wrappers that expose the same synchronous historical access are prohibited as well.
+
+The three methods carry this rule in `@deprecated` JSDoc. This is an API-use decision; the current Session implementation still retains the complete event sequence in memory.
+
+### State needed after resume
+
+Design durable event fields and Session projections together so each domain can reconstruct the state its consumers need. Restore that state during resume, then maintain it incrementally from newly committed events. After resume, ordinary logic reads the projection or processes the delivered current event instead of looking back through historical events. Reading already-maintained projection state synchronously does not require arbitrary access to the event log.
+
+Historical content presented on demand uses explicit asynchronous pagination and progressive loading, with each read limited to the requested window. Loading the complete sequence behind a synchronous helper preserves the dependency this decision removes.
+
+### Operations that require complete history
+
+Fork and a small number of operations may genuinely need a complete historical sequence or inherited prefix. Their need for those records remains valid and requires an explicit storage read. It does not require the whole sequence to remain resident or grant an exception for new calls to deprecated synchronous readers. Each such consumer must establish why its result requires the complete sequence rather than projected state or a limited historical window.
+
+## Alternatives considered
+
+**Keep synchronous single-event reads while deprecating only full snapshots.** A single requested event may also be absent from memory. Restricting the result size does not remove the storage dependency, and helpers such as `ownEvents()` retain the same assumption for a suffix.
+
+**Keep the complete sequence resident to preserve the read APIs.** This lets consumer convenience dictate Session memory retention and prevents the intended storage design. Projections preserve required state, while explicit historical reads preserve access to the records themselves.
+
+**Require every existing caller to migrate immediately.** Existing logic may defer migration under this decision. Preventing new dependencies bounds the remaining work without making every existing consumer part of the same change.
+
+## Consequences
+
+New domain behavior must make its event data and projected state sufficient for resumed execution. User-requested history may still load progressively, and genuine full-history operations still have a storage path to design. This decision does not claim that resume or fork already avoids loading the complete log.
+
+The current `typescript/no-deprecated` lint rule reports both existing and new calls. The JSDoc records the migration deferral, but lint does not yet distinguish permitted existing callers from prohibited additions. The documentation checks verify the source-equivalent API declarations and bilingual records; they do not enforce that distinction.
+
+## Related decisions
+
+The [session immutability decision](2026-06-11-dev-invariants-over-deep-readonly.md) continues to own event ownership and freezing; this decision supersedes its recommendation to use synchronous historical readers. The [required projection reader decision](2026-08-19-session-projection-mandatory-seam.md) continues to own missing-state failures and typed state reads. The [recallable compaction proposal](../../proposed/feature/2026-07-06-recallable-compaction.md) retains its recall design while replacing its proposed synchronous history access with paged reads.

.agents/notes/implemented/architecture/2026-09-09-deprecate-synchronous-session-event-reads.zh.md

@@ -0,0 +1,45 @@
+# Agent Note: 弃用对会话任意位置事件的同步读取
+
+Status: implemented
+
+[English](2026-09-09-deprecate-synchronous-session-event-reads.md) | 中文
+
+## 问题
+
+同步访问任意事件位置，使消费方依赖完整会话事件序列在内存中随时可用。存储的演进方向是不再将完整序列保存在内存中。历史事件一旦需要存储 I/O，运行时若不继续保留历史或阻塞等待存储，就无法维持相同的同步读取保证。
+
+即使只读取一个旧事件，新增调用也会加深这种依赖。恢复后反复扫描历史，还会使普通领域逻辑依赖历史存储，而不是它真正需要的状态。
+
+## 决策
+
+弃用所有同步读取会话事件历史任意位置或区间的操作，包括 `Session.eventAt()`、`Session.snapshotEvents()` 和 `Session.ownEvents()`。现有逻辑可以暂不迁移，但禁止新增调用。同样禁止新增暴露相同同步历史访问能力的别名或包装层。
+
+这三个方法通过 `@deprecated` JSDoc 声明该规则。这是 API 使用决策；当前 Session 实现仍在内存中保留完整事件序列。
+
+### 恢复后需要的状态
+
+结合设计持久事件字段与会话投影，使每个领域都能重建其消费方所需的状态。在恢复期间还原这些状态，随后通过新提交的事件增量维护。恢复后，普通逻辑读取投影或处理当前收到的事件，而不是回头查找历史事件。同步读取已经维护好的投影状态，不需要任意访问事件日志。
+
+按需展示的历史内容采用显式异步分页和渐进式加载，每次读取限制在请求的窗口内。在同步辅助方法背后加载完整序列，仍保留了本决策要消除的依赖。
+
+### 确实需要完整历史的操作
+
+fork 等少数操作可能确实需要完整历史序列或继承前缀。它们对这些记录的需求仍然成立，需要通过显式存储读取来满足。这不要求完整序列常驻内存，也不构成新增已弃用同步读取调用的例外。每个此类消费方都必须说明，为什么其结果需要完整序列，而不能只使用投影状态或局部历史窗口。
+
+## 曾考虑的替代方案
+
+**只弃用完整快照，保留同步单事件读取。** 单个被请求的事件也可能不在内存中。限制返回结果大小并不能消除存储依赖，`ownEvents()` 等辅助方法对后缀序列也保留着相同假设。
+
+**为保留读取 API 而让完整序列常驻内存。** 这会让消费方的便利性决定会话的内存保留方式，阻碍预期的存储设计。投影保留所需状态，显式历史读取则保留对记录本身的访问能力。
+
+**要求立即迁移所有现有调用方。** 本决策允许现有逻辑推迟迁移。禁止新增依赖可以限制剩余工作规模，无需将每个现有消费方都纳入同一次修改。
+
+## 后果
+
+新增领域行为必须使其事件数据与投影状态足以支持恢复后的执行。用户请求的历史仍可渐进式加载，确实需要完整历史的操作仍需设计存储读取路径。本决策不表示恢复或 fork 已经能够避免加载完整日志。
+
+当前 `typescript/no-deprecated` lint 规则会同时报告已有调用与新增调用。JSDoc 记录了暂缓迁移的约定，但 lint 尚不能区分允许保留的现有调用与禁止新增的调用。文档检查校验与源码一致的 API 声明及双语记录，并不强制执行这种区分。
+
+## 相关决策
+
+[会话不可变性决策](2026-06-11-dev-invariants-over-deep-readonly.zh.md)继续负责事件所有权与冻结；本决策取代其中对同步历史读取方法的使用建议。[投影读取必需性决策](2026-08-19-session-projection-mandatory-seam.zh.md)继续负责缺失状态时的失败规则与类型化状态读取。[可回溯压缩提案](../../proposed/feature/2026-07-06-recallable-compaction.zh.md)保留其回溯设计，并将其中拟议的同步历史访问替换为分页读取。

.agents/notes/proposed/feature/2026-07-06-recallable-compaction.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 .agents/notes/proposed/feature/2026-07-06-recallable-compaction.md
-2026-07-06-recallable-compaction.md: f0cf1b0602ad7dd5ae719fdd1e3b569b0bf5b448
-2026-07-06-recallable-compaction.zh.md: 8e8793f28be848e6231e86a3eaba099e68d9947e
+2026-07-06-recallable-compaction.md: 07b89116b72a1c1aac2d79ee5aa41ff6e5d02a4c
+2026-07-06-recallable-compaction.zh.md: 7347cb08c94665a6e5bb88655ec08d04921d08eb

.agents/notes/proposed/feature/2026-07-06-recallable-compaction.md

@@ -46,7 +46,7 @@ A new package `@deepseek-ai/dsh-tool-recall` (consumer-only, over the `dsh-sessi
 - `history_read(checkpoint, offset?)` — renders the shadowed span of any checkpoint in the log, including superseded ones, as `User:`/`Assistant:`/`Tool result:` transcript, paginated by a configured budget with a continuation cursor.
 - `history_search(query, checkpoint?, limit?)` — case-insensitive literal scan over every shadowed span; returns snippets with checkpoint ids and coverage metadata (`scanned`/`matched`/`truncated`). The zero-match hint notes the scan is literal and points at direct `history_read` of a plausible checkpoint.
 
-Both read `exec.agent.session.snapshotEvents()` (the tool-todo access pattern; non-agent callers rejected), render only surface-type message events, and return ordinary `tool/result`s — recalled bytes land at the context tail, logged, so reconstructability holds with no special casing. There is no new storage and no sidecar index: the session log stores the content, `compaction/summary.shadowedRange` and `shadowedSeqs` identify what each checkpoint replaced, and the tools read both. The tool schemas and the package's one system-prompt section are static strings; checkpoint ids reach the model only through footers. The transcript renderer moves from `compaction-basic` into `dsh-session`, shared by summarizer and tools.
+Both use explicit asynchronous, paged history reads under the [synchronous event-read deprecation](../../implemented/architecture/2026-09-09-deprecate-synchronous-session-event-reads.md) (non-agent callers rejected), render only surface-type message events, and return ordinary `tool/result`s — recalled bytes land at the context tail, logged, so reconstructability holds with no special casing. There is no new storage and no sidecar index: the session log stores the content, `compaction/summary.shadowedRange` and `shadowedSeqs` identify what each checkpoint replaced, and the tools read both. The tool schemas and the package's one system-prompt section are static strings; checkpoint ids reach the model only through footers. The transcript renderer moves from `compaction-basic` into `dsh-session`, shared by summarizer and tools.
 
 ### Cache and cost
 
@@ -86,7 +86,7 @@ Deferred until observation calls for them:
 - **One summarize call emitting all outputs** — rejected: the summarize path has no structured-output enforcement; parsing one free-text response apart is the fragile boundary the fail-closed design avoids.
 - **Model-chosen chunk boundaries** — deferred: parse-and-validate cost against unproven value; chunk policy sits behind config.
 - **Model-authored pointers** — rejected: pointers must be exact; deterministic assembly is.
-- **FTS/vector index sidecar** — rejected in-session: the live log is in memory and bounded, a literal scan under budget suffices; an index earns its keep at cross-session scope.
+- **FTS/vector index sidecar** — the rejection based on a resident, bounded live log is superseded by the [event-read policy](../../implemented/architecture/2026-09-09-deprecate-synchronous-session-event-reads.md). Reassess the index choice against paged historical reads before implementing recall.
 - **Semantic search fallback / secondary-model extraction in the recall path** — rejected: an LLM or embedding call there breaks keyless replay determinism; recall stays a pure function of the log.
 - **Raw events instead of rendered transcript** — rejected: leaks log-only vocabulary and chunk noise; the model reads what a model once saw.
 - **Doing nothing (resume/fork as recovery)** — rejected: it makes recovery a human act.

.agents/notes/proposed/feature/2026-07-06-recallable-compaction.zh.md

@@ -46,7 +46,7 @@ Status: proposed
 - `history_read(checkpoint, offset?)`：把日志中任意检查点（包括已被取代的检查点）遮蔽的区段渲染为 `User:`／`Assistant:`／`Tool result:` transcript（文本记录），并按配置预算分页，提供续传游标。
 - `history_search(query, checkpoint?, limit?)`：对每个被遮蔽区段进行不区分大小写的字面量扫描；返回带检查点 id 的片段与覆盖元数据（`scanned`／`matched`／`truncated`）。零匹配提示会说明扫描按字面量执行，并建议对可能的检查点直接使用 `history_read`。
 
-两个工具都读取 `exec.agent.session.snapshotEvents()`（沿用 tool-todo 访问模式；拒绝非 agent（智能体）调用方），只渲染表面类型的消息事件，并返回普通 `tool/result`：回溯字节会进入上下文尾部并记录到日志，因此无需特殊处理即可满足可重建性。系统不增加新存储或伴随索引：会话日志存储内容，`compaction/summary.shadowedRange` 和 `shadowedSeqs` 指明每个检查点替换了什么，这些工具读取两者。工具 schema 与该包唯一的系统提示词章节都是静态字符串；检查点 id 只会通过页脚抵达模型。transcript 渲染器从 `compaction-basic` 移入 `dsh-session`，供摘要器与工具共享。
+两个工具都按[同步事件读取弃用规则](../../implemented/architecture/2026-09-09-deprecate-synchronous-session-event-reads.zh.md)使用显式异步分页历史读取（拒绝非 agent（智能体）调用方），只渲染表面类型的消息事件，并返回普通 `tool/result`：回溯字节会进入上下文尾部并记录到日志，因此无需特殊处理即可满足可重建性。系统不增加新存储或伴随索引：会话日志存储内容，`compaction/summary.shadowedRange` 和 `shadowedSeqs` 指明每个检查点替换了什么，这些工具读取两者。工具 schema 与该包唯一的系统提示词章节都是静态字符串；检查点 id 只会通过页脚抵达模型。transcript 渲染器从 `compaction-basic` 移入 `dsh-session`，供摘要器与工具共享。
 
 ### 缓存与成本
 
@@ -86,7 +86,7 @@ Status: proposed
 - **一次摘要调用输出全部结果**：不予采纳，因为摘要路径没有结构化输出约束；解析一份自由文本响应并将其拆开，正是保守失败设计要避免的脆弱边界。
 - **由模型选择分片边界**：延后实现，因为相对于未经证明的收益，解析与校验成本过高；分片策略由配置控制。
 - **由模型编写指针**：不予采纳，因为指针必须精确，应由确定性代码组装。
-- **FTS／向量索引伴随存储**：在会话内不予采纳，因为实时日志已在内存中且大小有界，在预算内进行字面量扫描已经足够；只有跨会话范围才能证明索引的价值。
+- **FTS／向量索引伴随存储**：以实时日志常驻内存且大小有界为依据的否决，被[事件读取策略](../../implemented/architecture/2026-09-09-deprecate-synchronous-session-event-reads.zh.md)取代。实现回溯前，需要针对分页历史读取重新评估索引选择。
 - **回溯路径中的语义搜索回退／次级模型提取**：不予采纳，因为其中的 LLM 或嵌入调用会破坏无密钥回放的确定性；回溯必须保持为日志的纯函数。
 - **使用原始事件而不是渲染后的 transcript**：不予采纳，因为这会泄漏仅日志可见的词汇与分片噪声；模型应读取模型曾经看到的内容。
 - **什么都不做（用恢复／fork 补救）**：不予采纳，因为这会把恢复变成人工操作。

packages/core/session/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/core/session/README.md
-README.md: 402f3536402d78d0a70135290092cd7086706fb2
-README.zh.md: 303af9a878909f99e20dec1052b6592da7c8c415
+README.md: ebe4c1c29992b29b07ad38d7368ca5cef2253ee0
+README.zh.md: f5d0ac59f1276e4fe59c1cc449dcf6ce5a082aba

packages/core/session/README.md

@@ -55,7 +55,7 @@ Append, seed/restore, and event adoption/snapshot reject any `header.system` and
 
 ### Read the log
 
-`session.seq` reads the current log length without materializing an array, and `session.eventAt(seq)` reads one accepted, deeply frozen event by sequence number. `session.snapshotEvents(fromSeq?, toSeqExclusive?)` materializes a frozen, stable snapshot of a half-open range; a complete current snapshot is cached until the next append. `eventAt()`, `snapshotEvents()`, and `ownEvents()` are deprecated: existing logic may remain unmigrated for now, but new calls are prohibited. Callers that only need a length use `seq`.
+`session.seq` reads the current log length without materializing an array, and `session.eventAt(seq)` reads one accepted, deeply frozen event by sequence number. `session.snapshotEvents(fromSeq?, toSeqExclusive?)` materializes a frozen, stable snapshot of a half-open range; a complete current snapshot is cached until the next append. `eventAt()`, `snapshotEvents()`, and `ownEvents()` are deprecated: existing logic may remain unmigrated for now, but new calls are prohibited ([rationale](../../../.agents/notes/implemented/architecture/2026-09-09-deprecate-synchronous-session-event-reads.md)). Callers that only need a length use `seq`.
 
 Session log positions use two numeric types. `SessionSeq` identifies an existing event or inclusive event watermark; `SessionLogOffset` identifies a gap, prefix length, or read boundary and may equal the event count. `SessionSeqCursor` adds the `-1` “no event yet” value, while `OptionalSessionSeq` uses `null` when absence is data. The constructors validate non-negative safe integers, and the brands disappear at runtime, so durable JSON and wire values remain ordinary numbers.
 

packages/core/session/README.zh.md

@@ -55,7 +55,7 @@ session.deriveMessages()         // the derived model history
 
 ### 读取日志
 
-`session.seq` 无需物化数组即可读取当前日志长度，`session.eventAt(seq)` 按序列号读取单个已接受且深度冻结的事件。`session.snapshotEvents(fromSeq?, toSeqExclusive?)` 会物化半开区间的冻结稳定快照；当前完整快照会缓存到下一次追加。`eventAt()`、`snapshotEvents()` 和 `ownEvents()` 已弃用：现有逻辑可以暂不迁移，但禁止新增调用。只需要长度的调用方使用 `seq`。
+`session.seq` 无需物化数组即可读取当前日志长度，`session.eventAt(seq)` 按序列号读取单个已接受且深度冻结的事件。`session.snapshotEvents(fromSeq?, toSeqExclusive?)` 会物化半开区间的冻结稳定快照；当前完整快照会缓存到下一次追加。`eventAt()`、`snapshotEvents()` 和 `ownEvents()` 已弃用：现有逻辑可以暂不迁移，但禁止新增调用（[理由](../../../.agents/notes/implemented/architecture/2026-09-09-deprecate-synchronous-session-event-reads.zh.md)）。只需要长度的调用方使用 `seq`。
 
 会话日志位置使用两种数字类型。`SessionSeq` 标识已有事件或包含端点的事件水位；`SessionLogOffset` 标识间隙、前缀长度或读取边界，并且可以等于事件数量。`SessionSeqCursor` 添加 `-1` 这个“尚无事件”值，`OptionalSessionSeq` 则在缺失本身属于数据时使用 `null`。构造函数会校验非负安全整数，品牌在运行时会被擦除，因此持久 JSON 与 wire 值仍是普通数字。