feat(session): bound persistence write batching

.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.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/2026-06-18-shared-persistence-write-coordinator.md
-2026-06-18-shared-persistence-write-coordinator.md: 66b73b60ceec9497f1f1226747b8cebd831eb426
-2026-06-18-shared-persistence-write-coordinator.zh.md: 424ce6ec7384e8af7b979a29f58c31379a1d1850
+2026-06-18-shared-persistence-write-coordinator.md: 12131ebf8380fb8ba816618f0cbaf72cb004623a
+2026-06-18-shared-persistence-write-coordinator.zh.md: a11926b602651d8a7dc641f61371e882685b508b

.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md

@@ -14,7 +14,7 @@ Extract a backend-agnostic `PersistenceCoordinator` into `dsh-session-persistenc
 
 Composition, not inheritance. The coordinator is a concrete class the backend holds, not a base class the backend extends. The Agent Note's risk — "a coordinator must not make unusual backends fight an inheritance hierarchy" — is avoided: a backend exposes only the hooks and cannot reach the coordinator's private orchestration state. A third-party backend MAY still implement the abstract service directly without the coordinator, including immutable logical inspection and the default preparation fallback through `load`.
 
-The coordinator holds one controller for each exact live `Session`; the controller combines initialization, pending events, and the shared flush promise. Each `session/event` starts an eager drain, and `session/flush` observes quiescence rather than initiating the ordinary write path. The [flush-controller simplification](../simplification/2026-07-23-collapse-persistence-flush-state.md) owns this lifecycle.
+The coordinator holds one lifecycle entry for each exact live `Session`: initialization plus a package-private write controller that owns pending events, a fixed batching deadline, the active write, failure retention, and the shared flush barrier. Each `session/event` enters that bounded write path, and `session/flush` bypasses the wait to observe quiescence. The [flush-controller simplification](../simplification/2026-07-23-collapse-persistence-flush-state.md) owns controller consolidation; the [bounded batching decision](2026-08-08-bounded-session-persistence-write-batching.md) owns scheduling cadence.
 
 The coordinator retires a session from `session/disposed`: it waits for the controller's initialization and current flush, serializes a final drain, and removes the controller and owned per-id state only after success. A failure leaves the controller discoverable for backend teardown to retry. Settled per-id chain tails remove themselves only when they are still current, so a completion cannot erase a newer operation for the same id. Backend teardown unregisters write-path listeners, flushes every remaining controller, awaits per-id operations, and then closes the backend.
 
@@ -35,7 +35,7 @@ The single design choice that keeps the seam clean: the crash-repair "where is t
 
 ## Testing
 
-The shared `runPersistenceContract` (public-API contract) runs for every backend and proves that `inspect` balances an interrupted logical view without changing storage or revisions before `prepare` or `load` commits recovery. `runCoordinatorContract` (`tests/coordinator-contract.ts`) covers adoption, HMR, collision, session and backend disposal drains, and crash-tail repair through an in-memory reference, JSONL, and SQLite. `persistence.spec.ts` and `preparations.spec.ts` cover preparation reuse and reservation, bounded prepared-state eviction, eager follow-up batches, live-controller cleanup, same-id chain-tail races, failed-drain retry, and close ordering. The per-backend specs retain storage mechanics only. A through-coordinator torn-tail repair test per real backend keeps the opaque-marker branch covered because the contract crash case produces synthetic closers without a torn marker.
+The shared `runPersistenceContract` (public-API contract) runs for every backend and proves that `inspect` balances an interrupted logical view without changing storage or revisions before `prepare` or `load` commits recovery. `runCoordinatorContract` (`tests/coordinator-contract.ts`) covers adoption, HMR, collision, session and backend disposal drains, and crash-tail repair through an in-memory reference, JSONL, and SQLite. `persistence.spec.ts`, `preparations.spec.ts`, and `write-behind.spec.ts` cover preparation reuse and reservation, bounded prepared-state eviction, fixed-window follow-up batches, live-controller cleanup, same-id chain-tail races, failed-batch retry, and close ordering. The per-backend specs retain storage mechanics only. A through-coordinator torn-tail repair test per real backend keeps the opaque-marker branch covered because the contract crash case produces synthetic closers without a torn marker.
 
 ## Alternatives considered
 
@@ -44,4 +44,4 @@ The shared `runPersistenceContract` (public-API contract) runs for every backend
 
 ## Consequences
 
-The coordinator adds one indirection, an opaque torn marker, detached session-retirement tasks, and bounded prepared Session state, but centralizes correctness-heavy orchestration previously duplicated by every backend. Session disposal remains an observe-only event, so the session owner does not await persistence retirement; the coordinator contains failures, preserves pending events in the live controller, and makes backend teardown the quiescence boundary. Its hook surface stays narrow: identity, adoption, collision checks, preparation, and immutable inspection reuse `loadStored`; materialization stays atomic inside `appendBatch`; and listing bypasses the coordinator. Read models use `inspect` rather than `load`, so observing a persisted open turn does not commit interruption closers; the [Session preparation decision](2026-08-05-session-preparation.md) owns reuse, reservation, and publication. New backends implement storage primitives rather than copy the eager write lifecycle.
+The coordinator adds one indirection, an opaque torn marker, detached session-retirement tasks, and bounded prepared Session state, but centralizes correctness-heavy orchestration previously duplicated by every backend. Session disposal remains an observe-only event, so the session owner does not await persistence retirement; the coordinator contains failures, preserves pending events in the live controller, and makes backend teardown the quiescence boundary. Its hook surface stays narrow: identity, adoption, collision checks, preparation, and immutable inspection reuse `loadStored`; materialization stays atomic inside `appendBatch`; and listing bypasses the coordinator. Read models use `inspect` rather than `load`, so observing a persisted open turn does not commit interruption closers; the [Session preparation decision](2026-08-05-session-preparation.md) owns reuse, reservation, and publication. New backends implement storage primitives rather than copy the bounded write lifecycle.

.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.zh.md

@@ -14,7 +14,7 @@ Status: implemented
 
 组合，而非继承。协调器是后端持有的具体类，不是后端继承的基类。本 Agent Note 的风险——「协调器不得让非常规后端与继承层级作斗争」——由此规避：后端只暴露钩子，无法触及协调器的私有编排状态。第三方后端仍然可以完全不使用协调器、直接实现抽象服务，包括不可变逻辑检查，以及通过 `load` 实现的默认准备回退。
 
-协调器为每个存活的 `Session` 实例持有一个控制器；该控制器统合初始化、待处理事件与共享 flush promise。每个 `session/event` 都会立即启动排空，而 `session/flush` 只观察完全停稳，不会发起常规写入路径。[flush 控制器简化](../simplification/2026-07-23-collapse-persistence-flush-state.md)定义该生命周期。
+协调器为每个存活的 `Session` 实例持有一个生命周期条目：初始化，加上一个包私有写入控制器，后者负责待处理事件、固定批处理截止时间、活跃写入、失败保留和共享 flush 屏障。每个 `session/event` 都进入这条有界写入路径，`session/flush` 则绕过等待以观察完全停稳。控制器归并由 [flush 控制器简化](../simplification/2026-07-23-collapse-persistence-flush-state.md)定义；调度节奏由[有界批处理决策](2026-08-08-bounded-session-persistence-write-batching.md)定义。
 
 协调器通过 `session/disposed` 退役会话：它等待控制器完成初始化和当前 flush，串行执行最后一次排空，且仅在成功后才移除控制器与其拥有的每 id 状态。失败时保持控制器可被找到，以供后端 teardown（拆除）重试。每个 id 的已结算链尾仅在其仍是当前链尾时才移除自身，因此旧操作完成后不会抹除同一 id 的新操作。后端 teardown 会注销写入路径监听器、flush 每个剩余的控制器、等待所有按 id 串行化的操作，最后关闭后端。
 
@@ -35,7 +35,7 @@ Status: implemented
 
 ## 测试
 
-共享的 `runPersistenceContract`（公开 API 契约）为每个后端运行，并证明 `inspect` 会配平被中断的逻辑视图但不改变存储或修订版本，随后由 `prepare` 或 `load` 提交恢复。`runCoordinatorContract`（`tests/coordinator-contract.ts`）通过内存参考实现、JSONL 与 SQLite 覆盖接管、HMR、碰撞、会话与后端 dispose 排空和崩溃尾部修复。`persistence.spec.ts` 与 `preparations.spec.ts` 覆盖准备复用与预留、有界准备状态淘汰、立即执行的后续批次、存活控制器清理、同 id 链尾竞态、排空失败重试与关闭顺序。各后端自身的测试规格只保留存储机制。每个真实后端都有一个经由协调器的崩溃尾部修复测试，以覆盖不透明 marker 分支，因为契约中的崩溃用例会产生合成 closers，却不会产生 torn marker。
+共享的 `runPersistenceContract`（公开 API 契约）为每个后端运行，并证明 `inspect` 会配平被中断的逻辑视图但不改变存储或修订版本，随后由 `prepare` 或 `load` 提交恢复。`runCoordinatorContract`（`tests/coordinator-contract.ts`）通过内存参考实现、JSONL 与 SQLite 覆盖接管、HMR、碰撞、会话与后端 dispose 排空和崩溃尾部修复。`persistence.spec.ts`、`preparations.spec.ts` 与 `write-behind.spec.ts` 覆盖准备复用与预留、有界准备状态淘汰、固定窗口后续批次、存活控制器清理、同 id 链尾竞态、失败批次重试与关闭顺序。各后端自身的测试规格只保留存储机制。每个真实后端都有一个经由协调器的崩溃尾部修复测试，以覆盖不透明 marker 分支，因为契约中的崩溃用例会产生合成 closers，却不会产生 torn marker。
 
 ## 曾考虑的替代方案
 
@@ -44,4 +44,4 @@ Status: implemented
 
 ## 后果
 
-协调器增加了一层间接、一个不透明的 torn marker、脱离会话生命周期的退役任务，以及有界的已准备 Session 状态，但将此前每个后端重复的、对正确性要求很高的编排逻辑集中到一处。会话 dispose 仍是仅观察事件，因此会话所有者不会等待持久化退役；协调器会收容失败、在存活控制器中保留待处理事件，并以后端 teardown 为完全停稳边界。其钩子面保持窄小：标识校验、接管、碰撞检查、准备与不可变检查共用 `loadStored`；物化保持在 `appendBatch` 内原子完成；列举绕过协调器。读模型使用 `inspect` 而非 `load`，因此观察已持久化但仍开放的轮次时不会提交中断 closers；复用、预留与发布由 [Session 准备阶段决策](2026-08-05-session-preparation.md)定义。新后端只需实现存储原语，而无需复制立即写入生命周期。
+协调器增加了一层间接、一个不透明的 torn marker、脱离会话生命周期的退役任务，以及有界的已准备 Session 状态，但将此前每个后端重复的、对正确性要求很高的编排逻辑集中到一处。会话 dispose 仍是仅观察事件，因此会话所有者不会等待持久化退役；协调器会收容失败、在存活控制器中保留待处理事件，并以后端 teardown 为完全停稳边界。其钩子面保持窄小：标识校验、接管、碰撞检查、准备与不可变检查共用 `loadStored`；物化保持在 `appendBatch` 内原子完成；列举绕过协调器。读模型使用 `inspect` 而非 `load`，因此观察已持久化但仍开放的轮次时不会提交中断 closers；复用、预留与发布由 [Session 准备阶段决策](2026-08-05-session-preparation.md)定义。新后端只需实现存储原语，而无需复制有界写入生命周期。

.agents/notes/implemented/architecture/2026-08-08-bounded-session-persistence-write-batching.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/2026-08-08-bounded-session-persistence-write-batching.md
+2026-08-08-bounded-session-persistence-write-batching.md: 46dc612492fa1bfa805f77f865f14b168f52776f
+2026-08-08-bounded-session-persistence-write-batching.zh.md: 4aafdd652aad87cfe74a449428cdbbf13312d260

.agents/notes/implemented/architecture/2026-08-08-bounded-session-persistence-write-batching.md

@@ -0,0 +1,59 @@
+# Agent Note: Bounded session persistence write batching
+
+Status: implemented
+
+English | [中文](2026-08-08-bounded-session-persistence-write-batching.zh.md)
+
+## Problem
+
+Streaming responses can emit many `assistant/chunk` events in a short interval. The persistence coordinator previously scheduled a backend append as soon as an idle queue received one event. Events arriving while that append was active shared a follow-up batch, but a fast backend could still produce many small durable appends. Each JSONL append creates and syncs a Zstandard frame or raw suffix, while each SQLite append opens and commits a transaction and increments the session revision.
+
+Dropping chunk events or replacing them with assembled messages would reduce logical storage, but it would also change the event log, replay, sequence numbers, timestamps, and provenance. The write-amplification problem does not require that larger semantic change.
+
+### Quantified baseline
+
+Repository fixtures make the logical volume concrete. Decoding the current packed rows in [`goal-multi-turn-actions`](../../../../apps/web/tests/snapshots/goal-multi-turn-actions/session.jsonl) yields 2,098 events: 2,017 chunks (96.1%). Their unpacked JSONL lines occupy 332,647 of 379,225 event bytes (87.7%), while chunk packing reduces the committed file to 89,176 bytes and 182 storage rows, including 23 packed chunk rows. [`permission-policy-context`](../../../../apps/web/tests/snapshots/permission-policy-context/session.jsonl) yields 813 events: 746 chunks (91.8%) and 118,935 of 184,821 unpacked event bytes (64.4%); its packed file is 84,917 bytes and 123 storage rows, including 14 packed rows. These are tracked deterministic fixtures, not a production workload distribution, but they demonstrate why deleting chunks would reduce logical volume and why the existing packed-row layout already removes much of their JSON envelope cost.
+
+SQLite stores one row per logical event, so those same logical logs would retain 2,098 and 813 event rows respectively; batching does not change those counts. JSONL writes one Zstandard frame and fsync per durable append batch, while SQLite performs one transaction and one session-revision increment per batch. Runtime files do not record former append boundaries, so fixture row counts cannot honestly be presented as fsync or transaction counts.
+
+The scheduling bound is deterministic. With an immediately resolving sink, the former immediate controller could issue one append for each event arriving after the previous append completed. A controller test admits 20 events 10 ms apart: the 200 ms fixed window hands all 20 to one append. This is a 20-to-1 reduction for that cadence, not a universal ratio. Sparse events, mandatory flushes, slow prior writes, and different arrival rates produce different batch sizes.
+
+## Decision
+
+The first-party JSONL and SQLite plugins expose `writeBatchMaxDelayMs`, a positive integer no greater than Node's timer limit. Its default is `200`. Each plugin resolves the value at load and passes it to `PersistenceCoordinator`; the coordinator remains the single owner of batching behavior.
+
+Each live Session receives a package-private `SessionWriteBehind`. When its pending queue changes from empty to non-empty, the controller starts one fixed window. Later events join that batch without resetting the deadline: this is bounded coalescing, not debounce. When the deadline expires, the controller hands the complete pending prefix to the existing per-id serialization and `appendBatch` path. At most one write for a Session is active. Events admitted during that write form a new pending prefix with their own fixed deadline; if that deadline expires before the active write completes, the new prefix starts immediately after it.
+
+`writeBatchMaxDelayMs` bounds only the controller's intentional batching wait. Event-loop scheduling, initialization, an earlier serialized operation, and backend I/O can delay durable completion, so the option is not a hard fsync or crash-loss SLA.
+
+`session/flush` cancels any remaining wait and becomes a shared quiescence barrier. It drains the active attempt and every event admitted while the barrier is running before it resolves. Session retirement and backend disposal use that same barrier, so lifecycle teardown never waits for the batching timer. The checkpoint policy continues to place mandatory barriers before model requests and top-level tool side effects.
+
+Every event remains durable in its original order and shape. The controller copies each event on admission; no `assistant/chunk`, `seq`, `time`, surface metadata, or storage record is removed or rewritten. JSONL can therefore encode more events in one append frame, and SQLite can insert more event rows in one transaction, without changing either on-disk format or schema version.
+
+A failed background append restores its complete batch before any newer pending events, reports the failure once, and pauses automatic retry. The next newly admitted event opens a fresh fixed window; an explicit flush, retirement, or disposal retries immediately and surfaces a repeated failure to its caller. This avoids a timer-driven failure loop while preserving the existing recoverable flush boundary.
+
+This decision supersedes only the immediate scheduling cadence in [Collapse live persistence into one flush controller](../simplification/2026-07-23-collapse-persistence-flush-state.md). That note remains authoritative for one controller per live Session, retained failed batches, per-id serialization, retirement, and quiescent disposal. The [shared persistence coordinator](2026-06-18-shared-persistence-write-coordinator.md) remains the owner of the backend hook boundary.
+
+## Alternatives considered
+
+**Do not persist streaming chunk events.** Rejected here: it changes the event-sourced authority and recovery semantics rather than only physical write cadence. The existing [assembled-message rejection](../../rejected/simplification/2026-06-20-assembled-assistant-messages-only.md) remains the guardrail until a no-information-loss replacement defines replay, fork, provenance, sequence, and crash behavior independently. The [packed-row decision](2026-07-26-packed-chunk-rows-by-default.md) remains the complementary JSONL storage-size optimization.
+
+**Write only at semantic checkpoints.** Rejected: it maximizes batching but makes the ordinary crash-loss window depend on a separately mounted policy. Bounded background writes preserve progress between checkpoints while mandatory flushes keep their stronger ordering contract.
+
+**Debounce from the latest event.** Rejected: a continuously streaming response could postpone its first write indefinitely. A fixed window from the first pending event provides a real upper bound on intentional coalescing wait.
+
+**Implement timers separately in JSONL and SQLite.** Rejected: scheduling, failure retention, flush races, and teardown are backend-neutral lifecycle concerns. Duplicating them would reopen the drift that `PersistenceCoordinator` removed.
+
+## Verification
+
+The controller tests use a fake clock to prove the fixed, non-resetting 200 ms window; immediate and shared flush barriers; events admitted during a barrier; an over-budget tail behind an active write; ordered failure retention; paused automatic retry; and explicit retry of an overlapping background failure. Coordinator tests run the controller through Session notifications, retirement, collision reclamation, and teardown. The JSONL and SQLite suites retain their storage-format, transaction, recovery, and shared persistence-contract coverage.
+
+## Consequences
+
+High-frequency event bursts normally produce fewer durable append operations while preserving the exact logical event count. The reduction depends on arrival rate and backend latency: a burst inside one 200 ms window becomes one batch, while mandatory flushes and sparse events can still produce small batches.
+
+This decision does not cap pending event count or bytes behind a slow backend, and it does not reduce SQLite rows or the decoded logical log. A demonstrated memory bound or logical-retention policy would require its own failure and replay contract rather than another hidden timer rule.
+
+An admitted event can remain only in memory during the configured window, and then while scheduling or backend work is outstanding. Deployments choose a smaller value for a narrower ordinary loss window or a larger value for stronger batching. Explicit durability boundaries remain unchanged and bypass the wait.
+
+The new deep module gives the timer, active write, pending prefix, retry pause, and barrier one owner. `PersistenceCoordinator` retains initialization and identity serialization; backends retain only durable storage primitives. Neither `SESSION_FORMAT_VERSION` nor SQLite `SCHEMA_VERSION` changes.

.agents/notes/implemented/architecture/2026-08-08-bounded-session-persistence-write-batching.zh.md

@@ -0,0 +1,59 @@
+# Agent Note: 为会话持久化写入批处理设定上界
+
+Status: implemented
+
+[English](2026-08-08-bounded-session-persistence-write-batching.md) | 中文
+
+## 问题
+
+流式响应可能会在短时间内发出大量 `assistant/chunk` 事件。此前，只要空闲队列收到一个事件，持久化协调器就会立即调度一次后端追加。该追加仍在进行时到达的事件会共用一个后续批次，但如果后端速度很快，仍可能产生大量小规模的持久化追加。每次 JSONL 追加都会创建并同步一个 Zstandard 帧或原始格式后缀，而每次 SQLite 追加都会打开并提交一个事务，同时递增会话修订版本。
+
+丢弃分片事件或用组装后的消息替代它们可以减少逻辑存储量，但也会改变事件日志、回放、序列号、时间戳和来源信息。写放大问题不要求采取这项语义变化更大的方案。
+
+### 量化基线
+
+仓库 fixture（测试前置数据）让逻辑数据量有了具体依据。对当前 [`goal-multi-turn-actions`](../../../../apps/web/tests/snapshots/goal-multi-turn-actions/session.jsonl) 中的打包行进行解码，可得到 2,098 个事件，其中 2,017 个是分片（96.1%）。这些分片解包后的 JSONL 行共 332,647 字节，占全部事件 379,225 字节的 87.7%；分片打包则把仓库中的已提交文件缩小到 89,176 字节和 182 个存储行，其中包括 23 个打包分片行。[`permission-policy-context`](../../../../apps/web/tests/snapshots/permission-policy-context/session.jsonl) 可得到 813 个事件，其中 746 个是分片（91.8%）；这些分片解包后的 JSONL 行共 118,935 字节，占全部事件 184,821 字节的 64.4%。其打包文件为 84,917 字节，共 123 个存储行，其中包括 14 个打包行。这些是纳入版本控制的确定性 fixture，不代表生产工作负载分布；但它们说明了删除分片为何会降低逻辑数据量，也说明现有打包行布局已经消除了大量 JSON 包装开销。
+
+SQLite 每个逻辑事件存储一行，因此同样的逻辑日志会分别保留 2,098 和 813 个事件行；批处理不会改变这些数量。JSONL 每个持久化追加批次会写入一个 Zstandard 帧并执行一次 fsync，SQLite 每个批次会执行一次事务并递增一次会话修订版本。运行时文件不记录原有追加边界，因此不能把 fixture 的存储行数当作 fsync 或事务次数。
+
+调度上界是确定的。当写入端会立即完成每次操作时，原来的即时控制器可能对每个在前一次追加完成后到达的事件分别发起一次追加。一个控制器测试以 10 ms 的间隔接纳 20 个事件：200 ms 固定窗口会把全部 20 个事件交给一次追加。对于这种到达节奏，追加次数从 20 次降至 1 次，但这不是普遍比例。稀疏事件、强制 flush、较慢的前序写入和不同到达速率都会产生不同的批次大小。
+
+## 决策
+
+第一方 JSONL 与 SQLite 插件公开 `writeBatchMaxDelayMs`，其值必须是一个不超过 Node 计时器上限的正整数，默认值为 `200`。每个插件都会在加载时解析该值，再传给 `PersistenceCoordinator`；批处理行为仍只由协调器负责。
+
+每个活跃的 Session 都有一个包私有 `SessionWriteBehind`。当其待处理队列从空变为非空时，控制器会启动一个固定窗口。后续事件加入该批次但不会重置截止时间：这属于有界合并，而不是防抖。截止时间到达后，控制器会把完整的待处理前缀交给现有的按 id 串行化机制，并沿 `appendBatch` 路径写入。同一 Session 同时最多有一个活跃写入。该写入期间接纳的事件会形成新的待处理前缀，并拥有自己的固定截止时间；如果该截止时间在活跃写入完成前到期，新前缀会在前一次写入完成后立即开始写入。
+
+`writeBatchMaxDelayMs` 只限制控制器为批处理而主动等待的时间。事件循环调度、初始化、此前的串行化操作和后端 I/O 都可能延后持久化完成时间，因此该选项并不对 fsync 完成时间或崩溃数据丢失提供硬性 SLA。
+
+`session/flush` 会取消剩余等待，并充当共享的完全停稳屏障。它会在完成前等待活跃写入尝试，并排空屏障运行期间接纳的每个事件。Session 退役与后端 dispose（资源释放）共用该屏障，因此生命周期 teardown 绝不会等待批处理计时器。检查点策略仍会在模型请求与顶层工具副作用之前设置强制屏障。
+
+每个事件仍会按原有顺序和形态持久化。控制器会在接纳时复制每个事件；任何 `assistant/chunk`、`seq`、`time`、surface 元数据或存储记录都不会被删除或重写。因此，JSONL 可以在一个追加帧中编码更多事件，SQLite 可以在一个事务中插入更多事件行，而无需改变任一种磁盘格式或 schema 版本。
+
+后台追加失败后，控制器会把完整批次恢复到所有较新的待处理事件之前，报告一次该失败，并暂停自动重试。随后新接纳的第一个事件会开启新的固定窗口；显式 flush、退役或 dispose 会立即重试，如果故障再次发生，则会向调用方暴露该故障。这可以避免计时器驱动的失败循环，同时保留现有可恢复的 flush 边界。
+
+本决策仅取代[将实时持久化归并到单个刷新控制器](../simplification/2026-07-23-collapse-persistence-flush-state.md)中的即时调度节奏。对于每个活跃 Session 使用一个控制器、保留失败批次、按 id 串行化、退役和完全停稳的 dispose，原 Agent Note 仍是权威记录。后端钩子边界仍由[共享持久化协调器](2026-06-18-shared-persistence-write-coordinator.md)定义。
+
+## 备选方案
+
+**不持久化流式分片事件。** 这里不采纳：这会改变事件日志作为真源的地位及恢复语义，而不只是改变物理写入节奏。在无信息损失的替代方案独立定义回放、fork、来源信息、序列和崩溃行为之前，现有的[拒绝仅保留组装消息的决策](../../rejected/simplification/2026-06-20-assembled-assistant-messages-only.md)仍是防护规则。[打包行决策](2026-07-26-packed-chunk-rows-by-default.md)仍是配套的 JSONL 存储体积优化。
+
+**仅在语义检查点写入。** 不采纳：此方案会最大化批处理，却让普通的崩溃丢失窗口取决于另行挂载的策略。有界后台写入会在检查点之间持久化进度，而强制 flush 继续提供更强的顺序契约。
+
+**按最新事件重置防抖窗口。** 不采纳：持续不断的流式响应可能无限期推迟首次写入。由第一个待处理事件启动的固定窗口，为主动合并等待提供了真正的上界。
+
+**分别在 JSONL 与 SQLite 中实现计时器。** 不采纳：调度、失败保留、flush 竞态和 teardown 都是后端无关的生命周期问题。重复实现这些机制会重新引入 `PersistenceCoordinator` 已消除的实现漂移。
+
+## 验证
+
+控制器测试使用假时钟证明固定且不会重置的 200 ms 窗口、即时且可共享的 flush 屏障、屏障运行期间接纳的事件、在活跃写入之后已超过窗口时限的尾部批次、有序保留失败批次、暂停自动重试，以及显式 flush 会重试与其重叠发生的后台失败。协调器测试会在 Session 通知、退役、冲突回收和 teardown 路径中验证该控制器。JSONL 与 SQLite 测试套件继续覆盖存储格式、事务、恢复和共享持久化契约。
+
+## 后果
+
+高频事件突发通常会减少持久化追加操作，同时保持逻辑事件数量完全不变。减少幅度取决于事件到达速率和后端延迟：位于同一 200 ms 窗口内的突发事件会成为一个批次，而强制 flush 与稀疏事件仍可能产生小批次。
+
+本决策不会限制因后端缓慢而积压的待处理事件数量或字节数，也不会减少 SQLite 行数或解码后的逻辑日志。若要建立经过验证的内存上界或逻辑保留策略，就必须为其另行定义失败与回放契约，而不是再引入一条隐式计时器规则。
+
+接纳后的事件在配置窗口内可能只存在于内存中，此后在等待调度或后端工作完成期间也可能如此。部署可以选择较小的值以缩短普通丢失窗口，也可以选择较大的值以加强批处理。显式持久性边界保持不变，并会绕过等待。
+
+新的 deep module 让计时器、活跃写入、待处理前缀、重试暂停和屏障由一个所有方统一负责。`PersistenceCoordinator` 继续负责初始化和按标识串行化；后端仍只负责持久存储原语。`SESSION_FORMAT_VERSION` 与 SQLite `SCHEMA_VERSION` 均不变。