refactor(session): rename the seed boundary to end-seed
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Hypatia May
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# side as of the last confirmed-consistent state. Both languages carry equal authority;
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# after editing either side, bring the other along and re-record with:
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# pnpm run verify-translation-pairing --write .agents/notes/proposed/architecture/2026-07-29-durable-last-activity-index.md
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2026-07-29-durable-last-activity-index.md: 2569ce8dcdef4ce85713e4c3905c3a170be00a98
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2026-07-29-durable-last-activity-index.zh.md: 64078982bb09b0f94c41d5424d195d371c1a263f
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2026-07-29-durable-last-activity-index.md: 0938e7ea2aa817818ed552fd8b702795840b547a
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2026-07-29-durable-last-activity-index.zh.md: 647bce817444c77ac3cd6f51385472fff745212f
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@@ -8,11 +8,11 @@ English | [中文](2026-07-29-durable-last-activity-index.zh.md)
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A cold (persisted, unattached) session has no stored answer to "when was this last worked in". `dsh-host-apiproxy`'s `summarizeCold()` therefore approximates it with the log file's mtime where one exists — `locate()` resolves a per-session artifact for JSONL and `undefined` for SQLite, whose cold sessions fall back to `createdAt` — and the web client sorts its session tree by the resulting `updatedAt`. The two backends are wrong in opposite directions: JSONL reads too new, SQLite too old.
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mtime answers a different question: when the artifact was last written. Every durable write refreshes it, including writes that are not activity — a truncate-repair of a torn tail, the synthetic closers that balance an interrupted turn, and the [`session/inherited` boundary](../../implemented/architecture/2026-07-30-session-inherited-log-boundary.md) a seeded session appends. (A `flush` with nothing pending is not among them: the coordinator returns without reaching the backend.) The visible consequence is stable and wrong in one direction: a session touched without being worked in promotes itself above sessions the user actually worked in afterwards, and each touch re-promotes it. "Touched" is broader than "resumed" — `dsh-host-apiproxy`'s `agentFor()` resumes a cold session on first touch, and `sessions.history` reaches it when the web client merely opens one, so ordinary browsing is enough.
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mtime answers a different question: when the artifact was last written. Every durable write refreshes it, including writes that are not activity — a truncate-repair of a torn tail, the synthetic closers that balance an interrupted turn, and the [`session/end-seed` boundary](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md) a seeded session appends. (A `flush` with nothing pending is not among them: the coordinator returns without reaching the backend.) The visible consequence is stable and wrong in one direction: a session touched without being worked in promotes itself above sessions the user actually worked in afterwards, and each touch re-promotes it. "Touched" is broader than "resumed" — `dsh-host-apiproxy`'s `agentFor()` resumes a cold session on first touch, and `sessions.history` reaches it when the web client merely opens one, so ordinary browsing is enough.
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The attached projection has a real fix — `lastActivityTime()` skips boundaries — but it needs the event log, and the cold path deliberately does not read one. Reading the log to compute `updatedAt` would defeat the header-only listing that keeps `list()` scaling with session count rather than log size.
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The [boundary change](../../implemented/architecture/2026-07-30-session-inherited-log-boundary.md) raised the frequency of this defect, because a pickup now writes where nothing was written before; `dsh-host-apiproxy`'s README records it under Known Limitations. It did not introduce the approximation, and removing the approximation is a durable-format decision, which is why it is scoped here rather than there.
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The [boundary change](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md) raised the frequency of this defect, because a pickup now writes where nothing was written before; `dsh-host-apiproxy`'s README records it under Known Limitations. It did not introduce the approximation, and removing the approximation is a durable-format decision, which is why it is scoped here rather than there.
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## Proposal
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@@ -25,7 +25,7 @@ The two shipped backends have opposite constraints, and the proposal is delibera
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Three questions must be answered before implementation, and none of them is settled here:
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**Which events count as activity?** `lastActivityTime()` answers this for the log by excluding `session/inherited`. A stored field encodes the rule at write time, where the writer sees one batch rather than the whole log. The two must not drift, or the attached and cold surfaces will disagree about the same session.
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**Which events count as activity?** `lastActivityTime()` answers this for the log by excluding `session/end-seed`. A stored field encodes the rule at write time, where the writer sees one batch rather than the whole log. The two must not drift, or the attached and cold surfaces will disagree about the same session.
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**How do pre-field logs behave?** Existing artifacts have no value. Falling back to mtime keeps them at today's accuracy; falling back to `createdAt` is honest but reorders every existing session in the picker and the tree.
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@@ -37,7 +37,7 @@ Three questions must be answered before implementation, and none of them is sett
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**Keep mtime and exclude boundary writes from it.** Rejected as impossible rather than undesirable: mtime is the filesystem's, not the backend's. Nothing short of restoring the timestamp after every boundary write would preserve it, and that races any concurrent reader and lies about the artifact.
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**Write the boundary only when repair occurred.** Would reduce the frequency, and the [boundary note](../../implemented/architecture/2026-07-30-session-inherited-log-boundary.md) already rejected it: the predicate must hold for an orderly restart too. Trading a correctness invariant for timestamp accuracy is the wrong direction.
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**Write the boundary only when repair occurred.** Would reduce the frequency, and the [boundary note](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md) already rejected it: the predicate must hold for an orderly restart too. Trading a correctness invariant for timestamp accuracy is the wrong direction.
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**Derive activity from a projection cache.** `session-projection-cache` already folds tails past a watermark, so a last-activity unit would ride existing machinery. Rejected as the primary shape because the cache is an optional composition entry; a listing served only when a cache plugin is mounted makes ordering depend on composition.
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@@ -61,6 +61,6 @@ Three questions must be answered before implementation, and none of them is sett
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## Related
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- [The inherited-history log boundary](../../implemented/architecture/2026-07-30-session-inherited-log-boundary.md) — one of the non-activity writes mtime counts; `dsh-session` owns `lastActivityTime()`, the in-log projection a stored field must agree with.
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- [The end-seed log boundary](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md) — one of the non-activity writes mtime counts; `dsh-session` owns `lastActivityTime()`, the in-log projection a stored field must agree with.
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- [Session persistence](../../implemented/architecture/2026-06-14-session-persistence.md) — the append-only and never-rewrite invariants that rule out a mutable JSONL header field.
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- [Shared persistence write coordinator](../../implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md) — the append path a stored field would hook into.
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@@ -8,11 +8,11 @@ Status: proposed
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一个冷会话（已持久化、未附加）对「上次是什么时候在这里面工作过」没有任何已存储的答案。因此 `dsh-host-apiproxy` 的 `summarizeCold()` 在存在日志文件时用它的 mtime 来近似它——`locate()` 为 JSONL 解析出一个逐会话产物，为 SQLite 解析出 `undefined`，而 SQLite 的冷会话会回退到 `createdAt`——而 web 客户端就按由此得到的 `updatedAt` 为自己的会话树排序。这两个后端错的方向正好相反：JSONL 读出来偏新，SQLite 偏旧。
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mtime 回答的是另一个问题：这份产物上次是什么时候被写入的。每一次持久写入都会刷新它，包括那些并不是活动的写入：一次对撕裂尾部的截断修复、用来平衡被中断的轮次的那些合成 closer，以及带种子的会话会追加的 [`session/inherited` 边界](../../implemented/architecture/2026-07-30-session-inherited-log-boundary.md)。（没有待处理内容的 `flush` 不在其中：协调器在到达后端之前就返回了。）用户可见的后果是稳定的，而且只朝一个方向错：一个被触碰过却没有在里面工作过的会话，会把自己排到用户此后真正工作过的那些会话之前，而且每次触碰都会重新把它排上去一次。「触碰」比「恢复」的范围更宽——`dsh-host-apiproxy` 的 `agentFor()` 会在首次触碰时恢复一个冷会话，而 web 客户端仅仅打开一个会话时 `sessions.history` 就会到达它，因此普通的浏览就够了。
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mtime 回答的是另一个问题：这份产物上次是什么时候被写入的。每一次持久写入都会刷新它，包括那些并不是活动的写入：一次对撕裂尾部的截断修复、用来平衡被中断的轮次的那些合成 closer，以及带种子的会话会追加的 [`session/end-seed` 边界](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md)。（没有待处理内容的 `flush` 不在其中：协调器在到达后端之前就返回了。）用户可见的后果是稳定的，而且只朝一个方向错：一个被触碰过却没有在里面工作过的会话，会把自己排到用户此后真正工作过的那些会话之前，而且每次触碰都会重新把它排上去一次。「触碰」比「恢复」的范围更宽——`dsh-host-apiproxy` 的 `agentFor()` 会在首次触碰时恢复一个冷会话，而 web 客户端仅仅打开一个会话时 `sessions.history` 就会到达它，因此普通的浏览就够了。
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已附加会话的那个投影有真正的修复办法（`lastActivityTime()` 会跳过边界），但它需要事件日志，而冷路径有意不去读日志。为计算 `updatedAt` 而读取日志，会让只读 header 的列举失去意义，而正是它让 `list()` 的开销随会话数量而非日志体量增长。
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[边界那次变更](../../implemented/architecture/2026-07-30-session-inherited-log-boundary.md)提高了这个缺陷的出现频率，因为一次拾起如今会在此前完全无写入的路径上产生写入；`dsh-host-apiproxy` 的 README 已在 Known Limitations 中记录该项。它并没有引入这套近似做法，而移除这套近似是一项持久格式决策，因此它的范围划在本文，而不是那里。
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[边界那次变更](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md)提高了这个缺陷的出现频率，因为一次拾起如今会在此前完全无写入的路径上产生写入；`dsh-host-apiproxy` 的 README 已在 Known Limitations 中记录该项。它并没有引入这套近似做法，而移除这套近似是一项持久格式决策，因此它的范围划在本文，而不是那里。
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## 提案
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@@ -25,7 +25,7 @@ mtime 回答的是另一个问题：这份产物上次是什么时候被写入
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实现之前必须回答三个问题，本文对它们都没有定论：
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**哪些事件算作活动？** 对日志而言，`lastActivityTime()` 通过排除 `session/inherited` 回答了这个问题。一个已存储字段是在写入时编码这条规则的，而写入方在那里只看到一个批次，不是整份日志。两者不得发生漂移，否则已附加表层与冷表层会对同一个会话给出彼此矛盾的答案。
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**哪些事件算作活动？** 对日志而言，`lastActivityTime()` 通过排除 `session/end-seed` 回答了这个问题。一个已存储字段是在写入时编码这条规则的，而写入方在那里只看到一个批次，不是整份日志。两者不得发生漂移，否则已附加表层与冷表层会对同一个会话给出彼此矛盾的答案。
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**该字段引入之前的日志表现如何？** 既有产物里没有这个值。回退到 mtime 能让它们保持今天的准确度；回退到 `createdAt` 是诚实的，但会把选择器和会话树里每一个既有会话都重新排一次序。
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@@ -37,7 +37,7 @@ mtime 回答的是另一个问题：这份产物上次是什么时候被写入
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**保留 mtime，但把边界的写入排除在它之外。** 否决的理由是做不到，而不是不合意：mtime 属于文件系统，不属于后端。除了在每次边界写入之后把时间戳复原，没有别的办法能保住它，而那样做会与任何并发读取方产生竞态，也会对这份产物撒谎。
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**仅在确实发生了修复时才写入边界。** 这能降低出现频率，而[边界 Agent Note](../../implemented/architecture/2026-07-30-session-inherited-log-boundary.md)已经否决过它：谓词对有序重启同样必须成立。用一条正确性不变式去换时间戳的准确度，方向是错的。
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**仅在确实发生了修复时才写入边界。** 这能降低出现频率，而[边界 Agent Note](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md)已经否决过它：谓词对有序重启同样必须成立。用一条正确性不变式去换时间戳的准确度，方向是错的。
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**从投影缓存派生活动时间。** `session-projection-cache` 本就会折叠水位线之后的尾部，因此一个最后活动单元可以搭乘既有机制。它作为主形态被否决，因为该缓存是一个可选的组合项；只有挂载了缓存插件才提供的列举，会让排序取决于如何组合。
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@@ -61,6 +61,6 @@ mtime 回答的是另一个问题：这份产物上次是什么时候被写入
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## 相关
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- [继承历史日志边界](../../implemented/architecture/2026-07-30-session-inherited-log-boundary.md)——mtime 会计入的非活动写入之一；`dsh-session` 拥有 `lastActivityTime()`，也就是一个已存储字段必须与之保持一致的那个日志内投影。
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- [种子结束日志边界](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md)——mtime 会计入的非活动写入之一；`dsh-session` 拥有 `lastActivityTime()`，也就是一个已存储字段必须与之保持一致的那个日志内投影。
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- [会话持久化](../../implemented/architecture/2026-06-14-session-persistence.md)——仅追加与绝不重写这两条不变式，正是它们排除了可变的 JSONL header 字段。
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- [共享持久化写入协调器](../../implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md)——一个已存储字段将挂入的那条追加路径。
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