Merge pull request #2458 from deepseek-harness/xtr/fix-cold-session-list-metadata

fix(web): keep cold blank sessions out of recent lists

.agents/notes/implemented/bug-fix/2026-08-13-bounded-cold-blank-verification.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/bug-fix/2026-08-13-bounded-cold-blank-verification.md
+2026-08-13-bounded-cold-blank-verification.md: bf8d167d742001ce65b3e96713a9603adb19603e
+2026-08-13-bounded-cold-blank-verification.zh.md: 7cfef77a02308a8e75281877f8a774b41bb9559d

.agents/notes/implemented/bug-fix/2026-08-13-bounded-cold-blank-verification.md

@@ -0,0 +1,37 @@
+# Agent Note: Bound cold blank-session verification
+
+Status: implemented
+
+English | [中文](2026-08-13-bounded-cold-blank-verification.zh.md)
+
+## Problem
+
+The Web session tree hides blank Sessions and reuses the selected blank entry as New Session. Attached Sessions can derive blankness from their in-memory event log, but `session.list` normally avoids loading every cold log. Treating every materialized cold Session as non-blank exposes empty Sessions left by older versions. Treating a projection-cache `blank: true` as current can instead hide a real conversation after the log advances and the fail-soft cache remains stale.
+
+The same cold list used the JSONL artifact mtime for `updatedAt`. Opening a Session appends `session/end-seed`, so a pickup with no human prompt refreshed mtime and promoted that Session above recently used conversations.
+
+## Decision
+
+`dsh-host-apiproxy` registers `sessionListMetadata`, a projection containing `blank` and `lastPromptAt`. The attached summary folds the same functions directly over the live log. `blank` changes only from true to false on `turn/start`; `lastPromptAt` changes only on a `user/message` whose source kind is `user`.
+
+A cold summary trusts cached `blank: false`, because a checkpoint prefix containing `turn/start` remains non-blank. Cached `blank: true` and a cache miss do not prove the current log is blank. When persistence exposes a physical artifact through `locate()` and its observed size is at most the `coldBlankProbeMaxBytes` eligibility threshold (default 1 KiB per Session), the gateway calls `readFrom(id, 0)` and folds exact list metadata from the stored prefix. Files above the threshold, backends without a location, vanished artifacts, and failed reads all produce `blank: false`, keeping the Session visible.
+
+`updatedAt` is the later of `createdAt` and `lastPromptAt`. An eligible artifact read supplies exact `lastPromptAt` at no additional I/O cost; other cache misses or stale checkpoints order the Session too old rather than promoting it from an unrelated file write. After each asynchronous cold read, the gateway checks the live store again and replaces the cold result with an attached summary when another request resumed that Session meanwhile.
+
+## Alternatives considered
+
+**Trust cached `blank: true`.** Rejected because the projection cache deliberately permits a persisted log to advance beyond its checkpoint. A crash or fail-soft write failure after the first `turn/start` would hide a real conversation and could make the client reuse it as New Session.
+
+**Read every cold log.** Rejected because list latency and I/O would scale with total stored conversation bytes. The physical-size eligibility check targets small historical artifacts that can be checked cheaply and degrades larger unknowns toward visibility. It intentionally does not add a persistence operation solely to make the threshold atomic with the read: concurrent growth may increase one probe's read cost, but the additional events can only preserve visibility or change a blank result to non-blank.
+
+**Store blankness and recency in an authoritative persistence index.** Deferred because JSONL has an immutable first line and would require a second durable artifact with ordered updates, while SQLite would require a schema field. The broader exact-index design remains in the [last-activity proposal](../../proposed/architecture/2026-07-29-durable-last-activity-index.md).
+
+**Continue ordering JSONL by mtime.** Rejected because mtime records every artifact write, including pickup boundaries, rather than the latest human prompt. Its error direction promotes untouched Sessions to the front.
+
+## Consequences
+
+Existing small blank JSONL artifacts are hidden without depending on projection-cache availability, and a stale cache cannot hide a stored `turn/start`. A cold list may read each artifact whose observed physical size is within the configured threshold when its cache does not already prove non-blank. The default threshold compares compressed bytes for the shipped Zstandard JSONL backend.
+
+Blank artifacts above the threshold and blank Sessions on location-less backends remain visible. Missing or delayed recency cache entries for artifacts that are not read fall back to `createdAt`. These are conservative degradations: the UI may show an extra empty row or order a Session too low, but it does not hide a conversation or promote one because it was merely opened.
+
+The gateway-owned projection is an effect of the gateway fiber; unloading the gateway removes the key. Unit coverage pins exact-threshold eligibility, stale-true rejection, monotonic false reuse, exact small-log recency, live-attachment races, fallback direction, human-prompt recency, and fiber disposal. A keyless Web snapshot boots the shipped compressed JSONL composition, seeds a small cold blank artifact without a cache row, and verifies that the sidebar omits it.

.agents/notes/implemented/bug-fix/2026-08-13-bounded-cold-blank-verification.zh.md

@@ -0,0 +1,37 @@
+# Agent Note: 有界验证冷空白会话
+
+Status: implemented
+
+[English](2026-08-13-bounded-cold-blank-verification.md) | 中文
+
+## Problem
+
+Web 会话树会隐藏空白 Session，并把当前选中的空白项复用为 New Session。已附加 Session 可以从内存事件日志派生空白状态，但 `session.list` 通常不会加载每一份冷日志。把所有已物化的冷 Session 都视为非空，会暴露旧版本留下的空 Session；反过来，把 projection cache 中的 `blank: true` 当成当前事实，则可能在日志已经前进而 fail-soft cache 仍然陈旧时隐藏真实对话。
+
+同一份冷列表还曾用 JSONL 工件的 mtime 作为 `updatedAt`。打开 Session 会追加 `session/end-seed`，因此即使没有真人 prompt，单纯拾起也会刷新 mtime，并把该 Session 提升到最近使用的对话之前。
+
+## Decision
+
+`dsh-host-apiproxy` 注册 `sessionListMetadata` 投影，其中包含 `blank` 与 `lastPromptAt`。已附加摘要直接用同一组函数折叠实时日志。`blank` 只在 `turn/start` 时从 true 单调变为 false；`lastPromptAt` 只在来源 kind 为 `user` 的 `user/message` 上更新。
+
+冷摘要信任缓存的 `blank: false`，因为已包含 `turn/start` 的 checkpoint 前缀会始终保持非空。缓存的 `blank: true` 和 cache miss 都无法证明当前日志为空。当 persistence 通过 `locate()` 暴露物理工件，且其观测大小不超过 `coldBlankProbeMaxBytes` 资格阈值（默认每个 Session 1 KiB）时，网关调用 `readFrom(id, 0)`，从已存前缀折叠精确列表元数据。超过阈值的文件、不提供位置的后端、已消失的工件和读取失败都产生 `blank: false`，让 Session 保持可见。
+
+`updatedAt` 取 `createdAt` 与 `lastPromptAt` 中较晚者。符合资格的工件读取无需额外 I/O 即可提供精确 `lastPromptAt`；其他 cache miss 或陈旧 checkpoint 只会让 Session 排得偏旧，而不会因无关的文件写入被提升。每次异步冷读取后，网关都会再次检查实时 store；若另一请求期间已恢复该 Session，则用已附加摘要替换冷结果。
+
+## Alternatives considered
+
+**信任缓存的 `blank: true`。** 拒绝，因为 projection cache 有意允许持久日志前进到 checkpoint 之后。首个 `turn/start` 之后若发生崩溃或 fail-soft 写入失败，真实对话就会被隐藏，客户端还可能把它复用为 New Session。
+
+**读取每一份冷日志。** 拒绝，因为列表延迟与 I/O 会随所有已存对话的总字节数增长。物理大小资格检查只针对能够低成本核验的小型历史工件，更大的未知项则向保持可见降级。该检查有意不为“让阈值与读取原子化”单独新增 persistence 操作：并发增长可能增加一次探测的读取成本，但新增事件只会保持可见，或把空白结果改为非空。
+
+**把空白状态与最近时间存入权威 persistence index。** 暂缓，因为 JSONL 的首行不可变，需要增加带有顺序写入要求的第二份持久工件；SQLite 则需要 schema 字段。更广泛的精确索引设计仍由[最后活动提案](../../proposed/architecture/2026-07-29-durable-last-activity-index.md)负责。
+
+**继续按 mtime 排序 JSONL。** 拒绝，因为 mtime 记录包括拾起边界在内的每一次工件写入，而非最近真人 prompt；其错误方向会把未经操作的 Session 提升到列表开头。
+
+## Consequences
+
+既有的小型空白 JSONL 工件无需依赖 projection cache 是否存在即可被隐藏，陈旧 cache 也无法隐藏已存的 `turn/start`。对于 cache 尚不能证明非空，且观测物理大小在配置阈值内的每个 Session，冷列表可能读取其工件。对默认交付的 Zstandard JSONL 后端，该阈值比较压缩后的字节数。
+
+超过阈值的空白工件，以及来自不提供位置的后端的空白 Session 会保持可见。对于未被读取的工件，缺失或延迟的最近时间 cache 会回退到 `createdAt`。这些都是保守降级：UI 可能多显示一条空记录，或把 Session 排得偏低，但不会隐藏真实对话，也不会因为单纯打开而把会话提升到前面。
+
+网关自有投影是网关 fiber 的 effect；卸载网关会移除该 key。单元覆盖固定了临界大小资格、拒绝陈旧 true、复用单调 false、小日志精确最近时间、实时附加竞态、回退方向、真人 prompt 最近时间和 fiber 销毁。无密钥 Web snapshot 会启动发行版的压缩 JSONL 组合，在没有 cache row 的情况下播种一份小型冷空白工件，并验证侧栏不展示它。

.agents/notes/proposed/architecture/2026-07-29-durable-last-activity-index.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/architecture/2026-07-29-durable-last-activity-index.md
-2026-07-29-durable-last-activity-index.md: 0e441f54a719b29a1a450c133e08cdf7d2c82e9e
-2026-07-29-durable-last-activity-index.zh.md: ebc2e2167d7743eafc5a4600fe9a0f687349e1a3
+2026-07-29-durable-last-activity-index.md: 99e50dd40b789db5d896cb7f9e25fa8893b02ae2
+2026-07-29-durable-last-activity-index.zh.md: e317fb192d53353295e6b52f631707ba6b400b66

.agents/notes/proposed/architecture/2026-07-29-durable-last-activity-index.md

@@ -6,17 +6,17 @@ English | [中文](2026-07-29-durable-last-activity-index.zh.md)
 
 ## Problem
 
-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.
+A cold (persisted, unattached) session has no authoritative stored answer to "when did the user last prompt here". `dsh-host-apiproxy` serves `updatedAt` from the optional projection cache's `lastPromptAt`, falling back to `createdAt`, and the Web client sorts its Session tree by that value. The cache is fail-soft and checkpointed asynchronously, so a missing or delayed row makes a recently prompted Session sort too old.
 
-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. `dsh-host-apiproxy` keeps `session.history` inspection-only, but any Agent-bound ordinary-session control resumes through `agentFor()` and is enough to promote the cold artifact.
+The gateway previously used JSONL artifact mtime when available. mtime answers a different question: when the artifact was last written. Every durable write refreshes it, including a truncate-repair of a torn tail, synthetic closers that balance an interrupted turn, and the [`session/end-seed` boundary](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md) appended during pickup. That approximation promoted a Session merely because it was opened. The [bounded cold blank verification](../../implemented/bug-fix/2026-08-13-bounded-cold-blank-verification.md) removed mtime ordering and accepted the cache's conservative "too old" failure direction as an interim tradeoff.
 
-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.
+An attached summary can fold the live event log and select the latest human-authored `user/message`, but the cold path deliberately does not read large logs. Reading every log to compute `updatedAt` would make `list()` scale with total conversation bytes rather than Session count. The 1 KiB cold read used for metadata verification makes eligible small-artifact recency exact, but it does not make large-log ordering exact.
 
-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.
+Making cold ordering exact remains a durable-format decision, which is why it is scoped here rather than in the gateway workaround.
 
 ## Proposal
 
-Store last-activity time where a listing already reads — the session index — so `summarizeCold()` can serve it without opening the log. The coordinator computes the value, because it sees every append and already owns per-id state; backends persist it. That makes it a new `PersistenceBackend` contract element rather than backend-local bookkeeping, and keeps one definition of "activity" shared with the in-log `lastActivityTime()`.
+Store the latest human-prompt time where a listing already reads — the Session index — so `summarizeCold()` can serve it without opening the log or depending on a cache checkpoint. The coordinator computes the value because it sees every append and already owns per-id state; backends persist it. That makes it a new `PersistenceBackend` contract element rather than backend-local bookkeeping, with the same event predicate as the attached projection: `user/message` whose `source.kind` is `user`.
 
 The two shipped backends have opposite constraints, and the proposal is deliberately asymmetric about them:
 
@@ -25,7 +25,7 @@ The two shipped backends have opposite constraints, and the proposal is delibera
 
 Three questions must be answered before implementation, and none of them is settled here:
 
-**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.
+**How is the shared predicate owned?** A stored field encodes the rule at write time, where the writer sees one batch, while the attached summary folds a whole log. Both must use one exported event predicate or reducer so new message-source variants cannot make attached and cold ordering disagree.
 
 **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.
 
@@ -39,28 +39,29 @@ Three questions must be answered before implementation, and none of them is sett
 
 **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.
 
-**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.
+**Derive activity from a projection cache.** This is the current interim implementation. `session-projection-cache` folds tails past a watermark without changing the persistence format, but it is optional and fail-soft. Its absence or checkpoint delay makes ordering depend on cache availability and freshness, so it cannot provide the authoritative value proposed here.
 
 ## Acceptance criteria
 
 - `SessionSummary.updatedAt` for a cold session equals the same value the attached projection reports for that session, verified by resuming, quitting without a turn, and asserting the order is unchanged across both paths.
 - A resumed-then-abandoned session does not sort above a session worked in afterwards, in the web session tree and the TUI resume picker, pinned by an assembled snapshot rather than unit tests alone.
-- The activity rule has one definition: a test proves the stored field and `lastActivityTime()` agree over a log containing boundaries, closers, and a plain turn.
+- The prompt-time rule has one definition: a test proves the stored field and attached fold agree over a log containing human prompts, injected user messages, boundaries, and closers.
 - Pre-field artifacts load and list without error under the chosen fallback, with the fallback's ordering consequence asserted.
 - SQLite's `SCHEMA_VERSION` bump rejects the old on-disk version per the repo's no-migration stance.
 
 ## Risks
 
-**Two definitions of activity drift.** The stored field is computed per batch, the projection over a whole log. A new event type classified one way at write time and the other at read time yields a session whose cold and attached orderings disagree — a bug that only appears after a restart, which is where it is hardest to notice.
+**Two definitions of prompt time drift.** The stored field is computed per batch, the projection over a whole log. A new message source classified one way at write time and the other at read time yields a Session whose cold and attached orderings disagree — a bug that only appears after restart.
 
 **A JSONL sidecar can disagree with its log.** A crash between the log append and the sidecar write leaves a stale value with no torn-tail marker to repair it. Every consumer would need to treat the sidecar as a hint, which is close to what mtime already is.
 
 **The fallback reorders existing sessions.** Whichever fallback is chosen, users with existing logs see their picker and tree reorder once on upgrade. `createdAt` makes that reordering large.
 
-**Cost may exceed the defect.** The defect is a misordering of abandoned sessions. If the honest answer for JSONL is "keep the approximation", this note's outcome may be documenting that decision rather than implementing a field — and that is an acceptable outcome.
+**Cost may exceed the defect.** The remaining defect is conservative misordering when projection metadata is missing or delayed. If the honest answer for JSONL is "keep the cache fallback", this note's outcome may be documenting that decision rather than implementing a field.
 
 ## Related
 
-- [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.
+- [Bounded cold blank verification](../../implemented/bug-fix/2026-08-13-bounded-cold-blank-verification.md) — removes mtime ordering, defines the interim projection-cache fallback, and limits direct cold reads to small-artifact metadata verification.
+- [The end-seed log boundary](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md) — one of the non-prompt writes that made mtime unsuitable.
 - [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.
 - [Shared persistence write coordinator](../../implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md) — the append path a stored field would hook into.

.agents/notes/proposed/architecture/2026-07-29-durable-last-activity-index.zh.md

@@ -6,17 +6,17 @@ Status: proposed
 
 ## 问题
 
-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。
+一个冷会话（已持久化、未附加）对「用户上次是什么时候在这里发出 prompt」没有权威的已存储答案。`dsh-host-apiproxy` 从可选 projection cache 的 `lastPromptAt` 提供 `updatedAt`，缺失时回退到 `createdAt`，Web 客户端按该值为 Session 树排序。cache 采用 fail-soft 并异步写入 checkpoint，因此缺失或延迟的记录会让最近收到 prompt 的 Session 排得过旧。
 
-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。`dsh-host-apiproxy` 让 `session.history` 保持只执行检查，但任何绑定到 Agent 的普通会话控件都会通过 `agentFor()` 恢复会话，足以把冷态产物排到前面。
+网关以前会在可用时采用 JSONL 产物的 mtime。mtime 回答的是另一件事：这份产物上次是什么时候被写入。每一次持久写入都会刷新它，包括对撕裂尾部的截断修复、平衡中断轮次的合成 closer，以及拾起时追加的 [`session/end-seed` 边界](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md)。这套近似会让 Session 仅仅因为被打开就提升排序。[有界冷空白验证](../../implemented/bug-fix/2026-08-13-bounded-cold-blank-verification.md)移除了 mtime 排序，并把 cache 保守的「过旧」错误方向作为现阶段取舍。
 
-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。
+已附加摘要可以折叠实时事件日志并选择最新的真人 `user/message`，但冷路径有意不读取大日志。为计算 `updatedAt` 而读取每一份日志，会让 `list()` 的开销随对话总字节数而非 Session 数量增长。用于 metadata 验证的 1 KiB 冷读取可以让符合条件的小产物得到精确的最近时间，但不能让大日志的排序精确。
 
-[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。
+让冷排序变得精确仍是一项持久格式决策，因此其范围留在本文，而不是网关 workaround 中。
 
 ## 提案
 
-把最后活动时间存到列举本就会读取的地方，也就是会话索引，这样 `summarizeCold()` 无需打开日志就能给出答案。该值由协调器计算，因为它看得到每一次追加，而且本就拥有每 id 状态；由后端负责持久化。这样它就成为 `PersistenceBackend` 约定中新增的一个要素，而不是各后端本地的账目，同时让「活动」只保留一个定义，与日志内的 `lastActivityTime()` 共用。
+把最新真人 prompt 时间存到列举本就会读取的 Session 索引，这样 `summarizeCold()` 无需打开日志或依赖 cache checkpoint 就能给出答案。该值由协调器计算，因为它看得到每一次追加，而且本就拥有每 id 状态；由后端负责持久化。这样它就成为 `PersistenceBackend` 约定中新增的一个要素，而不是各后端本地账目，并与已附加投影使用同一个事件谓词：`source.kind` 为 `user` 的 `user/message`。
 
 两个已交付的后端受到的约束正好相反，本提案对它们有意采取不对称的处理：
 
@@ -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
 
 实现之前必须回答三个问题，本文对它们都没有定论：
 
-**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。
+**共享谓词由谁拥有？** 已存储字段在写入时编码规则，写入方只看到一个批次，而已附加摘要折叠整份日志。两者必须使用同一个导出的事件谓词或 reducer，避免新的消息来源变体让已附加排序与冷排序发生分歧。
 
 **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。
 
@@ -39,28 +39,29 @@ mtime 回答的是另一个问题：这份产物上次是什么时候被写入
 
 **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。
 
-**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。
+**从投影缓存派生活动时间。** 这是当前的过渡实现。`session-projection-cache` 会折叠水位线之后的尾部，无需改变持久格式，但它是可选且 fail-soft 的。缺失或 checkpoint 延迟会让排序取决于 cache 是否存在以及是否新鲜，因此无法提供本文所提议的权威值。
 
 ## 验收标准
 
 - 冷会话的 `SessionSummary.updatedAt` 等于已附加会话的投影为同一个会话报告的那个值；验证方式是恢复、不跑轮次就退出，并断言两条路径上的顺序都没有变化。
 - 在 web 会话树和 TUI 恢复选择器中，一个恢复后即被弃置的会话不会排到此后工作过的会话之前；由一份组装后的快照钉住，而不是只靠单元测试。
-- 活动规则只有一个定义：一个测试证明，在一份同时包含边界、closer 和一个普通轮次的日志上，已存储字段与 `lastActivityTime()` 的结果一致。
+- prompt 时间规则只有一个定义：一个测试证明，在包含真人 prompt、注入式 user message、边界和 closer 的日志上，已存储字段与已附加折叠结果一致。
 - 在选定的回退方案下，该字段引入之前的产物能够无错误地加载和列举，并且该回退在排序上的后果有断言覆盖。
 - 按本仓库不做迁移的立场，SQLite 的 `SCHEMA_VERSION` 递增会拒绝旧的磁盘版本。
 
 ## 风险
 
-**「活动」的两个定义发生漂移。** 已存储字段按批次计算，而投影在整份日志上计算。一种新事件类型若在写入时按一种方式归类、在读取时按另一种方式归类，就会产生一个冷排序与已附加排序彼此矛盾的会话；这个缺陷只在重启之后才显现，而那正是最难被注意到的地方。
+**prompt 时间的两个定义发生漂移。** 已存储字段按批次计算，而投影在整份日志上计算。一种新消息来源若在写入时按一种方式归类、在读取时按另一种方式归类，就会产生冷排序与已附加排序彼此矛盾的 Session；该缺陷只会在重启后显现。
 
 **JSONL 的伴随文件可能与它的日志不一致。** 在日志追加与伴随文件写入之间发生崩溃，会留下一个陈旧的值，而且没有撕裂尾部标记可用来修复它。每个消费方都得把伴随文件当作一条提示来对待，而这与 mtime 今天的地位已经很接近了。
 
 **回退方案会让既有会话重新排序。** 无论选定哪种回退，持有既有日志的用户都会在升级时看到自己的选择器和会话树重新排一次序。选 `createdAt` 会让这次重排的幅度很大。
 
-**代价可能超过这个缺陷本身。** 该缺陷是被弃置会话的排序出错。如果对 JSONL 来说诚实的答案是「保留这套近似」，那么本文的结局可能是记录下这个决定，而不是实现一个字段，而这也是一个可以接受的结局。
+**代价可能超过这个缺陷本身。** 剩余缺陷是 projection metadata 缺失或延迟时的保守错序。如果对 JSONL 来说诚实的答案是「保留 cache 回退」，那么本文的结局可能是记录该决定，而不是实现一个字段。
 
 ## 相关
 
-- [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。
+- [有界冷空白验证](../../implemented/bug-fix/2026-08-13-bounded-cold-blank-verification.md)——移除 mtime 排序，定义 projection cache 的过渡回退，并把直接冷读取限制为小产物 metadata 验证。
+- [种子结束日志边界](../../implemented/architecture/2026-07-30-session-end-seed-log-boundary.md)——让 mtime 不适用的非 prompt 写入之一。
 - [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。
 - [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。