round 2: pin checkpoint recognition at compile time

Move COMPACT_CHECKPOINT_SOURCE and isCompactCheckpointSource into a
cordis-free src/checkpoint.ts leaf, re-exported from the root so every
host-side consumer keeps its import. The client can then type-import the
leaf without reaching dsh-session's root, whose Context merge declares the
host sessions service and collides with the client's -- the dsh-commands/brand
shape. Renaming the plugin id now fails the client typecheck.

Also: keep recoverable summary text when a compact/summary mixes text with
other block types, and capture the seeded-history provenance seqs from the
pushes that produce them instead of deriving them by arithmetic.

packages/compact/compact/README.i18n.yaml

@@ -1,6 +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
-README.md: 17a5420ae9fa23ce4021b4d4927ae5b95962f979
-README.zh.md: d98251649cfdcf6b12e89a192a43b08b0f071f38
+#   pnpm run verify-translation-pairing --write packages/compact/compact/README.md
+README.md: b6386e8fed9c10cf072683fbdf78c85fb8ac8866
+README.zh.md: b59e03ccf846e88d328dfecdd76a2a490a966a0e

packages/compact/compact/README.md

@@ -59,6 +59,10 @@ The `compact/*` events extend `SessionEventMap` (merge-extensible) via declarati
 
 Subclass `CompactService`, implement `compactIfNeeded` and `compactRegion`, and load the subclass as a plugin — it registers as `ctx.compact`. Every successful backend uses `COMPACT_CHECKPOINT_SOURCE` on its replacement user message; `isCompactCheckpointSource()` recognizes the marker after persistence or cloning without depending on backend identity. A template- or model-backed implementation can live as a sibling package without changing callers or the shared token meter.
 
+## Recognizing a checkpoint outside the host program (`./checkpoint`)
+
+`COMPACT_CHECKPOINT_SOURCE` and `isCompactCheckpointSource()` are declared on the `@deepseek-ai/dsh-compact/checkpoint` subpath and re-exported from the root, so host-side consumers keep reading them from the root. The leaf imports no cordis and declares no module augmentation (the [`dsh-commands/brand`](../../ui/commands/README.md) shape), which is what lets a client or wire program name the checkpoint source: the package **root** cannot enter such a program at all, because it reaches `dsh-session`'s root and that `Context` merge declares the host `sessions` service against the client's own (`TS2717` — one program per side, per [development.md](../../../docs/development.md#typescript-project-layout)). The web client's transcript adapter pins its plugin literal to this leaf with a type-only import, so renaming the plugin id here is a compile error there.
+
 ## Model Experience
 
 ### Conversation history, when a backend is invoked

packages/compact/compact/README.zh.md

@@ -59,6 +59,10 @@
 
 继承 `CompactService`，实现 `compactIfNeeded` 与 `compactRegion`，再将子类作为插件加载：它会注册为 `ctx.compact`。每个成功后端都在替换 user 消息上使用 `COMPACT_CHECKPOINT_SOURCE`；`isCompactCheckpointSource()` 可在持久化或克隆后识别该标记，无需依赖后端身份。基于模板或模型的实现可以放在同级包中，不需更改调用方或共享 token meter。
 
+## 在 host 程序之外识别检查点（`./checkpoint`）
+
+`COMPACT_CHECKPOINT_SOURCE` 与 `isCompactCheckpointSource()` 声明在 `@deepseek-ai/dsh-compact/checkpoint` 子路径上，并由包根重新导出，因此 host 侧消费方仍从根读取它们。该叶子不导入 cordis、也不声明任何模块增强（即 [`dsh-commands/brand`](../../ui/commands/README.md) 的形状），这正是客户端或 wire 程序能够命名该检查点来源的原因：包的**根**根本无法进入这类程序，因为它会到达 `dsh-session` 的根，而那处 `Context` 合并会让 host 的 `sessions` 服务与客户端自己的冲突（`TS2717`——每侧一个程序，见 [development.md](../../../docs/development.md#typescript-project-layout)）。Web 客户端的对话记录适配器用仅类型导入把它的插件字面量钉在该叶子上，因此在此处改插件 id 会让那边编译失败。
+
 ## 模型体验
 
 ### 调用后端时的会话历史

packages/compact/compact/package.json

@@ -15,12 +15,17 @@
       "types": "./lib/types/invariant.d.ts",
       "default": "./lib/invariant.js"
     },
+    "./checkpoint": {
+      "types": "./lib/types/checkpoint.d.ts",
+      "default": "./lib/types/checkpoint.js"
+    },
     "./src/*": "./src/*",
     "./package.json": "./package.json"
   },
   "files": [
     "lib/index.js",
     "lib/invariant.js",
+    "lib/types/**/*.js",
     "lib/types/**/*.d.ts",
     "lib/types/**/*.d.ts.map",
     "src"

packages/compact/compact/src/checkpoint.ts

@@ -0,0 +1,27 @@
+/**
+ * The compaction seam's canonical checkpoint source: the plugin marker every
+ * backend stamps on the replacement user message that lands a checkpoint, plus
+ * the predicate that recognizes it.
+ *
+ * The seam itself lives in `@deepseek-ai/dsh-compact`, which re-exports both of
+ * these; this module is a pure value/predicate outlet (no cordis imports, no
+ * module augmentation) so client and wire programs can name the checkpoint
+ * source without loading the host plugin's Context merges — the
+ * `dsh-commands/brand` shape.
+ *
+ * @module @deepseek-ai/dsh-compact/checkpoint
+ */
+
+import type { MessageSource } from '@deepseek-ai/dsh-llm/message'
+
+/** Canonical source for the replacement user message produced by every compaction backend. */
+export const COMPACT_CHECKPOINT_SOURCE = Object.freeze({ kind: 'plugin', plugin: 'compact' } as const)
+
+/**
+ * Test whether a persisted message source identifies a compaction checkpoint.
+ * @param source - source restored from a surface user message.
+ * @returns whether the source carries the backend-independent checkpoint marker.
+ */
+export function isCompactCheckpointSource(source: MessageSource): boolean {
+  return source.kind === 'plugin' && source.plugin === COMPACT_CHECKPOINT_SOURCE.plugin
+}

packages/compact/compact/src/index.ts

@@ -8,24 +8,15 @@
  */
 
 import { Context, Service } from 'cordis'
-import type { MessageSource } from '@deepseek-ai/dsh-llm'
 import type { Session } from '@deepseek-ai/dsh-session'
 import type { CompactionResult } from './types.ts'
 
 export type { CompactionResult } from './types.ts'
 export { toolPairingBalancedAfter, toolPairingBalancedBefore } from './tool-pairing.ts'
-
-/** Canonical source for the replacement user message produced by every compaction backend. */
-export const COMPACT_CHECKPOINT_SOURCE = Object.freeze({ kind: 'plugin', plugin: 'compact' } as const)
-
-/**
- * Test whether a persisted message source identifies a compaction checkpoint.
- * @param source - source restored from a surface user message.
- * @returns whether the source carries the backend-independent checkpoint marker.
- */
-export function isCompactCheckpointSource(source: MessageSource): boolean {
-  return source.kind === 'plugin' && source.plugin === COMPACT_CHECKPOINT_SOURCE.plugin
-}
+// The checkpoint source and its predicate are declared on the cordis-free
+// `./checkpoint` leaf so client and wire programs can name them without this
+// root's Context merge; the root stays the host-side entry point for both.
+export { COMPACT_CHECKPOINT_SOURCE, isCompactCheckpointSource } from './checkpoint.ts'
 
 /** Why automatic policy is asking a backend to consider compaction. */
 export type CompactionTrigger = 'pressure' | 'context-overflow'