fix(web): restrict message forks to completed turn tails

packages/client/runtime/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/client/runtime/README.md
-README.md: f956be22384a42e9ed30e8aa5f25fe8173cc9f9c
-README.zh.md: 49449c51d89d957b5bd39798c9167607f72a5c3a
+README.md: 91844016ce58e172161343022a1824be91b7ff2f
+README.zh.md: 0ea77774c6181858748a8adbc737de7e213be31b

packages/client/runtime/README.md

@@ -26,7 +26,7 @@ SlotsService gives the renderer separate bare observables for `useSessions` and
 
 ## The human transcript
 
-`ConversationSnapshot.nodes` is the human transcript, not the model surface. `TranscriptAdapter` projects the raw window in log order — every append-origin surface event (`isAppendSurfaceEvent`) at its own log position, plus one `CompactionSummaryNode` marker per landed compaction checkpoint — and never consults surface order. A landed compaction therefore keeps the conversation it shadowed on the model side: the marker reports where the model stopped seeing that history instead of erasing it. Model-only replacement copies stay out: a pruned `tool/result` and a regenerated `assistant/message` rewrite one node for the model and mark no boundary. A checkpoint is a `user/message` carrying the compaction seam's plugin source that **replaced** a surface range; an appending plugin-sourced `user/message` is injected context, not a compaction. The adapter's plugin literal is pinned to the seam's own declaration by a type-only import of the cordis-free [`dsh-compact/checkpoint`](../../compact/compact/README.md) leaf, so renaming it there fails `tsc` here; a **value** import of the package would fail the client purity gate, and the package **root** is unreachable even as a type (it reaches `dsh-session`'s root, whose `Context` merge collides the host `sessions` with this program's). `tests/compact-checkpoint-pin.spec.ts` covers the same drift behaviorally.
+`ConversationSnapshot.nodes` is the human transcript, not the model surface. `TranscriptAdapter` projects the raw window in log order — every append-origin surface event (`isAppendSurfaceEvent`) at its own log position, plus one `CompactionSummaryNode` marker per landed compaction checkpoint — and never consults surface order. `ConversationSnapshot.turnEnds` maps each completed turn in that window to its `turn/end` seq, retaining turn completion independently from the transcript so presentation can require a real boundary before exposing an action. A landed compaction therefore keeps the conversation it shadowed on the model side: the marker reports where the model stopped seeing that history instead of erasing it. Model-only replacement copies stay out: a pruned `tool/result` and a regenerated `assistant/message` rewrite one node for the model and mark no boundary. A checkpoint is a `user/message` carrying the compaction seam's plugin source that **replaced** a surface range; an appending plugin-sourced `user/message` is injected context, not a compaction. The adapter's plugin literal is pinned to the seam's own declaration by a type-only import of the cordis-free [`dsh-compact/checkpoint`](../../compact/compact/README.md) leaf, so renaming it there fails `tsc` here; a **value** import of the package would fail the client purity gate, and the package **root** is unreachable even as a type (it reaches `dsh-session`'s root, whose `Context` merge collides the host `sessions` with this program's). `tests/compact-checkpoint-pin.spec.ts` covers the same drift behaviorally.
 
 Because the projection is log-ordered, the node array is seq-monotonic by construction: log-only `command/run` / `command/done` nodes splice in by seq, `Session` merges interrupted frozen nodes by their fractional seqs, and a window whose checkpoint cites a shadowed range outside it renders the marker with nothing logged. The marker's summary text comes from the checkpoint's `compact/summary` provenance; a window cut that left the provenance outside makes the row non-expandable rather than empty, and a later page that supplies it resolves the text. Performance contract: one append materializes at most one node and copies the projection only when it adds that node; an event that changes no node keeps the previous array reference (a chunk storm costs nothing), and unchanged nodes keep their object identity.
 

packages/client/runtime/README.zh.md

@@ -26,7 +26,7 @@ SlotsService 分别为 renderer 提供 `useSessions` 与 `useWorkspaces` 的裸
 
 ## 面向人的 transcript（文本记录）
 
-`ConversationSnapshot.nodes` 是面向人的 transcript，不是模型 surface。`TranscriptAdapter` 按日志顺序投影原始窗口——每个 append 来源的 surface 事件（`isAppendSurfaceEvent`）落在它自己的日志位置上，外加每次落地的压缩（compaction）检查点贡献一个 `CompactionSummaryNode` 标记——且从不查询 surface 顺序。于是一次落地的压缩会保留它在模型侧遮蔽掉的对话：标记报告模型从哪里开始看不见那段历史，而不是把它抹掉。仅模型可见的 replacement 副本不进入记录：被裁剪的 `tool/result` 和重新生成的 `assistant/message` 只为模型重写一个节点，不标记任何边界。检查点是携带压缩 seam 插件来源、且**替换**了一段 surface 范围的 `user/message`；一条 append 的插件来源 `user/message` 是注入上下文，不是压缩。适配器的插件字面量通过对无 cordis 的 [`dsh-compact/checkpoint`](../../compact/compact/README.md) 叶子做仅类型导入，钉在压缩 seam 自己的声明上：在那里改名会让此处 `tsc` 失败；而对该包（package）做**值**导入会被客户端纯度门禁拒绝，包的**根**即便作为类型也无法到达（它会到达 `dsh-session` 的根，其 `Context` 合并会让 host 的 `sessions` 与本程序的冲突）。`tests/compact-checkpoint-pin.spec.ts` 从行为侧覆盖同一漂移。
+`ConversationSnapshot.nodes` 是面向人的 transcript，不是模型 surface。`TranscriptAdapter` 按日志顺序投影原始窗口——每个 append 来源的 surface 事件（`isAppendSurfaceEvent`）落在它自己的日志位置上，外加每次落地的压缩（compaction）检查点贡献一个 `CompactionSummaryNode` 标记——且从不查询 surface 顺序。`ConversationSnapshot.turnEnds` 把该窗口中的每个已完成轮次映射到其 `turn/end` seq；它独立于 transcript 保留轮次完成状态，使呈现层能够在暴露操作前要求存在真实边界。于是一次落地的压缩会保留它在模型侧遮蔽掉的对话：标记报告模型从哪里开始看不见那段历史，而不是把它抹掉。仅模型可见的 replacement 副本不进入记录：被裁剪的 `tool/result` 和重新生成的 `assistant/message` 只为模型重写一个节点，不标记任何边界。检查点是携带压缩 seam 插件来源、且**替换**了一段 surface 范围的 `user/message`；一条 append 的插件来源 `user/message` 是注入上下文，不是压缩。适配器的插件字面量通过对无 cordis 的 [`dsh-compact/checkpoint`](../../compact/compact/README.md) 叶子做仅类型导入，钉在压缩 seam 自己的声明上：在那里改名会让此处 `tsc` 失败；而对该包（package）做**值**导入会被客户端纯度门禁拒绝，包的**根**即便作为类型也无法到达（它会到达 `dsh-session` 的根，其 `Context` 合并会让 host 的 `sessions` 与本程序的冲突）。`tests/compact-checkpoint-pin.spec.ts` 从行为侧覆盖同一漂移。
 
 由于投影按日志顺序，节点数组天然按 seq 单调：仅日志的 `command/run` / `command/done` 节点按 seq 插入，`Session` 按分数 seq 归并被打断的冻结节点，而检查点所引范围落在窗口之外的窗口会渲染出标记且不打印任何日志。标记的摘要文本来自检查点的 `compact/summary` 溯源；窗口切分把溯源留在窗口外时该行不可展开而非空白，后续补上溯源的分页会解析出文本。性能契约：一次追加最多物化一个节点，并且仅在加入该节点时复制投影；不改变任何节点的事件保持上一次的数组引用（分片风暴零成本），未变化的节点保持其对象标识。
 

packages/client/runtime/src/client/sessions/conversation.ts

@@ -322,6 +322,8 @@ export interface ConversationSnapshot {
   sessionId: SessionId
   /** Human transcript plus retry notices and interrupted-turn terminal nodes in event order. */
   nodes: readonly ConversationNode[]
+  /** In-window completed turn number -> its `turn/end` event seq. */
+  turnEnds: ReadonlyMap<number, number>
   partial: PartialAssistant | null
   runningCalls: readonly RunningToolCall[]
   /**

packages/client/runtime/src/client/sessions/session.ts

@@ -113,6 +113,11 @@ export class Session implements SessionFace {
   private pendingCache: { rev: number; value: PendingInteraction[] } | null = null
   private derivedRev = 0
   private nodesCache: { projected: readonly ConversationNode[]; derivedRev: number; value: readonly ConversationNode[] } | null = null
+  /** Completed turn boundaries retained from the raw window so presentation
+   *  actions never infer a safe fork point from transcript content alone. */
+  private turnEnds = new Map<number, number>()
+  private turnEndsRev = 0
+  private turnEndsCache: { rev: number; value: ReadonlyMap<number, number> } | null = null
   /** Authoritative stream-only inbox snapshot; pending work never hits history. */
   private queued: QueuedMessage[] = []
   private queueRev = 0
@@ -807,6 +812,8 @@ export class Session implements SessionFace {
         return
       }
       case 'turn/end': {
+        this.turnEnds.set(event.data.turn, event.seq)
+        this.turnEndsRev++
         if (event.data.reason.kind === 'aborted' || event.data.reason.kind === 'disposed') {
           this.settleScheduledRetry('cancelled', event.data.turn)
         }
@@ -897,6 +904,8 @@ export class Session implements SessionFace {
     this.callsRev++
     this.derivedNodes = []
     this.derivedRev++
+    this.turnEnds = new Map()
+    this.turnEndsRev++
     this.codeDispatches = new Map()
     this.dispatchesRev++
     for (let i = 0; i < this.events.length; i++) {
@@ -928,6 +937,9 @@ export class Session implements SessionFace {
     if (this.callsCache === null || this.callsCache.rev !== this.callsRev) {
       this.callsCache = { rev: this.callsRev, value: [...this.openCalls.values()] }
     }
+    if (this.turnEndsCache === null || this.turnEndsCache.rev !== this.turnEndsRev) {
+      this.turnEndsCache = { rev: this.turnEndsRev, value: new Map(this.turnEnds) }
+    }
     if (this.pendingCache === null || this.pendingCache.rev !== this.pendingRev) {
       this.pendingCache = { rev: this.pendingRev, value: [...this.pending.values()] }
     }
@@ -941,6 +953,7 @@ export class Session implements SessionFace {
     return {
       sessionId: this.sessionId,
       nodes,
+      turnEnds: this.turnEndsCache.value,
       partial,
       runningCalls: this.callsCache.value,
       pending: this.pendingCache.value,

packages/client/runtime/tests/session.spec.ts

@@ -426,6 +426,7 @@ describe('live event path', () => {
     feed(ev.turnEnd(10, 1, 'aborted')) // no assistant/message ever arrives
     const snapshot = session.getSnapshot()
     expect(snapshot.partial).toBeNull()
+    expect(snapshot.turnEnds.get(1)).toBe(10)
     const frozen = snapshot.nodes.at(-1)
     expect(frozen).toMatchObject({ kind: 'assistant', interrupted: true, blocks: [{ kind: 'text', text: '说到一半' }] })
     // Ordered inside the flow: after the user message (seq 7), before any later turn.
@@ -1215,6 +1216,7 @@ describe('reference stability (the memo contract)', () => {
     expect(after).not.toBe(before)
     expect(after.runningCalls).toBe(before.runningCalls)
     expect(after.pending).toBe(before.pending)
+    expect(after.turnEnds).toBe(before.turnEnds)
     // And a mutation on the tracked domain swaps that array.
     feed(ev.toolResult(11, 1, 'c1', 'ECHO'))
     const resolved = session.getSnapshot()