round 1: project the web transcript from append-origin events

Replace the surface-ordered fold with a log-ordered human transcript:
append-origin surface events at their own log positions plus one marker per
landed compaction checkpoint. Command folding, the tool-call index, and the
rev-keyed memo carry over unchanged.

Removes foldDegraded, the padding sentinels, baseSeq, and degradedSeqs() --
they existed only to satisfy the core fold's seq === index assertion. That
also closes the pagination hole A1 exposed: a page can carry a checkpoint
whose shadowed range fell outside the window, and nothing resolves
surfaceOp.start anymore.

packages/client/ui-conversation/src/client/chat/CompactionItem.tsx

@@ -0,0 +1,49 @@
+// CompactionItem: the one row a landed compaction contributes to the flow.
+// The conversation it shadowed on the model surface stays above it, so this
+// marker reports where the model stopped seeing that history — it never
+// replaces it. The framed checkpoint payload is written for the model and is
+// not rendered; the disclosure shows the summary from the checkpoint's own
+// provenance, and a window cut that left that provenance outside makes the row
+// non-expandable rather than empty.
+
+import { memo, useState } from 'react'
+import type { CompactionSummaryNode } from '@deepseek-ai/dsh-client-runtime/client'
+import {
+  IconChevronDownOutline14,
+  IconChevronRightOutline14,
+  MarkdownText,
+} from '@deepseek-ai/dsh-client-ui-primitives'
+import css from './MessageItem.module.css'
+
+/**
+ * The collapsed-by-default compaction marker.
+ * @param props - the marker node off the snapshot cache.
+ * @returns the marker row, with the summary disclosure when one is available.
+ */
+export const CompactionItem = memo(function CompactionItem({ node }: { node: CompactionSummaryNode }) {
+  const [expanded, setExpanded] = useState(false)
+  const expandable = node.summary !== null
+  const open = expandable && expanded
+  return (
+    <div className={css.compactionRow}>
+      <button
+        type="button"
+        className={css.compactionButton}
+        disabled={!expandable}
+        aria-expanded={expandable ? open : undefined}
+        onClick={() => { setExpanded(value => !value) }}
+      >
+        <span className={css.compactionLeading}>
+          {open ? <IconChevronDownOutline14 /> : <IconChevronRightOutline14 />}
+        </span>
+        <span className={css.compactionTitle}>上下文已压缩</span>
+        <span className={css.compactionSep} aria-hidden />
+        <span className={css.compactionSummary}>
+          {expandable ? '点击查看压缩摘要' : '压缩摘要不可用'}
+        </span>
+      </button>
+      {open && node.summary !== null
+        && <div className={css.compactionBody}><MarkdownText text={node.summary} /></div>}
+    </div>
+  )
+})

packages/client/ui-conversation/src/client/chat/MessageItem.module.css

@@ -42,6 +42,81 @@
   padding: 2px 0;
 }
 
+/* Compaction marker: one dim 24px row with a chevron disclosure for the
+   summary body. Dimmed title (not label-primary) — the row is a boundary
+   notice, not conversation content. */
+.compactionRow {
+  padding: 2px 0;
+}
+
+.compactionButton {
+  display: flex;
+  align-items: center;
+  width: 100%;
+  height: 24px;
+  min-width: 0;
+  padding: 0;
+  border: none;
+  border-radius: 6px;
+  background: none;
+  color: inherit;
+  font: inherit;
+  text-align: left;
+}
+
+.compactionButton:not(:disabled) {
+  cursor: pointer;
+}
+
+.compactionButton:not(:disabled):hover {
+  background: var(--dsw-alias-interactive-bg-hover);
+}
+
+.compactionLeading {
+  flex: none;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: 16px;
+  height: 16px;
+  margin-right: 6px;
+  color: var(--dsw-alias-label-secondary);
+}
+
+.compactionTitle {
+  flex: none;
+  font-size: 14px;
+  line-height: 24px;
+  color: var(--dsw-alias-label-primary-dimmed);
+}
+
+.compactionSep {
+  flex: none;
+  width: 2px;
+  height: 2px;
+  margin: 0 8px;
+  border-radius: 1px;
+  background: var(--dsw-alias-label-caption);
+}
+
+.compactionSummary {
+  flex: 1 1 auto;
+  min-width: 0;
+  overflow: hidden;
+  color: var(--dsw-alias-label-tertiary);
+  font-size: 14px;
+  line-height: 24px;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.compactionBody {
+  padding: 4px 0 4px 22px;
+  color: var(--dsw-alias-label-tertiary);
+  font-size: 14px;
+  line-height: 24px;
+}
+
 /* Reference chip projection inside a user bubble (`<skill>name</skill>` model
    spans render as chips; free geometry — no textarea pairing here). */
 .refChip {

packages/client/ui-conversation/src/client/chat/MessageItem.tsx

@@ -1,20 +1,21 @@
-// MessageItem: the four simple node kinds — user bubble (right-aligned, with
+// MessageItem: the five simple node kinds — user bubble (right-aligned, with
 // clock + copy / branch / edit IconActions), steering (badged bubble), context
-// injection and unknown-surface JSON rows. Props are frozen node slices off
-// the snapshot cache; memo holds across streaming because unchanged nodes
-// keep their references.
+// injection, the compaction marker, and unknown-surface JSON rows. Props are
+// frozen node slices off the snapshot cache; memo holds across streaming
+// because unchanged nodes keep their references.
 
 import { memo } from 'react'
 import type { ReactNode } from 'react'
 import type {
-  ContextMessageNode, SteeringMessageNode, UnknownSurfaceNode, UserMessageNode,
+  CompactionSummaryNode, ContextMessageNode, SteeringMessageNode, UnknownSurfaceNode, UserMessageNode,
 } from '@deepseek-ai/dsh-client-runtime/client'
 import { JsonBlock, MessageText } from '@deepseek-ai/dsh-client-ui-primitives'
+import { CompactionItem } from './CompactionItem.tsx'
 import { MessageIconActions } from './MessageIconActions.tsx'
 import css from './MessageItem.module.css'
 
 export interface MessageItemProps {
-  node: UserMessageNode | SteeringMessageNode | ContextMessageNode | UnknownSurfaceNode
+  node: UserMessageNode | SteeringMessageNode | ContextMessageNode | CompactionSummaryNode | UnknownSurfaceNode
 }
 
 function contentText(content: readonly unknown[]): { text: string; rest: unknown[] } {
@@ -98,6 +99,8 @@ export const MessageItem = memo(function MessageItem({ node }: MessageItemProps)
           <JsonBlock label="上下文注入" payload={{ content: node.content, source: node.source }} />
         </div>
       )
+    case 'compaction':
+      return <CompactionItem node={node} />
     default:
       return (
         <div className={css.contextRow}>

packages/client/ui-conversation/src/client/chat/chat-flow.ts

@@ -24,7 +24,7 @@ function rendersNothing(node: ConversationNode): boolean {
 
 /**
  * Group finalized nodes into the step-summary flow.
- * @param nodes - snapshot nodes (surface order).
+ * @param nodes - snapshot nodes (human transcript order).
  * @returns flow items; consecutive tool-results merged into one group keyed by the first seq.
  */
 export function deriveChatFlow(nodes: readonly ConversationNode[]): ChatFlowItem[] {