fix(tui,host): project the human transcript from append-origin events

The terminal and history pagination both treated the model-visible surface as
the human transcript. A landed compaction replacement therefore erased the
conversation it summarized — messages the reader had already seen — and a
model-only replacement copy consumed a page's `maxMessages` quota, which could
also split a compaction's provenance from the replacement citing it.

`dsh-session` now exports the marker split `isAppendSurfaceEvent` /
`isReplacementSurfaceEvent`. The terminal replays append-origin surface events,
keeps a shadowed step's tool cards paired through its append-origin assistant
message, and renders one dim marker where a compaction landed; the checkpoint is
recognized through the compaction seam's `isCompactCheckpointSource` contract,
not the shape of the replacement. `session.history` counts only append-origin
human messages. Everything model-facing keeps reading `session.surface`.

packages/ui/tui/src/chat/helpers.ts

@@ -1,6 +1,6 @@
 /**
  * Zero-state helpers for the interactive chat channel: prompt-directory and
- * Git-branch formatting, surface/tool-call derivations over the session log,
+ * Git-branch formatting, transcript/tool-call derivations over the session log,
  * session-reference context cards, the placeholder editor, and banner-reveal
  * timing constants. None of these close over channel state.
  * @module @deepseek-ai/dsh-tui/chat/helpers
@@ -15,7 +15,9 @@ import {
   truncateToWidth,
   visibleWidth,
 } from '@earendil-works/pi-tui'
-import type { Session } from '@deepseek-ai/dsh-session'
+import { isCompactCheckpointSource } from '@deepseek-ai/dsh-compact'
+import { isAppendSurfaceEvent, isReplacementSurfaceEvent } from '@deepseek-ai/dsh-session'
+import type { Session, SessionEvent } from '@deepseek-ai/dsh-session'
 
 /** Editor that shows a placeholder without making it editable content. */
 export class HintEditor extends Editor {
@@ -83,24 +85,16 @@ export function gitBranch(cwd: string): string | undefined {
 }
 
 /**
- * Sequence numbers currently visible on the session surface.
- * @param session - session whose surface nodes to read.
- * @returns the set of visible event sequence numbers.
- */
-export function activeSurfaceSeqs(session: Session): Set<number> {
-  return new Set(session.surface.nodes)
-}
-
-/**
- * Tool-call ids whose owning assistant message is on the active surface.
+ * Tool-call ids whose owning assistant message is append-origin, so its tool
+ * cards stay paired in the transcript after a replacement shadowed the message
+ * on the model surface.
  * @param session - session whose events to scan.
- * @param active - sequence numbers currently on the surface.
- * @returns the set of active tool-call ids.
+ * @returns the set of transcript tool-call ids.
  */
-export function activeToolCallIds(session: Session, active: ReadonlySet<number>): Set<string> {
+export function transcriptToolCallIds(session: Session): Set<string> {
   const ids = new Set<string>()
   for (const event of session.events) {
-    if (event.type !== 'assistant/message' || !active.has(event.seq)) continue
+    if (event.type !== 'assistant/message' || !isAppendSurfaceEvent(event)) continue
     for (const block of event.data.message.content) {
       if (block.type === 'tool-call') ids.add(block.id)
     }
@@ -108,6 +102,22 @@ export function activeToolCallIds(session: Session, active: ReadonlySet<number>)
   return ids
 }
 
+/**
+ * Whether an event is a landed compaction checkpoint. Recognition goes through
+ * {@link isCompactCheckpointSource} — the compaction seam's backend-independent
+ * contract for the source every backend stamps on its replacement user message —
+ * rather than the shape of the replacement. Other replacements (a pruned
+ * `tool/result`, a regenerated `assistant/message`) rewrite one node for the
+ * model and mark no boundary in the conversation.
+ * @param event - event to test.
+ * @returns true when the event compacted a surface range.
+ */
+export function isCompactCheckpoint(event: SessionEvent): boolean {
+  return event.type === 'user/message'
+    && isCompactCheckpointSource(event.data.source)
+    && isReplacementSurfaceEvent(event)
+}
+
 /**
  * Read a session-reference context card's display labels from an event source.
  * @param source - event source to inspect.

packages/ui/tui/src/index.ts

@@ -35,6 +35,9 @@ import type { ContentBlock, MessageId } from '@deepseek-ai/dsh-llm'
 import type {} from '@deepseek-ai/dsh-llm-retry'
 import { renderPrompt } from '@deepseek-ai/dsh-system-prompt'
 import {
+  isAppendSurfaceEvent,
+  isReplacementSurfaceEvent,
+  isSurfaceEligibleType,
   SessionId,
   type SessionEvent,
   type UserMessage,
@@ -118,14 +121,14 @@ import {
 } from './chat/skill-invocation.ts'
 import { ReferenceAutocompleteProvider } from './chat/autocomplete.ts'
 import {
-  activeSurfaceSeqs,
-  activeToolCallIds,
   BANNER_REVEAL_INTERVAL_MS,
   BANNER_REVEAL_STEPS,
   formatCwd,
   gitBranch,
   HintEditor,
+  isCompactCheckpoint,
   sessionReferenceCard,
+  transcriptToolCallIds,
 } from './chat/helpers.ts'
 import {
   createModelController,
@@ -268,6 +271,13 @@ export const inject = ['agents', 'sessions', 'commands', 'userInteraction', 'too
 /** Model guidance for path-only file references selected through the TUI. */
 export const FILE_REFERENCE_PROMPT = 'Paths prefixed with @ are files explicitly referenced by the user. Use the read tool when their contents are needed; do not claim to have inspected a file before reading it.'
 
+/**
+ * Transcript row standing in for one compacted range. The conversation the
+ * compaction replaced stays rendered above it: the marker reports where the
+ * model stopped seeing that history, not that the history is gone.
+ */
+const COMPACTION_MARKER = '… earlier context was compacted …'
+
 interface RunningStatus {
   turn: number | undefined
   timer: ReturnType<typeof setInterval>
@@ -816,6 +826,17 @@ export function createTuiChat(
     }
   }
 
+  const renderCompactionMarker = (): void => {
+    chat.addChild(new Spacer(1))
+    chat.addChild(new Text(palette.dim(COMPACTION_MARKER), 0, 0))
+  }
+
+  /**
+   * Replay the human transcript from the append-only log. The model-visible
+   * surface shadows compacted ranges, so it is not the source here: every
+   * append-origin message stays rendered, and a replacement contributes at most
+   * the compaction marker at its own log position.
+   */
   const rebuildTranscript = (populateHistory: boolean): void => {
     chat.clear()
     toolCards.clear()
@@ -823,15 +844,13 @@ export function createTuiChat(
     contextCards.clear()
     streaming = undefined
     todo.update([])
-    const active = activeSurfaceSeqs(agent.session)
-    const activeCalls = activeToolCallIds(agent.session, active)
+    const transcriptCalls = transcriptToolCallIds(agent.session)
     for (const event of agent.session.events) {
-      const isSurface = event.type === 'user/message'
-        || event.type === 'assistant/message'
-        || event.type === 'tool/result'
-        || event.type === 'steering/message'
-      if (isSurface && !active.has(event.seq)) continue
-      if (event.type === 'tool/call' && !activeCalls.has(event.data.callId)) continue
+      if (isSurfaceEligibleType(event.type) && !isAppendSurfaceEvent(event)) {
+        if (isCompactCheckpoint(event)) renderCompactionMarker()
+        continue
+      }
+      if (event.type === 'tool/call' && !transcriptCalls.has(event.data.callId)) continue
       renderEvent(event, { addHistory: populateHistory, renderChunks: false })
     }
     requestRender()
@@ -1438,8 +1457,11 @@ export function createTuiChat(
     recordEventUsage(tokens, event)
     if (event.type === 'turn/start' && runningStatus !== undefined) runningStatus.turn = event.data.turn
     if (event.type === 'assistant/message' && streaming?.isSettled()) streaming = undefined
-    if ('surfaceOp' in event && typeof event.surfaceOp === 'object') {
-      rebuildTranscript(false)
+    // A replacement mutates only the model surface, so the rendered transcript
+    // keeps what it already showed; a landed summary checkpoint adds its marker.
+    if (isReplacementSurfaceEvent(event)) {
+      if (isCompactCheckpoint(event)) renderCompactionMarker()
+      requestRender()
       return
     }
     renderEvent(event, { addHistory: false, renderChunks: true })