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.