fix(ui): stabilize workplace chat scrolling

opc/plugins/office_ui/frontend_src/lib/messageTimelineIdentity.ts

@@ -0,0 +1,30 @@
+import type { ChatMessage } from '../types/chat'
+
+export function stableMessageTimelineKey(message: ChatMessage): string {
+  const metadata = message.metadata ?? {}
+  const checkpointId = String(metadata.checkpoint_id ?? '').trim()
+  if (checkpointId) return `checkpoint:${checkpointId}`
+
+  const uiMessageId = String(metadata.ui_message_id ?? '').trim()
+  const transcriptKind = String(metadata.transcript_kind ?? metadata.kind ?? '').trim()
+  const metadataRole = String((metadata as Record<string, unknown>).role ?? '').trim().toLowerCase()
+  const isUserTurn = message.sender === 'user'
+    || metadataRole === 'user'
+    || transcriptKind === 'runtime_v2_user_turn'
+    || transcriptKind === 'top_level_user_turn'
+  // The optimistic and persisted user surfaces share one client identity.
+  if (isUserTurn && uiMessageId) return `ui:${uiMessageId}`
+
+  // ChatStore attaches this only when one semantic result surface replaces
+  // another. It preserves the already-mounted row without entering protocol
+  // or persistence data.
+  const retainedTimelineId = String(metadata.ui_timeline_id ?? '').trim()
+  if (retainedTimelineId) return retainedTimelineId
+
+  const turnId = String(metadata.canonical_turn_id ?? metadata.turn_id ?? '').trim()
+  if (!isUserTurn && turnId && transcriptKind === 'runtime_v2_assistant') {
+    return `turn:assistant:${turnId}`
+  }
+
+  return `message:${message.id}`
+}