Keep conversation turns distinct and history stable (#7990)

* fix(app): keep autonomous turns distinct and readable

Hidden system prompts merged autonomous work into the previous response and reopened completed turns. Preserve canonical turn boundaries and expose their triggers, while making received messages attributable and expanded turn details readable in one step.

* fix(timeline): mount history at actual run boundaries

* fix(timeline): load and retain complete available turns

* fix(app): summarize actions and preserve conversation events

* test(timeline): verify whole-turn paging stays responsive

* fix(app): group reasoning according to thinking preference

* test(app): align history journeys with whole-turn loading

packages/app/src/agent-stream/presentation.ts

@@ -1,3 +1,4 @@
+import { isTurnBoundary } from "./turn-membership";
 import type { ChatDisplay } from "@/hooks/use-settings";
 import type { TimelineItemTransform } from "@/plugins/timeline/model";
 import { projectPluginTimelineItems } from "@/plugins/timeline/projection";
@@ -16,9 +17,11 @@ interface PresentationInput {
   head: StreamItem[];
   transform: TimelineItemTransform | undefined;
   display: ChatDisplay;
+  autoExpandReasoning?: boolean;
   /** User messages whose collapsed turn the reader opened. */
   expandedTurnHostIds: ReadonlySet<string>;
   isTurnActive: boolean;
+  activeTurnId?: string | null;
 }
 
 export interface StreamPresentation extends ToolCallDetailProjection {
@@ -55,6 +58,7 @@ export function createStreamPresentation() {
   let historyTransform: TimelineItemTransform | undefined;
   let historyRows: StreamItem[] = [];
   let preparedTail: StreamItem[] | undefined;
+  let preparedAutoExpandReasoning: boolean | undefined;
   let preparedLevel: ToolCallDetailLevel | undefined;
   let preparedHistory: PreparedToolCallHistory | null = null;
   let collapsedSource: StreamItem[] | undefined;
@@ -63,6 +67,22 @@ export function createStreamPresentation() {
   let collapsed: TurnCollapse | undefined;
 
   function presentRows(item: StreamItem): StreamItem[] {
+    if (item.kind === "tool_call" && item.payload.source === "agent") {
+      const message = item.payload.data.agentMessage;
+      if (message?.event === "message") {
+        return [
+          {
+            kind: "user_message",
+            id: item.id,
+            turnId: item.turnId,
+            timelineCursor: item.timelineCursor,
+            timestamp: item.timestamp,
+            text: message.text,
+            sender: message.sender,
+          },
+        ];
+      }
+    }
     return [item.kind === "user_message" ? presentUserMessage(item) : item];
   }
 
@@ -75,7 +95,14 @@ export function createStreamPresentation() {
     }
     // Live text updates reach the head only, so the folded history is reused until the
     // retained rows, the latest turn's liveness, or the reader's expanded turns change.
-    const isLatestTurnOpen = input.isTurnActive || projection.head.length > 0;
+    const isLatestTurnOpen =
+      (input.isTurnActive || projection.head.length > 0) &&
+      !isTurnBoundary(projection.tail.at(-1) ?? null, projection.head[0] ?? null) &&
+      !(
+        input.activeTurnId &&
+        projection.tail.at(-1)?.turnId &&
+        input.activeTurnId !== projection.tail.at(-1)?.turnId
+      );
     if (
       !collapsed ||
       collapsedSource !== projection.tail ||
@@ -84,6 +111,7 @@ export function createStreamPresentation() {
     ) {
       collapsed = collapseTurns({
         tail: projection.tail,
+        autoExpandReasoning: input.autoExpandReasoning,
         isLatestTurnOpen,
         expandedHostIds: input.expandedTurnHostIds,
         getGroupedCalls: (itemId) => projection.groupsByHostId.get(itemId)?.run.calls,
@@ -93,7 +121,20 @@ export function createStreamPresentation() {
       collapsedExpandedHostIds = input.expandedTurnHostIds;
     }
     const { tail, ...turns } = collapsed;
-    return { ...projection, tail, turns };
+    if (turns.nestedItemIds.size === 0) return { ...projection, tail, turns };
+    // Opening a turn reveals its raw calls; those rows must not become group hosts again.
+    const withoutExpandedRows = (groups: StreamPresentation["groupsByHostId"]) => ({
+      size: groups.size - [...turns.nestedItemIds].filter((id) => groups.has(id)).length,
+      get: (id: string) => (turns.nestedItemIds.has(id) ? undefined : groups.get(id)),
+      has: (id: string) => !turns.nestedItemIds.has(id) && groups.has(id),
+    });
+    return {
+      ...projection,
+      tail,
+      turns,
+      groupsByHostId: withoutExpandedRows(projection.groupsByHostId),
+      historyGroupUpdatesByHostId: withoutExpandedRows(projection.historyGroupUpdatesByHostId),
+    };
   }
 
   return (input: PresentationInput): StreamPresentation => {
@@ -111,10 +152,15 @@ export function createStreamPresentation() {
       const blocks = presentRows(item);
       head.push(...blocks);
     }
-    if (preparedTail !== historyRows || preparedLevel !== level) {
-      preparedHistory = prepareToolCallHistory(level, historyRows);
+    if (
+      preparedTail !== historyRows ||
+      preparedLevel !== level ||
+      preparedAutoExpandReasoning !== input.autoExpandReasoning
+    ) {
+      preparedHistory = prepareToolCallHistory(level, historyRows, input.autoExpandReasoning);
       preparedTail = historyRows;
       preparedLevel = level;
+      preparedAutoExpandReasoning = input.autoExpandReasoning;
     }
     return collapse(
       projectToolCallDetailLevel({