fix(app): hydrate timeline message parents (#35269)

packages/app/src/pages/session/timeline/model.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, test } from "bun:test"
 import type { AssistantMessage, Message, UserMessage } from "@opencode-ai/sdk/v2"
-import { loadOlderTimeline, selectUserMessages, selectVisibleUserMessages } from "./model"
+import { isTimelineReady, loadOlderTimeline, selectUserMessages, selectVisibleUserMessages } from "./model"
 
 const user = (id: string) => ({ id, role: "user" }) as UserMessage
 const assistant = (id: string) => ({ id, role: "assistant" }) as AssistantMessage
@@ -15,6 +15,12 @@ describe("timeline model", () => {
     expect(selectVisibleUserMessages(users)).toBe(users)
   })
 
+  test("waits for an assistant-only load to hydrate its user root", () => {
+    expect(isTimelineReady([assistant("msg_2")], true)).toBe(false)
+    expect(isTimelineReady([user("msg_1"), assistant("msg_2")], true)).toBe(true)
+    expect(isTimelineReady([], false)).toBe(true)
+  })
+
   test("loads exactly one opaque cursor page", async () => {
     let calls = 0
     const anchors: Array<string | boolean> = []

packages/app/src/pages/session/timeline/model.ts

@@ -45,7 +45,7 @@ export function createTimelineModel(input: {
   })
   const ready = createMemo(() => {
     const id = input.sessionID()
-    return !id || sync().data.message[id] !== undefined
+    return !id || isTimelineReady(sync().data.message[id], serverSync().session.history.loading(id))
   })
   const userMessages = createMemo(() => selectUserMessages(messages()), emptyUserMessages, { equals: same })
   const visibleUserMessages = createMemo(
@@ -98,6 +98,10 @@ export function selectUserMessages(messages: Message[]) {
   return messages.filter((message): message is UserMessage => message.role === "user")
 }
 
+export function isTimelineReady(messages: Message[] | undefined, loading: boolean) {
+  return messages !== undefined && (messages.some((message) => message.role === "user") || !loading)
+}
+
 export function selectVisibleUserMessages(messages: UserMessage[], revertMessageID?: string) {
   if (!revertMessageID) return messages
   return messages.filter((message) => message.id < revertMessageID)