Improve message stream auto-scroll during streaming

packages/ui/src/stores/instances.ts

@@ -618,6 +618,13 @@ function mutateToolPartPermission(
       draft.updatedAt = Date.now()
     }),
   )
+
+  // Permission attachment/removal can change the rendered height of the
+  // message list (e.g., permission blocks or diffs), so bump the
+  // session revision to ensure auto-scroll reacts.
+  if (messageRecord.sessionId) {
+    store.setState("sessionRevisions", messageRecord.sessionId, (value: number = 0) => value + 1)
+  }
 }
 
 function attachPermissionToToolPart(instanceId: string, permission: Permission, active: boolean): void {

packages/ui/src/stores/message-v2/instance-store.ts

@@ -439,10 +439,10 @@ export function createInstanceMessageStore(instanceId: string): InstanceMessageS
       bufferPendingPart({ messageId: input.messageId, part: input.part, receivedAt: Date.now() })
       return
     }
-
+ 
     const partId = ensurePartId(input.messageId, input.part, message.partIds.length)
     const cloned = clonePart(input.part)
-
+ 
     setState(
       "messages",
       input.messageId,
@@ -463,8 +463,13 @@ export function createInstanceMessageStore(instanceId: string): InstanceMessageS
         }
       }),
     )
+ 
+    // Any part update can change the rendered height of the message
+    // list, so we treat it as a session revision for scroll purposes.
+    bumpSessionRevision(message.sessionId)
   }
 
+
   function flushPendingParts(messageId: string) {
     const pending = state.pendingParts[messageId]
     if (!pending || pending.length === 0) {

packages/ui/src/stores/session-events.ts

@@ -81,20 +81,25 @@ function handleMessageUpdate(instanceId: string, event: MessageUpdateEvent | Mes
   if (event.type === "message.part.updated") {
     const rawPart = event.properties?.part
     if (!rawPart) return
-
+ 
     const part = normalizeMessagePart(rawPart)
-    const sessionId = typeof part.sessionID === "string" ? part.sessionID : undefined
-    const messageId = typeof part.messageID === "string" ? part.messageID : undefined
+    const messageInfo = (event as any)?.properties?.message as MessageInfo | undefined
+ 
+    const fallbackSessionId = typeof messageInfo?.sessionID === "string" ? messageInfo.sessionID : undefined
+    const fallbackMessageId = typeof messageInfo?.id === "string" ? messageInfo.id : undefined
+ 
+    const sessionId = typeof part.sessionID === "string" ? part.sessionID : fallbackSessionId
+    const messageId = typeof part.messageID === "string" ? part.messageID : fallbackMessageId
     if (!sessionId || !messageId) return
-
+ 
     const session = instanceSessions.get(sessionId)
     if (!session) return
-
+ 
     const store = messageStoreBus.getOrCreate(instanceId)
-    const messageInfo = (event as any)?.properties?.message as MessageInfo | undefined
     const role: MessageRole = resolveMessageRole(messageInfo)
     const createdAt = typeof messageInfo?.time?.created === "number" ? messageInfo.time.created : Date.now()
 
+
     let record = store.getMessage(messageId)
     if (!record) {
       const pendingId = findPendingMessageId(store, sessionId, role)
@@ -119,8 +124,9 @@ function handleMessageUpdate(instanceId: string, event: MessageUpdateEvent | Mes
     if (messageInfo) {
       upsertMessageInfoV2(instanceId, messageInfo, { status: "streaming" })
     }
+ 
+    applyPartUpdateV2(instanceId, { ...part, sessionID: sessionId, messageID: messageId })
 
-    applyPartUpdateV2(instanceId, part)
 
     updateSessionInfo(instanceId, sessionId)
     refreshPermissionsForSession(instanceId, sessionId)