feat(background-process): notify sessions when tasks end

Send synthetic session notifications when background processes finish, fail, stop, or terminate so the originating agent can react without polling. Hide synthetic text-only prompts from the UI stream so operational notifications stay out of the visible transcript.

packages/ui/src/components/message-block.tsx

@@ -3,7 +3,7 @@ import { ChevronsDownUp, ChevronsUpDown, ExternalLink, FoldVertical, ListStart,
 import MessageItem from "./message-item"
 import type { InstanceMessageStore } from "../stores/message-v2/instance-store"
 import type { ClientPart, MessageInfo } from "../types/message"
-import { partHasRenderableText } from "../types/message"
+import { isHiddenSyntheticTextPart, partHasRenderableText } from "../types/message"
 import { buildRecordDisplayData, clearRecordDisplayCacheForInstance } from "../stores/message-v2/record-display-cache"
 import type { MessageRecord } from "../stores/message-v2/types"
 import { messageStoreBus } from "../stores/message-v2/bus"
@@ -231,6 +231,12 @@ function isContentPartType(type: unknown): boolean {
   return type === "text" || type === "file"
 }
 
+function isVisibleContentPart(part: ClientPart): boolean {
+  if (!part || !isContentPartType((part as any).type)) return false
+  if (isHiddenSyntheticTextPart(part)) return false
+  return partHasRenderableText(part)
+}
+
 function MessageContentItem(props: MessageContentItemProps) {
   const record = createMemo(() => props.store().getMessage(props.messageId))
   const messageInfo = createMemo(() => props.store().getMessageInfo(props.messageId))
@@ -264,13 +270,15 @@ function MessageContentItem(props: MessageContentItemProps) {
     return resolved
   })
 
+  const visibleParts = createMemo(() => parts().filter((part) => isVisibleContentPart(part)))
+
   const showAgentMeta = createMemo(() => {
     const current = record()
     if (!current) return false
     if (current.role !== "assistant") return false
 
     const currentParts = parts()
-    if (!currentParts.some((part) => partHasRenderableText(part))) {
+    if (visibleParts().length === 0) {
       return false
     }
 
@@ -286,10 +294,10 @@ function MessageContentItem(props: MessageContentItemProps) {
       if (!isSupportedPartType(part)) continue
 
       if (!isContentPartType((part as any).type)) continue
-      if (partHasRenderableText(part)) {
-        return false
+        if (isVisibleContentPart(part)) {
+          return false
+        }
       }
-    }
 
     return true
   })
@@ -300,7 +308,7 @@ function MessageContentItem(props: MessageContentItemProps) {
         <MessageItem
           record={resolvedRecord()}
           messageInfo={messageInfo()}
-          parts={parts()}
+          parts={visibleParts()}
           instanceId={props.instanceId}
           sessionId={props.sessionId}
           isQueued={isQueued()}

packages/ui/src/components/message-item.tsx

@@ -2,7 +2,7 @@ import { For, Show, createEffect, createSignal, onCleanup } from "solid-js"
 import { Portal } from "solid-js/web"
 import { Copy, ListStart, Split, Trash, Undo } from "lucide-solid"
 import type { MessageInfo, ClientPart, SDKAssistantMessageV2 } from "../types/message"
-import { partHasRenderableText } from "../types/message"
+import { isHiddenSyntheticTextPart, partHasRenderableText } from "../types/message"
 import type { MessageRecord } from "../stores/message-v2/types"
 import MessagePart from "./message-part"
 import { copyToClipboard } from "../lib/clipboard"
@@ -290,9 +290,9 @@ export default function MessageItem(props: MessageItemProps) {
 
   const getRawContent = () => {
     return props.parts
-      .filter(part => part.type === "text")
-      .map(part => (part as { text?: string }).text || "")
-      .filter(text => text.trim().length > 0)
+      .filter((part) => part.type === "text" && !isHiddenSyntheticTextPart(part))
+      .map((part) => (part as { text?: string }).text || "")
+      .filter((text) => text.trim().length > 0)
       .join("\n\n")
   }
 
@@ -338,7 +338,7 @@ export default function MessageItem(props: MessageItemProps) {
     }
   }
 
-  if (!isUser() && !hasContent() && !isGenerating()) {
+  if (!hasContent() && !isGenerating()) {
     return null
   }
 

packages/ui/src/components/message-part.tsx

@@ -33,19 +33,7 @@ export default function MessagePart(props: MessagePartProps) {
   const shouldHideTextPart = () => {
     const part = props.part
     if (!part || part.type !== "text") return false
-
-    const isSynthetic = Boolean((part as any).synthetic)
-    if (!isSynthetic) return false
-
-    // Keep optimistic user prompts visible; hide other synthetic user helper parts.
-    if (props.messageType === "user") {
-      const primaryId = props.primaryUserTextPartId
-      if (!primaryId) return false
-      return part.id !== primaryId
-    }
-
-    // Hide synthetic assistant text.
-    return true
+    return Boolean((part as any).synthetic)
   }
 
 

packages/ui/src/components/message-section.tsx

@@ -46,6 +46,33 @@ export default function MessageSection(props: MessageSectionProps) {
   const showTimelineToolsPreference = () => preferences().showTimelineTools ?? true
   const store = createMemo<InstanceMessageStore>(() => messageStoreBus.getOrCreate(props.instanceId))
   const messageIds = createMemo(() => store().getSessionMessageIds(props.sessionId))
+  const visibleMessageIds = createMemo(() => {
+    const resolvedStore = store()
+    return messageIds().filter((messageId) => {
+      const record = resolvedStore.getMessage(messageId)
+      if (!record) return false
+
+      if (buildTimelineSegments(props.instanceId, record, t).length > 0) {
+        return true
+      }
+
+      if (record.role !== "assistant") {
+        return false
+      }
+
+      const info = resolvedStore.getMessageInfo(messageId)
+      if (!info || info.role !== "assistant") {
+        return false
+      }
+
+      if (info.error) {
+        return true
+      }
+
+      const timeInfo = info.time as { created: number; end?: number } | undefined
+      return Boolean(timeInfo && (timeInfo.end === undefined || timeInfo.end === 0))
+    })
+  })
 
   const scrollCache = useScrollCache({
     instanceId: props.instanceId,
@@ -611,7 +638,7 @@ export default function MessageSection(props: MessageSectionProps) {
     const api = listApi()
     if (!element || !api) return
     if (props.loading) return
-    if (messageIds().length === 0) return
+    if (visibleMessageIds().length === 0) return
     if (didRestoreScroll()) return
 
     scrollCache.restore(element, {
@@ -1003,7 +1030,7 @@ export default function MessageSection(props: MessageSectionProps) {
         data-scroll-buttons={scrollButtonsCount()}
       >
         <VirtualFollowList
-          items={messageIds}
+          items={visibleMessageIds}
           getKey={(messageId) => messageId}
           getAnchorId={getMessageAnchorId}
           getKeyFromAnchorId={getMessageIdFromAnchorId}
@@ -1049,7 +1076,7 @@ export default function MessageSection(props: MessageSectionProps) {
           registerState={(state) => setListState(state)}
           renderBeforeItems={() => (
             <>
-              <Show when={!props.loading && messageIds().length === 0}>
+              <Show when={!props.loading && visibleMessageIds().length === 0}>
                 <div class="empty-state">
                   <div class="empty-state-content">
                     <div class="flex flex-col items-center gap-3 mb-6">

packages/ui/src/components/message-timeline.tsx

@@ -2,6 +2,7 @@ import { For, Show, createEffect, createMemo, createSignal, onCleanup, on, untra
 import MessagePreview from "./message-preview"
 import { messageStoreBus } from "../stores/message-v2/bus"
 import type { ClientPart } from "../types/message"
+import { isHiddenSyntheticTextPart } from "../types/message"
 import type { MessageRecord } from "../stores/message-v2/types"
 import { buildRecordDisplayData } from "../stores/message-v2/record-display-cache"
 import { getPartCharCount } from "../lib/token-utils"
@@ -105,6 +106,7 @@ function collectReasoningText(part: ClientPart): string {
 
 function collectTextFromPart(part: ClientPart, t: (key: string, params?: Record<string, unknown>) => string): string {
   if (!part) return ""
+  if (isHiddenSyntheticTextPart(part)) return ""
   if (typeof (part as any).text === "string") {
     return (part as any).text as string
   }