diff --git a/packages/client/ui-chat/src/client/chat/TurnProcessNodeView.tsx b/packages/client/ui-chat/src/client/chat/TurnProcessNodeView.tsx
index b404787a1a..71dc44693b 100644
--- a/packages/client/ui-chat/src/client/chat/TurnProcessNodeView.tsx
+++ b/packages/client/ui-chat/src/client/chat/TurnProcessNodeView.tsx
@@ -25,9 +25,9 @@ export const TurnProcessNodeView = memo(function TurnProcessNodeView({
   }, [ticking])
   if (turn?.start === undefined && turn?.status !== 'closed') return null
   const canCollapse = turnProcess.foldable && turnProcess.hasContent && !turnProcessAlwaysOpen(node)
-  const running = turn?.status === 'open'
-  const reason = turn?.end?.data.reason.kind
-  const elapsedMs = turn?.start === undefined ? undefined
+  const running = turn.status === 'open'
+  const reason = turn.end?.data.reason.kind
+  const elapsedMs = turn.start === undefined ? undefined
     : Math.max(1000, (turn.end?.time ?? now) - turn.start.time)
   const duration = elapsedMs === undefined ? undefined
     : running ? formatLiveRunDuration(elapsedMs, t) : formatRunDuration(elapsedMs, t)
diff --git a/packages/client/ui-chat/src/index.ts b/packages/client/ui-chat/src/index.ts
index fabb8cf7df..b919f5786a 100644
--- a/packages/client/ui-chat/src/index.ts
+++ b/packages/client/ui-chat/src/index.ts
@@ -9,7 +9,8 @@ import { TRANSCRIPT_VIEW_FIELD } from './chat-settings.ts'
 import { ChatSettingsFields } from './chat-settings.ts'
 
 export {
-  CHAT_SETTINGS_NAMESPACE, DEFAULT_TRANSCRIPT_VIEW_MODE, LEGACY_TRANSCRIPT_VIEW_MODE, LEGACY_EXPANDED_TRANSCRIPT_VIEW_MODE, TRANSCRIPT_VIEW_FIELD,
+  CHAT_SETTINGS_NAMESPACE, DEFAULT_TRANSCRIPT_VIEW_MODE, LEGACY_TRANSCRIPT_VIEW_MODE,
+  LEGACY_EXPANDED_TRANSCRIPT_VIEW_MODE, TRANSCRIPT_VIEW_FIELD,
   TRANSCRIPT_VIEW_MODES, type ChatSettings, type TranscriptViewMode,
 } from './chat-settings.ts'
 
diff --git a/packages/client/ui-tool/src/client/tool/tool-call-arguments-partial.ts b/packages/client/ui-tool/src/client/tool/tool-call-arguments-partial.ts
index 071e3d4fd2..bc55412b4d 100644
--- a/packages/client/ui-tool/src/client/tool/tool-call-arguments-partial.ts
+++ b/packages/client/ui-tool/src/client/tool/tool-call-arguments-partial.ts
@@ -11,13 +11,15 @@ const subscribeEmpty = (): (() => void) => () => {}
  * @returns a Hook that reads only this call's raw argument prefix.
  */
 export const bindToolCallArgumentsPartial: ToolCallInjected['hooks']['toolCallArgumentsPartial'] = (
-  _standard, { assistant, callId },
+  _standard, context,
 ) => {
+  const { assistant, callId } = context
+  const subscribe = assistant === undefined ? subscribeEmpty : (listener: () => void) => assistant.subscribe(listener)
   const getSnapshot = (): string => {
     const block = assistant?.getSnapshot()?.blocks.find(candidate => candidate.kind === 'tool-call' && candidate.callId === callId)
     return block?.kind === 'tool-call' ? block.argsRaw : ''
   }
   return function useToolCallArgumentsPartial() {
-    return useSyncExternalStore(assistant?.subscribe ?? subscribeEmpty, getSnapshot)
+    return useSyncExternalStore(subscribe, getSnapshot)
   }
 }
diff --git a/packages/client/ui-tool/tests/tool-call-arguments-partial.client.spec.tsx b/packages/client/ui-tool/tests/tool-call-arguments-partial.client.spec.tsx
index f1b82985cb..f3e30f81b0 100644
--- a/packages/client/ui-tool/tests/tool-call-arguments-partial.client.spec.tsx
+++ b/packages/client/ui-tool/tests/tool-call-arguments-partial.client.spec.tsx
@@ -28,9 +28,9 @@ function source(initial: AssistantChatData | undefined) {
   const store = createSnapshotStore<AssistantChatData | undefined>(initial)
   const listeners = new Set<() => void>()
   return {
-    set: store.set,
+    set: (value: AssistantChatData | undefined) => { store.set(value) },
     listeners,
-    getSnapshot: store.getSnapshot,
+    getSnapshot: () => store.getSnapshot(),
     subscribe: (listener: () => void) => {
       listeners.add(listener)
       const dispose = store.subscribe(listener)