fix(ui): keep live tool presentation after turn completion

Turn completion no longer force-scrolls the conversation: only a
session switch snaps to the bottom, so finishing a turn does not yank
the view while the user reads. ACP streams richer tool titles (for
example a workflow run's description) than the persisted tool/call
name; remember them per call id and keep rendering them in chat and
trajectory after the persisted trace replaces the live turn.

packages/ui/desktop/src/app.ts

@@ -157,6 +157,7 @@ const state = {
   expandedActivityIds: new Set<string>(),
   traceLoadRevision: 0,
   liveTurnCounter: 0,
+  liveToolTitles: new Map<string, string>(),
   traceCatchupTimer: undefined as number | undefined,
   traceCatchupAttempts: 0,
 }
@@ -488,7 +489,7 @@ function applyTrace(trace: TracePayload, resetExpansion: boolean): void {
   renderTrajTree()
   renderWaterfall()
   renderInspector()
-  scrollChatToBottom(true)
+  scrollChatToBottom(resetExpansion)
   scheduleTraceCatchup(sessionId)
 }
 
@@ -563,6 +564,7 @@ function handleSessionUpdate(payload: SessionUpdatePayload): void {
     live.status = 'streaming'
   } else if (kind === 'tool_call' || kind === 'tool_call_update') {
     const callId = String(update.toolCallId ?? `tool-${live.tools.length}`)
+    if (typeof update.title === 'string' && update.title.length > 0) state.liveToolTitles.set(callId, update.title)
     const existing = live.tools.find(tool => tool.callId === callId)
     const title = String(update.title ?? existing?.title ?? t('chat.toolUse'))
     const status = String(update.status ?? existing?.status ?? '')
@@ -953,9 +955,15 @@ function renderConversationActivity(activity: ChatActivity): string {
   `
 }
 
+/** ACP streams richer tool titles than the persisted name; keep them after the turn. */
+function liveToolTitle(target: TraceTarget): string | undefined {
+  return state.liveToolTitles.get(target.id.replace(/^tool:/, ''))
+}
+
 function renderChatToolActivity(target: TraceTarget): string {
   const failed = target.status === 'error'
-  const preview = toolCallPreview(target.input)
+  const richTitle = liveToolTitle(target)
+  const preview = richTitle === undefined ? toolCallPreview(target.input) : ''
   const expanded = state.expandedActivityIds.has(target.id)
   const inputHtml = `<div class="activity-section-title">${escapeHtml(t('chat.input'))}</div><pre>${escapeHtml(formatPayload(target.input, 'json'))}</pre>`
   const outputHtml = target.output === '' ? '' : `<div class="activity-section-title">${escapeHtml(failed ? t('chat.errorOutput') : t('chat.output'))}</div><pre>${escapeHtml(formatPayload(target.output, 'plain'))}</pre>`
@@ -964,7 +972,7 @@ function renderChatToolActivity(target: TraceTarget): string {
   return `
     <section class="chat-activity tool-use ${failed ? 'failed' : ''} ${selectedTargetClass(target.id)}">
       <div class="activity-row">
-        <button class="activity-select" type="button" data-target-id="${escapeHtml(target.id)}"><span>${escapeHtml(failed ? t('chat.toolFailed') : t('chat.toolUse'))}</span><strong>${escapeHtml(target.title)}${preview.length > 0 ? `<span class="activity-preview"> · ${escapeHtml(preview)}</span>` : ''}</strong></button>
+        <button class="activity-select" type="button" data-target-id="${escapeHtml(target.id)}"><span>${escapeHtml(failed ? t('chat.toolFailed') : t('chat.toolUse'))}</span><strong>${escapeHtml(richTitle ?? target.title)}${preview.length > 0 ? `<span class="activity-preview"> · ${escapeHtml(preview)}</span>` : ''}</strong></button>
         <button class="activity-toggle" type="button" data-toggle-activity="${escapeHtml(target.id)}" aria-expanded="${expanded}" aria-controls="act-${escapeHtml(target.id)}" aria-label="${escapeHtml(t(expanded ? 'trace.collapseRow' : 'trace.expandRow'))}">${expanded ? '⌃' : '⌄'}</button>
       </div>
       <div class="activity-body" id="act-${escapeHtml(target.id)}" ${expanded ? '' : 'hidden'} data-target-id="${escapeHtml(target.id)}">${inputHtml}${outputHtml}${spawnedHtml}</div>
@@ -1091,6 +1099,8 @@ function trajectoryRowTitle(target: TraceTarget): string {
     if (preview.length > 0) return preview
   }
   if (target.kind === 'tool') {
+    const rich = liveToolTitle(target)
+    if (rich !== undefined) return rich
     const preview = toolCallPreview(target.input)
     return preview.length > 0 ? `${target.title} · ${preview}` : `${target.title} · ${target.subtitle}`
   }

packages/ui/desktop/tests/renderer.spec.ts

@@ -238,6 +238,7 @@ describe('desktop renderer chat lifecycle', () => {
   it('starts a fresh live skeleton per turn and converges without user action when the persisted trace lags', async () => {
     const prompts: Deferred<unknown>[] = [deferred(), deferred(), deferred()]
     const promptQueue = [...prompts]
+    let update: ((payload: unknown) => void) | undefined
     let traceRead: unknown
     const turnEvents = (turn: number, userText: string, answer: string, base: number): unknown[] => [
       { type: 'turn/start', seq: base, time: base + 1, data: { turn, trigger: { kind: 'message' } } },
@@ -253,6 +254,8 @@ describe('desktop renderer chat lifecycle', () => {
       ...turnEvents(1, 'first', 'first answer', 0),
       ...turnEvents(2, 'second', 'second answer', 10),
       ...turnEvents(3, 'third', 'third answer', 20),
+      { type: 'tool/call', seq: 30, time: 31, data: { turn: 3, step: 1, callId: 'wf-1', name: 'workflow', arguments: '{"name":"audit"}' } },
+      { type: 'tool/result', seq: 31, time: 32, data: { turn: 3, step: 1, callId: 'wf-1', content: [{ type: 'text', text: 'done' }] } },
     ])
     traceRead = turn1Trace
 
@@ -272,7 +275,10 @@ describe('desktop renderer chat lifecycle', () => {
         prompt: async () => promptQueue.shift()!.promise,
         cancel: async () => ({}),
         reveal: async () => ({}),
-        onUpdate: () => () => {},
+        onUpdate: (callback: (payload: unknown) => void) => {
+          update = callback
+          return () => {}
+        },
       },
       trace: { read: async () => traceRead },
       feedback: { list: async () => [], add: async () => ({}) },
@@ -312,6 +318,8 @@ describe('desktop renderer chat lifecycle', () => {
     await vi.waitFor(() => {
       expect(document.querySelector('#liveTurn .user-bubble')?.textContent).toBe('third')
     })
+    // The ACP stream carries a richer tool title than the persisted name.
+    update?.({ sessionId: 's-lag', update: { sessionUpdate: 'tool_call', toolCallId: 'wf-1', title: 'workflow: run audit agents', status: 'in_progress' } })
 
     // Once the persisted log catches up, the view converges with no user action.
     prompts[2]!.resolve({ response: {}, trace: turn1Trace })
@@ -320,5 +328,7 @@ describe('desktop renderer chat lifecycle', () => {
       expect(document.querySelector('#conversation')?.textContent).toContain('third answer')
       expect(document.querySelector('#liveTurn')?.innerHTML).toBe('')
     }, { timeout: 4000 })
+    // The live workflow presentation survives the switch to the persisted view.
+    expect(document.querySelector('#conversation')?.textContent).toContain('workflow: run audit agents')
   })
 })