diff --git a/src/renderer/src/components/activity/activity-search-query-work-budget.test.tsx b/src/renderer/src/components/activity/activity-search-query-work-budget.test.tsx
new file mode 100644
index 00000000000..e10b55728cb
--- /dev/null
+++ b/src/renderer/src/components/activity/activity-search-query-work-budget.test.tsx
@@ -0,0 +1,254 @@
+// @vitest-environment happy-dom
+import { act, cleanup, renderHook } from '@testing-library/react'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import type { AgentStatusEntry } from '../../../../shared/agent-status-types'
+import { makePaneKey } from '../../../../shared/stable-pane-id'
+import { toSshExecutionHostId } from '../../../../shared/execution-host'
+import * as clipboard from '../../../../shared/clipboard-text'
+import { useAppStore } from '@/store'
+import {
+  LEAF_ID,
+  makeRepo,
+  makeTabWithIds,
+  makeWorktree
+} from './ActivityPrototypePage-test-fixtures'
+import {
+  activityThreadMatchesSearchQuery,
+  createActivityThreadSearchMatcher,
+  getThreadSearchTextComputeCount
+} from './activity-thread-grouping'
+import { useAgentPaneThreads } from './use-agent-pane-threads'
+
+vi.mock('@/store', async () => {
+  const { createTestStore } = await import('@/store/slices/store-test-helpers')
+  return { useAppStore: createTestStore() }
+})
+
+afterEach(() => {
+  cleanup()
+  vi.restoreAllMocks()
+})
+
+function installThreads(count: number, prompt = 'Task PROJECT ☃ progress'): string[] {
+  vi.spyOn(Date, 'now').mockReturnValue(100_000)
+  const repo = makeRepo()
+  const worktree = makeWorktree()
+  const tabs = Array.from({ length: count }, (_, index) =>
+    makeTabWithIds(`tab-${index}`, worktree.id)
+  )
+  const entries: Record<string, AgentStatusEntry> = {}
+  for (const tab of tabs) {
+    const paneKey = makePaneKey(tab.id, LEAF_ID)
+    entries[paneKey] = {
+      paneKey,
+      state: 'working',
+      prompt,
+      agentType: 'claude',
+      updatedAt: 100_000,
+      stateStartedAt: 99_000,
+      stateHistory: []
+    }
+  }
+  useAppStore.setState({
+    agentStatusByPaneKey: entries,
+    retainedAgentsByPaneKey: {},
+    migrationUnsupportedByPtyId: {},
+    runtimeAgentOrchestrationByPaneKey: {},
+    acknowledgedAgentsByPaneKey: {},
+    activityClearedAtByPaneKey: {},
+    repos: [repo],
+    worktreesByRepo: { [repo.id]: [worktree] },
+    folderWorkspaces: [],
+    detectedWorktreesByRepo: {},
+    tabsByWorktree: { [worktree.id]: tabs },
+    unifiedTabsByWorktree: {},
+    agentsVisibleHostIds: null,
+    agentsFilterRepoIds: []
+  })
+  return Object.keys(entries)
+}
+
+function queryWork(query: string) {
+  const texts = new Set([query, query.trim(), query.trim().toLowerCase()].filter(Boolean))
+  const originalBudget = clipboard.isClipboardTextByteLengthOverLimit
+  const originalTrim = String.prototype.trim
+  const originalLower = String.prototype.toLowerCase
+  const counts = { budget: 0, trim: 0, lower: 0 }
+  const budget = vi
+    .spyOn(clipboard, 'isClipboardTextByteLengthOverLimit')
+    .mockImplementation((text, maxBytes) => {
+      if (texts.has(text)) {
+        counts.budget += 1
+      }
+      return originalBudget(text, maxBytes)
+    })
+  const trim = vi.spyOn(String.prototype, 'trim').mockImplementation(function (this: string) {
+    if (texts.has(String(this))) {
+      counts.trim += 1
+    }
+    return originalTrim.call(this)
+  })
+  const lower = vi.spyOn(String.prototype, 'toLowerCase').mockImplementation(function (
+    this: string
+  ) {
+    if (texts.has(String(this))) {
+      counts.lower += 1
+    }
+    return originalLower.call(this)
+  })
+  return {
+    counts,
+    restore() {
+      budget.mockRestore()
+      trim.mockRestore()
+      lower.mockRestore()
+    }
+  }
+}
+
+function options(query: string): Parameters<typeof useAgentPaneThreads>[0] {
+  return { query, readFilter: 'all', groupBy: 'none', selectedPaneKey: null, showChildAgents: true }
+}
+
+describe('Activity search query work in the real hook', () => {
+  it.each([12, 128, 1000])('prepares one query for %i live threads', (count) => {
+    installThreads(count)
+    const work = queryWork(' PROJECT ☃ ')
+    const activity = renderHook(() => useAgentPaneThreads(options(' PROJECT ☃ ')))
+    work.restore()
+    expect(activity.result.current.allThreads).toHaveLength(count)
+    expect(activity.result.current.visibleThreads).toEqual(activity.result.current.allThreads)
+    for (const [index, thread] of activity.result.current.visibleThreads.entries()) {
+      expect(thread).toBe(activity.result.current.allThreads[index])
+    }
+    expect(work.counts).toEqual({ budget: 2, trim: 2, lower: 2 })
+  })
+
+  it.each(['', ' \t\n '])('keeps an empty query lazy: %j', (query) => {
+    installThreads(12)
+    const before = getThreadSearchTextComputeCount()
+    const activity = renderHook(() => useAgentPaneThreads(options(query)))
+    expect(activity.result.current.visibleThreads).toEqual(activity.result.current.allThreads)
+    expect(getThreadSearchTextComputeCount()).toBe(before)
+  })
+
+  it('retains both original and normalized UTF-8 byte limits', () => {
+    const query = 'İ'.repeat(700)
+    installThreads(12, query)
+    const before = getThreadSearchTextComputeCount()
+    const work = queryWork(query)
+    const activity = renderHook(() => useAgentPaneThreads(options(query)))
+    work.restore()
+    expect(activity.result.current.allThreads).toHaveLength(12)
+    expect(activity.result.current.visibleThreads).toEqual([])
+    expect(getThreadSearchTextComputeCount()).toBe(before)
+    expect(work.counts.budget).toBe(2)
+  })
+
+  it('does not prepare a row query before read/child/scope filters admit a row', () => {
+    const panes = installThreads(12)
+    useAppStore.setState({
+      acknowledgedAgentsByPaneKey: Object.fromEntries(panes.map((paneKey) => [paneKey, 100_000]))
+    })
+    const work = queryWork(' PROJECT ☃ ')
+    const activity = renderHook(() =>
+      useAgentPaneThreads({ ...options(' PROJECT ☃ '), readFilter: 'unread' })
+    )
+    work.restore()
+    expect(activity.result.current.allThreads).toHaveLength(12)
+    expect(activity.result.current.visibleThreads).toEqual([])
+    expect(work.counts).toEqual({ budget: 1, trim: 1, lower: 1 })
+  })
+
+  it('keeps selection, child classification and scoped row order', () => {
+    const panes = installThreads(8)
+    const parent = panes[0]
+    const child = panes[1]
+    useAppStore.setState({
+      runtimeAgentOrchestrationByPaneKey: {
+        [child]: { parentPaneKey: parent, taskId: 'task', dispatchId: 'dispatch' }
+      },
+      acknowledgedAgentsByPaneKey: { [child]: 100_000 }
+    })
+    const activity = renderHook((input) => useAgentPaneThreads(input), {
+      initialProps: {
+        ...options('PROJECT'),
+        readFilter: 'unread' as const,
+        showChildAgents: false,
+        selectedPaneKey: child
+      }
+    })
+    expect(activity.result.current.visibleThreads.map((thread) => thread.paneKey)).toEqual(panes)
+    act(() => useAppStore.setState({ agentsVisibleHostIds: [toSshExecutionHostId('other')] }))
+    expect(activity.result.current.visibleThreads.map((thread) => thread.paneKey)).toEqual([child])
+    activity.rerender({
+      ...options('NO MATCH'),
+      readFilter: 'unread',
+      showChildAgents: false,
+      selectedPaneKey: child
+    })
+    expect(activity.result.current.visibleThreads).toEqual([])
+    expect(activity.result.current.effectiveSelectedPaneKey).toBe(child)
+  })
+
+  it('uses a changed query and new thread data without a retained query cache', () => {
+    const panes = installThreads(12, 'first prompt')
+    const activity = renderHook((query) => useAgentPaneThreads(options(query)), {
+      initialProps: 'first'
+    })
+    expect(activity.result.current.visibleThreads).toHaveLength(12)
+    activity.rerender('second')
+    expect(activity.result.current.visibleThreads).toEqual([])
+    act(() => {
+      const entries = useAppStore.getState().agentStatusByPaneKey
+      useAppStore.setState({
+        agentStatusByPaneKey: {
+          ...entries,
+          [panes[2]]: { ...entries[panes[2]], prompt: 'second prompt' }
+        }
+      })
+    })
+    expect(activity.result.current.visibleThreads.map((thread) => thread.paneKey)).toEqual([
+      panes[2]
+    ])
+  })
+
+  it('keeps original oversized query rejection ahead of normalization/search', () => {
+    installThreads(12)
+    const query = ' '.repeat(2049)
+    const before = getThreadSearchTextComputeCount()
+    const work = queryWork(query)
+    const activity = renderHook(() => useAgentPaneThreads(options(query)))
+    work.restore()
+    expect(activity.result.current.visibleThreads).toEqual([])
+    expect(getThreadSearchTextComputeCount()).toBe(before)
+    expect(work.counts).toEqual({ budget: 1, trim: 0, lower: 0 })
+  })
+})
+
+describe('prepared Activity search preserves the public one-thread matcher', () => {
+  it('matches original output and lazy text for Unicode, boundary and empty queries', () => {
+    installThreads(8, 'Unicode İ 👩🏽‍💻 and BILLING')
+    const activity = renderHook(() => useAgentPaneThreads(options('')))
+    const queries = [
+      '',
+      '\t\n ',
+      'BILLING',
+      '  Unicode İ ',
+      '👩🏽‍💻',
+      '\ud800',
+      'x'.repeat(2048),
+      'é'.repeat(1024),
+      'é'.repeat(1025),
+      'İ'.repeat(700)
+    ]
+    for (const searchQuery of queries) {
+      const matches = createActivityThreadSearchMatcher(searchQuery)
+      expect(activity.result.current.allThreads.map(matches)).toEqual(
+        activity.result.current.allThreads.map((thread) =>
+          activityThreadMatchesSearchQuery({ thread, searchQuery })
+        )
+      )
+    }
+  })
+})
diff --git a/src/renderer/src/components/activity/activity-thread-grouping.ts b/src/renderer/src/components/activity/activity-thread-grouping.ts
index 79eef1b3688..17ad0bb447b 100644
--- a/src/renderer/src/components/activity/activity-thread-grouping.ts
+++ b/src/renderer/src/components/activity/activity-thread-grouping.ts
@@ -134,6 +134,20 @@ export function isActivitySearchQueryTooLarge(
   return isClipboardTextByteLengthOverLimit(query, maxBytes)
 }
 
+export function createActivityThreadSearchMatcher(
+  searchQuery: string
+): (thread: AgentPaneThread) => boolean {
+  if (isActivitySearchQueryTooLarge(searchQuery)) {
+    return () => false
+  }
+  const trimmedQuery = searchQuery.trim()
+  if (!trimmedQuery) {
+    return () => true
+  }
+  const normalizedQuery = trimmedQuery.toLowerCase()
+  return (thread) => threadSearchText(thread).includes(normalizedQuery)
+}
+
 export function activityThreadMatchesSearchQuery({
   thread,
   searchQuery
diff --git a/src/renderer/src/components/activity/use-agent-pane-threads.ts b/src/renderer/src/components/activity/use-agent-pane-threads.ts
index f9575f02a76..ce1f571cdbc 100644
--- a/src/renderer/src/components/activity/use-agent-pane-threads.ts
+++ b/src/renderer/src/components/activity/use-agent-pane-threads.ts
@@ -15,7 +15,7 @@ import { collectChildAgentPaneKeys } from './activity-thread-child-agent'
 const EMPTY_PANE_KEYS: ReadonlySet<string> = new Set()
 import { filterThreadsByActivityScope, resolveActivityScopeRepoIds } from './activity-scope-filter'
 import {
-  activityThreadMatchesSearchQuery,
+  createActivityThreadSearchMatcher,
   buildActivityThreadGroups,
   isActivitySearchQueryTooLarge
 } from './activity-thread-grouping'
@@ -212,6 +212,7 @@ export function useAgentPaneThreads(args: {
     const normalizedQuery = isActivitySearchQueryTooLarge(deferredQuery)
       ? null
       : deferredQuery.trim().toLowerCase()
+    let matchesSearchQuery: ReturnType<typeof createActivityThreadSearchMatcher> | undefined
     return scopeVisibleThreads.filter((thread) => {
       // Why: keep the just-selected thread visible after auto-mark-read flips it to read, else unread-only mode makes the clicked row vanish from the list.
       if (
@@ -232,7 +233,8 @@ export function useAgentPaneThreads(args: {
       if (normalizedQuery === null) {
         return false
       }
-      return activityThreadMatchesSearchQuery({ thread, searchQuery: normalizedQuery })
+      matchesSearchQuery ??= createActivityThreadSearchMatcher(normalizedQuery)
+      return matchesSearchQuery(thread)
     })
   }, [
     scopeVisibleThreads,