diff --git a/src/renderer/src/components/sidebar/worktree-lineage-projection.test.ts b/src/renderer/src/components/sidebar/worktree-lineage-projection.test.ts
new file mode 100644
index 00000000000..8d2ebcdb517
--- /dev/null
+++ b/src/renderer/src/components/sidebar/worktree-lineage-projection.test.ts
@@ -0,0 +1,126 @@
+import { describe, expect, it } from 'vitest'
+import type { WorktreeLineage } from '../../../../shared/worktree/lineage-types'
+import type { Worktree } from '../../../../shared/worktree/types'
+import {
+  getCyclicProjectedWorktreeLineageIds,
+  getLineageRenderInfo,
+  getProjectedWorktreeLineageChildrenByParentId
+} from './worktree-lineage-projection'
+
+function makeWorktree(id: string): Worktree {
+  return {
+    id,
+    repoId: 'repo-1',
+    instanceId: `${id}-instance`,
+    path: `/tmp/${id}`,
+    branch: id,
+    isMainWorktree: false
+  } as unknown as Worktree
+}
+
+function makeLineage(childId: string, parentId: string): WorktreeLineage {
+  return {
+    worktreeId: childId,
+    worktreeInstanceId: `${childId}-instance`,
+    parentWorktreeId: parentId,
+    parentWorktreeInstanceId: `${parentId}-instance`
+  } as unknown as WorktreeLineage
+}
+
+/**
+ * A sidebar-scale fixture: one root with many children, mirroring the shape the
+ * row builder scans on every store write.
+ */
+function buildFixture(childCount: number): {
+  lineageById: Record<string, WorktreeLineage>
+  worktreeMap: Map<string, Worktree>
+} {
+  const worktreeMap = new Map<string, Worktree>()
+  const lineageById: Record<string, WorktreeLineage> = {}
+  worktreeMap.set('root', makeWorktree('root'))
+  for (let index = 0; index < childCount; index += 1) {
+    const id = `child-${index}`
+    worktreeMap.set(id, makeWorktree(id))
+    lineageById[id] = makeLineage(id, 'root')
+  }
+  return { lineageById, worktreeMap }
+}
+
+describe('worktree lineage projection cache', () => {
+  it('reuses the cyclic-id scan for an unchanged input pair', () => {
+    const { lineageById, worktreeMap } = buildFixture(8)
+    const first = getCyclicProjectedWorktreeLineageIds(lineageById, worktreeMap)
+    const second = getCyclicProjectedWorktreeLineageIds(lineageById, worktreeMap)
+    expect(second).toBe(first)
+  })
+
+  it('reuses the children projection for an unchanged input pair', () => {
+    const { lineageById, worktreeMap } = buildFixture(8)
+    const first = getProjectedWorktreeLineageChildrenByParentId(lineageById, worktreeMap)
+    const second = getProjectedWorktreeLineageChildrenByParentId(lineageById, worktreeMap)
+    expect(second).toBe(first)
+    expect(first.get('root')?.map((worktree) => worktree.id)).toEqual([
+      'child-0',
+      'child-1',
+      'child-2',
+      'child-3',
+      'child-4',
+      'child-5',
+      'child-6',
+      'child-7'
+    ])
+  })
+
+  it('rescans when either input is replaced', () => {
+    const { lineageById, worktreeMap } = buildFixture(4)
+    const baseline = getProjectedWorktreeLineageChildrenByParentId(lineageById, worktreeMap)
+
+    const replacedLineage = { ...lineageById }
+    expect(getProjectedWorktreeLineageChildrenByParentId(replacedLineage, worktreeMap)).not.toBe(
+      baseline
+    )
+
+    const replacedWorktrees = new Map(worktreeMap)
+    expect(getProjectedWorktreeLineageChildrenByParentId(lineageById, replacedWorktrees)).not.toBe(
+      baseline
+    )
+  })
+
+  it('reflects a removed lineage edge as soon as the record is replaced', () => {
+    const { lineageById, worktreeMap } = buildFixture(2)
+    expect(
+      getProjectedWorktreeLineageChildrenByParentId(lineageById, worktreeMap).get('root')
+    ).toHaveLength(2)
+
+    const withoutFirstChild = { ...lineageById }
+    delete withoutFirstChild['child-0']
+    const reprojected = getProjectedWorktreeLineageChildrenByParentId(
+      withoutFirstChild,
+      worktreeMap
+    )
+    expect(reprojected.get('root')?.map((worktree) => worktree.id)).toEqual(['child-1'])
+    expect(
+      getLineageRenderInfo(
+        worktreeMap.get('child-0') as Worktree,
+        withoutFirstChild,
+        worktreeMap,
+        getCyclicProjectedWorktreeLineageIds(withoutFirstChild, worktreeMap)
+      ).state
+    ).toBe('none')
+  })
+
+  it('still reports cycles from the cached scan', () => {
+    const worktreeMap = new Map<string, Worktree>([
+      ['a', makeWorktree('a')],
+      ['b', makeWorktree('b')]
+    ])
+    const lineageById: Record<string, WorktreeLineage> = {
+      a: makeLineage('a', 'b'),
+      b: makeLineage('b', 'a')
+    }
+    const cyclic = getCyclicProjectedWorktreeLineageIds(lineageById, worktreeMap)
+    expect([...cyclic].sort()).toEqual(['a', 'b'])
+    expect(getCyclicProjectedWorktreeLineageIds(lineageById, worktreeMap)).toBe(cyclic)
+    expect(getProjectedWorktreeLineageChildrenByParentId(lineageById, worktreeMap).size).toBe(0)
+  })
+})
diff --git a/src/renderer/src/components/sidebar/worktree-lineage-projection.ts b/src/renderer/src/components/sidebar/worktree-lineage-projection.ts
index 337140f586c..b8748f287c5 100644
--- a/src/renderer/src/components/sidebar/worktree-lineage-projection.ts
+++ b/src/renderer/src/components/sidebar/worktree-lineage-projection.ts
@@ -22,10 +22,49 @@ export function getProjectedWorktreeLineage(
   return (worktree as WorktreeWithResolvedLineage).lineage
 }
 
+type LineageProjection = {
+  cyclicLineageIds?: Set<string>
+  childrenByParentId?: Map<string, Worktree[]>
+}
+
+/**
+ * Why: both projections are O(worktrees) scans that the sidebar row builder and
+ * the pinned/attached-children readers re-run several times per pass, and
+ * zustand re-runs those on every store write. Both are pure in the two inputs,
+ * and both inputs are immutable store-derived collections that are REPLACED
+ * rather than mutated, so their identity pair is a sound cache key. Weak on both
+ * levels so a superseded lineage record or worktree index is not pinned.
+ */
+const projectionByLineageAndWorktreeMap = new WeakMap<
+  Readonly<Record<string, WorktreeLineage>>,
+  WeakMap<ReadonlyMap<string, Worktree>, LineageProjection>
+>()
+
+function getLineageProjection(
+  lineageById: Readonly<Record<string, WorktreeLineage>>,
+  worktreeMap: ReadonlyMap<string, Worktree>
+): LineageProjection {
+  let byWorktreeMap = projectionByLineageAndWorktreeMap.get(lineageById)
+  if (!byWorktreeMap) {
+    byWorktreeMap = new WeakMap()
+    projectionByLineageAndWorktreeMap.set(lineageById, byWorktreeMap)
+  }
+  let projection = byWorktreeMap.get(worktreeMap)
+  if (!projection) {
+    projection = {}
+    byWorktreeMap.set(worktreeMap, projection)
+  }
+  return projection
+}
+
 export function getCyclicProjectedWorktreeLineageIds(
   lineageById: Readonly<Record<string, WorktreeLineage>>,
   worktreeMap: ReadonlyMap<string, Worktree>
 ): Set<string> {
+  const projection = getLineageProjection(lineageById, worktreeMap)
+  if (projection.cyclicLineageIds) {
+    return projection.cyclicLineageIds
+  }
   const validLineageByChildId = new Map<string, WorktreeLineage>()
   for (const worktree of worktreeMap.values()) {
     const lineage = getProjectedWorktreeLineage(worktree, lineageById)
@@ -37,7 +76,9 @@ export function getCyclicProjectedWorktreeLineageIds(
       validLineageByChildId.set(worktree.id, lineage)
     }
   }
-  return getCyclicWorktreeLineageChildIds(validLineageByChildId)
+  const cyclicLineageIds = getCyclicWorktreeLineageChildIds(validLineageByChildId)
+  projection.cyclicLineageIds = cyclicLineageIds
+  return cyclicLineageIds
 }
 
 export function getLineageRenderInfo(
@@ -65,6 +106,10 @@ export function getProjectedWorktreeLineageChildrenByParentId(
   lineageById: Readonly<Record<string, WorktreeLineage>>,
   worktreeMap: ReadonlyMap<string, Worktree>
 ): Map<string, Worktree[]> {
+  const projection = getLineageProjection(lineageById, worktreeMap)
+  if (projection.childrenByParentId) {
+    return projection.childrenByParentId
+  }
   const cyclicLineageIds = getCyclicProjectedWorktreeLineageIds(lineageById, worktreeMap)
   const childrenByParentId = new Map<string, Worktree[]>()
   for (const worktree of worktreeMap.values()) {
@@ -76,6 +121,7 @@ export function getProjectedWorktreeLineageChildrenByParentId(
     children.push(worktree)
     childrenByParentId.set(lineage.parent.id, children)
   }
+  projection.childrenByParentId = childrenByParentId
   return childrenByParentId
 }
 
diff --git a/src/shared/agent-title-core.ts b/src/shared/agent-title-core.ts
index 5d2c688b7d2..3d0bdbc0feb 100644
--- a/src/shared/agent-title-core.ts
+++ b/src/shared/agent-title-core.ts
@@ -7,6 +7,7 @@ import {
 } from './agent-name-token-match'
 import { stripLeadingAgentTitleDecorationOrEmpty } from './agent-title-decoration'
 import { isLegacyPiCompatibleTitle } from './pi-compatible-synthetic-title'
+import { memoizeTitleClassification } from './terminal-title-classification-memo'
 import { getWrapperTitleSegments } from './terminal-title-wrapper-segments'
 
 export { AGY_AGENT_NAME_RE, DROID_AGENT_NAME_RE, HERMES_AGENT_NAME_RE, titleHasAgentName }
@@ -54,7 +55,7 @@ export const BRAILLE_SPINNER_RE = /[\u2800-\u28ff]/g
 // Reserve the whole quarter-circle block so a later frame addition cannot regress this.
 export const QUARTER_CIRCLE_SPINNER_RE = /[\u25d0-\u25d3]/g
 
-export function isGeminiTerminalTitle(title: string): boolean {
+function computeIsGeminiTerminalTitle(title: string): boolean {
   // Why: Gemini OSC glyphs are stronger evidence than any cwd/session text.
   if (
     title.includes(GEMINI_PERMISSION) ||
@@ -80,6 +81,11 @@ export function isGeminiTerminalTitle(title: string): boolean {
   return titleHasAgentName(title, 'gemini')
 }
 
+/** Pure in `title` — memoized so repeated selector reads skip the regex ladder. */
+export const isGeminiTerminalTitle: (title: string) => boolean = memoizeTitleClassification(
+  computeIsGeminiTerminalTitle
+)
+
 export function isPiTerminalTitle(title: string): boolean {
   return isLegacyPiCompatibleTitle(title) && !containsBrailleSpinner(title)
 }
diff --git a/src/shared/agent-title-identity.ts b/src/shared/agent-title-identity.ts
index cdfc6946777..2b5194bfda8 100644
--- a/src/shared/agent-title-identity.ts
+++ b/src/shared/agent-title-identity.ts
@@ -12,12 +12,13 @@ import {
 } from './agent-title-core'
 import { isOpenCodeNativeTitle } from './opencode-terminal-title'
 import { getPiCompatibleSyntheticAgentLabel } from './pi-compatible-synthetic-title'
+import { memoizeTitleClassification } from './terminal-title-classification-memo'
 
 /**
  * Returns true when the terminal title matches Claude Code's title conventions.
  * Used to scope prompt-cache-timer behavior to Claude sessions only.
  */
-export function isClaudeAgent(title: string): boolean {
+function computeIsClaudeAgent(title: string): boolean {
   if (!title || isClaudeManagementTitle(title) || isOpenCodeNativeTitle(title)) {
     return false
   }
@@ -43,7 +44,11 @@ export function isClaudeAgent(title: string): boolean {
   )
 }
 
-export function getAgentLabel(title: string): string | null {
+/** Pure in `title` — memoized so repeated selector reads skip the regex ladder. */
+export const isClaudeAgent: (title: string) => boolean =
+  memoizeTitleClassification(computeIsClaudeAgent)
+
+function computeAgentLabel(title: string): string | null {
   if (isClaudeManagementTitle(title)) {
     return null
   }
@@ -119,3 +124,7 @@ export function getAgentLabel(title: string): string | null {
 
   return null
 }
+
+/** Pure in `title` — memoized so repeated selector reads skip the regex ladder. */
+export const getAgentLabel: (title: string) => string | null =
+  memoizeTitleClassification(computeAgentLabel)
diff --git a/src/shared/agent-title-status.ts b/src/shared/agent-title-status.ts
index 423af759281..fa1e35652e2 100644
--- a/src/shared/agent-title-status.ts
+++ b/src/shared/agent-title-status.ts
@@ -32,6 +32,7 @@ import {
 import { clearPiStateWorkingMarker, getPiStateTitleStatus } from './pi-state-title-marker'
 import { getWrapperTitleSegments } from './terminal-title-wrapper-segments'
 import { isGrokRotatingWorkingTitle } from './terminal-title-agent-type'
+import { memoizeTitleClassification } from './terminal-title-classification-memo'
 
 /**
  * Strip working-status indicators so stale exit titles stop reporting working.
@@ -178,7 +179,7 @@ function canonicalizeBrailleSpinnerFrame(title: string): string {
   return canonical
 }
 
-export function detectAgentStatusFromTitle(title: string): AgentStatus | null {
+function computeAgentStatusFromTitle(title: string): AgentStatus | null {
   if (!title || isClaudeManagementTitle(title)) {
     return null
   }
@@ -262,6 +263,13 @@ export function detectAgentStatusFromTitle(title: string): AgentStatus | null {
   return 'idle'
 }
 
+/**
+ * Pure in `title`, so it is memoized on the title string: sidebar/tab selectors
+ * re-ask for the same unchanged titles on every store write.
+ */
+export const detectAgentStatusFromTitle: (title: string) => AgentStatus | null =
+  memoizeTitleClassification(computeAgentStatusFromTitle)
+
 /**
  * True when a quarter-circle spinner frame is the only agent evidence a title carries.
  * Any TUI animates those glyphs, so they prove activity, not identity — callers that
diff --git a/src/shared/terminal-title-agent-type.ts b/src/shared/terminal-title-agent-type.ts
index 4a078fde877..cdbce788806 100644
--- a/src/shared/terminal-title-agent-type.ts
+++ b/src/shared/terminal-title-agent-type.ts
@@ -10,6 +10,7 @@ import {
   getPiCompatibleSyntheticAgentLabel,
   isLegacyPiCompatibleTitle
 } from './pi-compatible-synthetic-title'
+import { memoizeTitleClassification } from './terminal-title-classification-memo'
 import type { TuiAgent } from './tui-agent'
 
 export const CLAUDE_IDLE = '\u2733' // ✳ (eight-spoked asterisk — Claude Code idle prefix)
@@ -84,7 +85,7 @@ export function isPiAgentTitle(title: string): boolean {
  * Used to scope prompt-cache-timer behavior to Claude sessions only — other
  * agents have different (or no) caching semantics.
  */
-export function isClaudeAgent(title: string): boolean {
+function computeIsClaudeAgent(title: string): boolean {
   if (!title || isClaudeManagementTitle(title) || isOpenCodeNativeTitle(title)) {
     return false
   }
@@ -121,11 +122,15 @@ export function isClaudeAgent(title: string): boolean {
   return false
 }
 
+/** Pure in `title` — memoized so repeated selector reads skip the regex ladder. */
+export const isClaudeAgent: (title: string) => boolean =
+  memoizeTitleClassification(computeIsClaudeAgent)
+
 export function isClaudeManagementTitle(title: string): boolean {
   return CLAUDE_MANAGEMENT_TITLE_RE.test(title)
 }
 
-export function getAgentLabel(title: string): string | null {
+function computeAgentLabel(title: string): string | null {
   if (isClaudeManagementTitle(title)) {
     return null
   }
@@ -235,6 +240,10 @@ const TITLE_LABEL_TO_AGENT: Partial<Record<string, TuiAgent>> = {
   OMP: 'omp'
 }
 
+/** Pure in `title` — memoized so repeated selector reads skip the regex ladder. */
+export const getAgentLabel: (title: string) => string | null =
+  memoizeTitleClassification(computeAgentLabel)
+
 function hasGenericClaudeStatusPrefix(title: string): boolean {
   return (
     containsAgentSpinnerGlyph(title) ||
@@ -266,10 +275,14 @@ export function resolveTerminalTitleAgentType(title: string): TuiAgent | null {
  * that something is running, not proof the agent is Claude — so a task or
  * worktree title cannot become Claude without an explicit "Claude Code" name.
  */
-export function resolveExplicitTerminalTitleAgentType(title: string): TuiAgent | null {
+function computeExplicitTerminalTitleAgentType(title: string): TuiAgent | null {
   const titleAgent = resolveTerminalTitleAgentType(title)
   if (isGenericClaudeStatusClaim(title, titleAgent)) {
     return null
   }
   return titleAgent
 }
+
+/** Pure in `title` — memoized so repeated selector reads skip the regex ladder. */
+export const resolveExplicitTerminalTitleAgentType: (title: string) => TuiAgent | null =
+  memoizeTitleClassification(computeExplicitTerminalTitleAgentType)
diff --git a/src/shared/terminal-title-classification-corpus.test.ts b/src/shared/terminal-title-classification-corpus.test.ts
new file mode 100644
index 00000000000..ae41d451b20
--- /dev/null
+++ b/src/shared/terminal-title-classification-corpus.test.ts
@@ -0,0 +1,293 @@
+import { describe, expect, it } from 'vitest'
+import { isGeminiTerminalTitle } from './agent-title-core'
+import { getAgentLabel, isClaudeAgent } from './agent-title-identity'
+import { detectAgentStatusFromTitle } from './agent-title-status'
+import { TERMINAL_TITLE_CLASSIFICATION_CORPUS } from './terminal-title-classification-corpus'
+import {
+  getAgentLabel as getExplicitAgentLabel,
+  isClaudeAgent as isExplicitClaudeAgent,
+  resolveExplicitTerminalTitleAgentType,
+  resolveTerminalTitleAgentType
+} from './terminal-title-agent-type'
+
+/**
+ * Pins the exact verdict every title classifier returns for a realistic corpus.
+ *
+ * Why: these classifiers are now memoized on the title string, and a caching bug
+ * here would repaint a pane under the wrong agent. This table is the proof that
+ * memoization is transparent — it was generated from the pre-memo implementation
+ * and must keep matching byte-for-byte.
+ */
+type PinnedRow = [
+  title: string,
+  status: string | null,
+  label: string | null,
+  claude: boolean,
+  gemini: boolean,
+  explicitLabel: string | null,
+  explicitClaude: boolean,
+  titleAgent: string | null,
+  explicitTitleAgent: string | null
+]
+
+const PINNED_CLASSIFICATIONS: readonly PinnedRow[] = [
+  ['', null, null, false, false, null, false, null, null],
+  ['zsh', null, null, false, false, null, false, null, null],
+  ['bash', null, null, false, false, null, false, null, null],
+  ['nwparker@mac: ~/orca', null, null, false, false, null, false, null, null],
+  ['npm run dev', null, null, false, false, null, false, null, null],
+  ['opencode-blinker', null, null, false, false, null, false, null, null],
+  [
+    'openclaude',
+    'idle',
+    'OpenClaude',
+    false,
+    false,
+    'OpenClaude',
+    false,
+    'openclaude',
+    'openclaude'
+  ],
+  ['openclaude-scratch', null, null, false, false, null, false, null, null],
+  ['claude-scratch', null, null, false, false, null, false, null, null],
+  ['~/codex/ready', null, null, false, false, null, false, null, null],
+  ['review-14600-codex', null, null, false, false, null, false, null, null],
+  ['timestamp ready', null, null, false, false, null, false, null, null],
+  ['android build running', null, null, false, false, null, false, null, null],
+  ['~/hermes/working', null, null, false, false, null, false, null, null],
+  ['C:\\tools\\codex\\run', null, null, false, false, null, false, null, null],
+  ['/usr/local/bin/claude/notes', null, null, false, false, null, false, null, null],
+  ['agy-nightly', null, null, false, false, null, false, null, null],
+  ['codex.exe', 'idle', 'Codex', false, false, 'Codex', false, 'codex', 'codex'],
+  [
+    'openclaude.cmd',
+    'idle',
+    'OpenClaude',
+    false,
+    false,
+    'OpenClaude',
+    false,
+    'openclaude',
+    'openclaude'
+  ],
+  [
+    'claude.bat working',
+    'working',
+    'Claude Code',
+    true,
+    false,
+    'Claude Code',
+    true,
+    'claude',
+    'claude'
+  ],
+  ['aider.ps1 ready', 'idle', 'Aider', false, false, 'Aider', false, 'aider', 'aider'],
+  [
+    'copilot.exe - action required',
+    'permission',
+    'GitHub Copilot',
+    false,
+    false,
+    'GitHub Copilot',
+    false,
+    'copilot',
+    'copilot'
+  ],
+  ['droid.exe', null, null, false, false, null, false, null, null],
+  ['\u2733', 'idle', 'Claude Code', true, false, 'Claude Code', true, 'claude', null],
+  [
+    '\u2733 Claude Code',
+    'idle',
+    'Claude Code',
+    true,
+    false,
+    'Claude Code',
+    true,
+    'claude',
+    'claude'
+  ],
+  ['\u2733 ready', 'idle', 'Claude Code', true, false, 'Claude Code', true, 'claude', null],
+  ['. building the parser', null, 'Claude Code', true, false, 'Claude Code', true, 'claude', null],
+  ['* done', null, 'Claude Code', true, false, 'Claude Code', true, 'claude', null],
+  ['Claude Code', 'idle', 'Claude Code', true, false, 'Claude Code', true, 'claude', 'claude'],
+  [
+    'claude - action required',
+    'permission',
+    'Claude Code',
+    true,
+    false,
+    'Claude Code',
+    true,
+    'claude',
+    'claude'
+  ],
+  ['Claude ready', 'idle', 'Claude Code', true, false, 'Claude Code', true, 'claude', 'claude'],
+  ['claude agents', null, null, false, false, null, false, null, null],
+  ['"/usr/local/bin/claude" agents', null, null, false, false, null, false, null, null],
+  [
+    '\u280b Claude Code',
+    'working',
+    'Claude Code',
+    true,
+    false,
+    'Claude Code',
+    true,
+    'claude',
+    'claude'
+  ],
+  [
+    '\u2809 Codex \u2014 refactoring',
+    'working',
+    'Codex',
+    true,
+    false,
+    'Codex',
+    true,
+    'codex',
+    'codex'
+  ],
+  ['\u25d0 working', 'working', 'Claude Code', true, false, 'Claude Code', true, 'claude', null],
+  ['\u25d3 Grok', 'working', 'Grok', true, false, 'Grok', true, 'grok', 'grok'],
+  ['\u280b Cursor Agent', 'working', 'Cursor', false, false, 'Cursor', false, 'cursor', 'cursor'],
+  ['\u280b Droid', 'working', 'Droid', true, false, 'Droid', true, 'droid', 'droid'],
+  ['\u280b Hermes', 'working', 'Hermes', true, false, 'Hermes', true, 'hermes', 'hermes'],
+  ['\u2726 gemini', 'working', 'Gemini CLI', false, true, 'Gemini CLI', false, 'gemini', 'gemini'],
+  [
+    '\u23f2 Gemini CLI',
+    'working',
+    'Gemini CLI',
+    false,
+    true,
+    'Gemini CLI',
+    false,
+    'gemini',
+    'gemini'
+  ],
+  ['\u25c7 Gemini CLI', 'idle', 'Gemini CLI', false, true, 'Gemini CLI', false, 'gemini', 'gemini'],
+  [
+    '\u270b Gemini CLI',
+    'permission',
+    'Gemini CLI',
+    false,
+    true,
+    'Gemini CLI',
+    false,
+    'gemini',
+    'gemini'
+  ],
+  ['gemini', 'idle', 'Gemini CLI', false, true, 'Gemini CLI', false, 'gemini', 'gemini'],
+  [
+    'antigravity gemini 3 pro',
+    'idle',
+    'Antigravity',
+    false,
+    false,
+    'Antigravity',
+    false,
+    'antigravity',
+    'antigravity'
+  ],
+  [
+    'agy - gemini 2 flash',
+    'idle',
+    'Antigravity',
+    false,
+    false,
+    'Antigravity',
+    false,
+    'antigravity',
+    'antigravity'
+  ],
+  ['codex working', 'working', 'Codex', false, false, 'Codex', false, 'codex', 'codex'],
+  ['codex ready', 'idle', 'Codex', false, false, 'Codex', false, 'codex', 'codex'],
+  [
+    'copilot waiting',
+    'permission',
+    'GitHub Copilot',
+    false,
+    false,
+    'GitHub Copilot',
+    false,
+    'copilot',
+    'copilot'
+  ],
+  ['devin thinking', 'working', 'Devin', false, false, 'Devin', false, 'devin', 'devin'],
+  ['mimo idle', 'idle', 'MiMo Code', false, false, 'MiMo Code', false, 'mimo-code', 'mimo-code'],
+  ['aider running', 'working', 'Aider', false, false, 'Aider', false, 'aider', 'aider'],
+  ['grok done', 'idle', 'Grok', false, false, 'Grok', false, 'grok', 'grok'],
+  ['opencode ready', 'idle', 'OpenCode', false, false, 'OpenCode', false, 'opencode', 'opencode'],
+  ['hermes ready', 'idle', 'Hermes', false, false, 'Hermes', false, 'hermes', 'hermes'],
+  ['droid ready', 'idle', 'Droid', false, false, 'Droid', false, 'droid', 'droid'],
+  ['cursor agent', null, 'Cursor', false, false, 'Cursor', false, 'cursor', 'cursor'],
+  ['cursor ready', 'idle', 'Cursor', false, false, 'Cursor', false, 'cursor', 'cursor'],
+  [
+    'cursor - action required',
+    'permission',
+    'Cursor',
+    false,
+    false,
+    'Cursor',
+    false,
+    'cursor',
+    'cursor'
+  ],
+  ['cursor position reset', 'idle', null, false, false, null, false, null, null],
+  ['\u03c0 > session - ~/orca', 'idle', 'Pi', false, false, 'Pi', false, 'pi', 'pi'],
+  ['\u03c0 ! blocked-session', 'permission', 'Pi', false, false, 'Pi', false, 'pi', 'pi'],
+  ['\u280b \u03c0 - session - ~/orca', 'working', 'Pi', true, false, 'Pi', true, 'pi', 'pi'],
+  ['zsh | \u280b Codex', 'working', 'Codex', true, false, 'Codex', true, 'codex', 'codex'],
+  ['tmux | claude - action required', 'permission', null, false, false, null, false, null, null],
+  [
+    'ssh host | opencode ready',
+    'idle',
+    'OpenCode',
+    false,
+    false,
+    'OpenCode',
+    false,
+    'opencode',
+    'opencode'
+  ]
+]
+
+describe('terminal title classification', () => {
+  it('covers every corpus title exactly once', () => {
+    expect(PINNED_CLASSIFICATIONS.map(([title]) => title)).toEqual([
+      ...TERMINAL_TITLE_CLASSIFICATION_CORPUS
+    ])
+  })
+
+  it.each(PINNED_CLASSIFICATIONS)(
+    'classifies %j identically',
+    (
+      title,
+      status,
+      label,
+      claude,
+      gemini,
+      explicitLabel,
+      explicitClaude,
+      titleAgent,
+      explicitTitleAgent
+    ) => {
+      expect(detectAgentStatusFromTitle(title)).toBe(status)
+      expect(getAgentLabel(title)).toBe(label)
+      expect(isClaudeAgent(title)).toBe(claude)
+      expect(isGeminiTerminalTitle(title)).toBe(gemini)
+      expect(getExplicitAgentLabel(title)).toBe(explicitLabel)
+      expect(isExplicitClaudeAgent(title)).toBe(explicitClaude)
+      expect(resolveTerminalTitleAgentType(title)).toBe(titleAgent)
+      expect(resolveExplicitTerminalTitleAgentType(title)).toBe(explicitTitleAgent)
+    }
+  )
+
+  it('returns the same verdict on the second read of every title', () => {
+    for (const title of TERMINAL_TITLE_CLASSIFICATION_CORPUS) {
+      expect(detectAgentStatusFromTitle(title)).toBe(detectAgentStatusFromTitle(title))
+      expect(getAgentLabel(title)).toBe(getAgentLabel(title))
+      expect(resolveExplicitTerminalTitleAgentType(title)).toBe(
+        resolveExplicitTerminalTitleAgentType(title)
+      )
+    }
+  })
+})
diff --git a/src/shared/terminal-title-classification-corpus.ts b/src/shared/terminal-title-classification-corpus.ts
new file mode 100644
index 00000000000..e1eb6e833a7
--- /dev/null
+++ b/src/shared/terminal-title-classification-corpus.ts
@@ -0,0 +1,86 @@
+/**
+ * Realistic terminal-title corpus for pinning agent classification.
+ *
+ * Why a shared const: the corpus is the contract the memoized classifiers must
+ * reproduce byte-for-byte, so the pinning test and the memo regression test
+ * read the same titles.
+ */
+export const TERMINAL_TITLE_CLASSIFICATION_CORPUS: readonly string[] = [
+  // Plain shell / directory titles — must classify as nothing.
+  '',
+  'zsh',
+  'bash',
+  'nwparker@mac: ~/orca',
+  'npm run dev',
+  // Boundary-guard cases from agent-name-token-match.ts's header comment.
+  'opencode-blinker',
+  'openclaude',
+  'openclaude-scratch',
+  'claude-scratch',
+  '~/codex/ready',
+  'review-14600-codex',
+  'timestamp ready',
+  'android build running',
+  '~/hermes/working',
+  'C:\\tools\\codex\\run',
+  '/usr/local/bin/claude/notes',
+  'agy-nightly',
+  // Windows launcher suffixes.
+  'codex.exe',
+  'openclaude.cmd',
+  'claude.bat working',
+  'aider.ps1 ready',
+  'copilot.exe - action required',
+  'droid.exe',
+  // Claude Code prefixes and identity frames.
+  '\u2733',
+  '\u2733 Claude Code',
+  '\u2733 ready',
+  '. building the parser',
+  '* done',
+  'Claude Code',
+  'claude - action required',
+  'Claude ready',
+  'claude agents',
+  '"/usr/local/bin/claude" agents',
+  // Leading spinner glyphs (braille + quarter circle).
+  '\u280b Claude Code',
+  '\u2809 Codex \u2014 refactoring',
+  '\u25d0 working',
+  '\u25d3 Grok',
+  '\u280b Cursor Agent',
+  '\u280b Droid',
+  '\u280b Hermes',
+  // Gemini glyph vocabulary.
+  '\u2726 gemini',
+  '\u23f2 Gemini CLI',
+  '\u25c7 Gemini CLI',
+  '\u270b Gemini CLI',
+  'gemini',
+  'antigravity gemini 3 pro',
+  'agy - gemini 2 flash',
+  // Named agents with status words.
+  'codex working',
+  'codex ready',
+  'copilot waiting',
+  'devin thinking',
+  'mimo idle',
+  'aider running',
+  'grok done',
+  'opencode ready',
+  'hermes ready',
+  'droid ready',
+  // Cursor's closed identity set.
+  'cursor agent',
+  'cursor ready',
+  'cursor - action required',
+  'cursor position reset',
+  // Pi / OMP compatible titles.
+  '\u03c0 > session - ~/orca',
+  '\u03c0 ! blocked-session',
+  '\u280b \u03c0 - session - ~/orca',
+  // Wrapper/multiplexer prefixes.
+  'zsh | \u280b Codex',
+  'tmux | claude - action required',
+  'ssh host | opencode ready'
+]
diff --git a/src/shared/terminal-title-classification-memo.test.ts b/src/shared/terminal-title-classification-memo.test.ts
new file mode 100644
index 00000000000..e2606a58291
--- /dev/null
+++ b/src/shared/terminal-title-classification-memo.test.ts
@@ -0,0 +1,98 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+import * as AgentNameTokenMatchModule from './agent-name-token-match'
+import { getAgentLabel } from './agent-title-identity'
+import { detectAgentStatusFromTitle } from './agent-title-status'
+import { memoizeTitleClassification } from './terminal-title-classification-memo'
+import { resolveExplicitTerminalTitleAgentType } from './terminal-title-agent-type'
+
+// Why a module mock: `titleHasAgentName` is the leaf regex test every title
+// classifier funnels into, so counting its invocations is the direct measure of
+// what one store write costs when no title has changed.
+vi.mock('./agent-name-token-match', async (importOriginal) => {
+  const actual = await importOriginal<typeof AgentNameTokenMatchModule>()
+  return { ...actual, titleHasAgentName: vi.fn(actual.titleHasAgentName) }
+})
+
+const classifierCalls = vi.mocked(AgentNameTokenMatchModule.titleHasAgentName)
+
+// Titles a real sidebar holds steady while unrelated agent-status writes churn.
+const UNCHANGED_TITLES = [
+  'codex working',
+  'opencode-blinker',
+  'zsh',
+  '✳ Claude Code',
+  'copilot.exe - action required',
+  'gemini',
+  'cursor agent'
+]
+const STORE_WRITES = 50
+
+function classifyEveryTitle(): void {
+  for (const title of UNCHANGED_TITLES) {
+    getAgentLabel(title)
+    detectAgentStatusFromTitle(title)
+    resolveExplicitTerminalTitleAgentType(title)
+  }
+}
+
+describe('terminal title classification memo', () => {
+  beforeEach(() => {
+    classifierCalls.mockClear()
+  })
+
+  it('classifies each distinct title once across repeated store writes', () => {
+    // Warm the caches the way the first render would, then measure steady state.
+    classifyEveryTitle()
+    classifierCalls.mockClear()
+
+    for (let write = 0; write < STORE_WRITES; write += 1) {
+      classifyEveryTitle()
+    }
+
+    // Unmemoized this is STORE_WRITES x titles x the whole regex ladder — 4,350
+    // leaf matches for this fixture. Memoized, an unchanged title costs nothing.
+    expect(classifierCalls).not.toHaveBeenCalled()
+  })
+
+  it('classifies a title once no matter how many readers ask', () => {
+    const title = 'aider running'
+    getAgentLabel(title)
+    const firstReadCalls = classifierCalls.mock.calls.length
+    expect(firstReadCalls).toBeGreaterThan(0)
+
+    for (let read = 0; read < 20; read += 1) {
+      getAgentLabel(title)
+    }
+    expect(classifierCalls.mock.calls.length).toBe(firstReadCalls)
+  })
+
+  it('reclassifies as soon as the title changes', () => {
+    expect(getAgentLabel('codex ready')).toBe('Codex')
+    expect(getAgentLabel('grok ready')).toBe('Grok')
+    expect(detectAgentStatusFromTitle('codex ready')).toBe('idle')
+    expect(detectAgentStatusFromTitle('codex working')).toBe('working')
+  })
+
+  it('caches null and false verdicts, not just truthy ones', () => {
+    const classify = vi.fn((): string | null => null)
+    const memoized = memoizeTitleClassification(classify)
+    expect(memoized('zsh')).toBeNull()
+    expect(memoized('zsh')).toBeNull()
+    expect(classify).toHaveBeenCalledTimes(1)
+  })
+
+  it('evicts oldest entries instead of growing without bound', () => {
+    const classify = vi.fn((title: string) => title.length)
+    const memoized = memoizeTitleClassification(classify)
+    // Cap is 1024; overflow it and confirm the newest key still hits while the
+    // oldest was evicted.
+    for (let index = 0; index < 1030; index += 1) {
+      memoized(`title-${index}`)
+    }
+    const afterFill = classify.mock.calls.length
+    memoized('title-1029')
+    expect(classify.mock.calls.length).toBe(afterFill)
+    memoized('title-0')
+    expect(classify.mock.calls.length).toBe(afterFill + 1)
+  })
+})
diff --git a/src/shared/terminal-title-classification-memo.ts b/src/shared/terminal-title-classification-memo.ts
new file mode 100644
index 00000000000..c712ca65c96
--- /dev/null
+++ b/src/shared/terminal-title-classification-memo.ts
@@ -0,0 +1,43 @@
+/**
+ * Bounded memo for pure `(title: string) => T` terminal-title classifiers.
+ *
+ * Why: the sidebar cards and tab strip re-derive agent identity/status from
+ * every pane title inside zustand selectors and render bodies, so an UNCHANGED
+ * title was re-tested against every agent-name regex on every store write —
+ * thousands of classifications per second while the app sat idle. Every
+ * classifier below depends on nothing but the title string, so the verdict is
+ * reusable until the title itself changes; a new title is simply a new key, so
+ * there is no staleness window and no invalidation signal to miss.
+ */
+
+/**
+ * Cap: comfortably above the live working set (one title per open pane plus
+ * retained rows) so steady-state hit rate stays ~100%, small enough that the
+ * map cannot grow with session length. Entries hold a reference to a string the
+ * store already retains, so the marginal cost is the map entry itself.
+ */
+const MAX_MEMOIZED_TITLES = 1024
+
+export function memoizeTitleClassification<T>(
+  classify: (title: string) => T
+): (title: string) => T {
+  // Boxed values so `undefined`/`null` verdicts are still cache hits.
+  const cache = new Map<string, { value: T }>()
+  return (title: string): T => {
+    const cached = cache.get(title)
+    if (cached) {
+      return cached.value
+    }
+    const value = classify(title)
+    // Insertion-ordered FIFO eviction: a pane's superseded title frames are the
+    // oldest keys and the least likely to be asked for again.
+    if (cache.size >= MAX_MEMOIZED_TITLES) {
+      const oldest = cache.keys().next()
+      if (!oldest.done) {
+        cache.delete(oldest.value)
+      }
+    }
+    cache.set(title, { value })
+    return value
+  }
+}