From e15bb949d73e2c802d4db533039aaecef1409481 Mon Sep 17 00:00:00 2001
From: Neil <4138956+nwparker@users.noreply.github.com>
Date: Sat, 30 May 2026 14:11:19 -0700
Subject: [PATCH] perf: cache terminal tab lookup per tab array (#3938)

---
 .../components/terminal-pane/TerminalPane.tsx |  5 +-
 .../terminal-pane/terminal-tab-lookup.test.ts | 57 +++++++++++++++++++
 .../terminal-pane/terminal-tab-lookup.ts      | 25 ++++++++
 3 files changed, 85 insertions(+), 2 deletions(-)
 create mode 100644 src/renderer/src/components/terminal-pane/terminal-tab-lookup.test.ts
 create mode 100644 src/renderer/src/components/terminal-pane/terminal-tab-lookup.ts

diff --git a/src/renderer/src/components/terminal-pane/TerminalPane.tsx b/src/renderer/src/components/terminal-pane/TerminalPane.tsx
index 125bd8ee1f1..c08e9bec7a4 100644
--- a/src/renderer/src/components/terminal-pane/TerminalPane.tsx
+++ b/src/renderer/src/components/terminal-pane/TerminalPane.tsx
@@ -88,6 +88,7 @@ import {
   applyTerminalPaneAttentionToManager,
   subscribeTerminalPaneAttention
 } from './terminal-pane-attention-subscriptions'
+import { getCachedTerminalTabForWorktree } from './terminal-tab-lookup'
 
 type TerminalPaneProps = {
   tabId: string
@@ -335,8 +336,8 @@ export default function TerminalPane({
   )
   const clearCodexRestartNotice = useAppStore((store) => store.clearCodexRestartNotice)
   const savedLayout = useAppStore((store) => store.terminalLayoutsByTabId[tabId] ?? EMPTY_LAYOUT)
-  const terminalTab = useAppStore(
-    (store) => (store.tabsByWorktree[worktreeId] ?? []).find((tab) => tab.id === tabId) ?? null
+  const terminalTab = useAppStore((store) =>
+    getCachedTerminalTabForWorktree(store.tabsByWorktree, worktreeId, tabId)
   )
   const setTabLayout = useAppStore((store) => store.setTabLayout)
   const restoredLayout = useMemo(
diff --git a/src/renderer/src/components/terminal-pane/terminal-tab-lookup.test.ts b/src/renderer/src/components/terminal-pane/terminal-tab-lookup.test.ts
new file mode 100644
index 00000000000..a31fc9b0ec4
--- /dev/null
+++ b/src/renderer/src/components/terminal-pane/terminal-tab-lookup.test.ts
@@ -0,0 +1,57 @@
+import { describe, expect, it, vi } from 'vitest'
+import type { TerminalTab } from '../../../../shared/types'
+import { getCachedTerminalTabForWorktree } from './terminal-tab-lookup'
+
+function makeTab(id: string): TerminalTab {
+  return {
+    id,
+    ptyId: null,
+    worktreeId: 'wt-1',
+    title: id,
+    customTitle: null,
+    color: null,
+    sortOrder: 0,
+    createdAt: 0
+  }
+}
+
+function iterableTabs(tabs: TerminalTab[]): {
+  value: TerminalTab[]
+  iterator: ReturnType<typeof vi.fn>
+} {
+  const iterator = vi.fn(function* () {
+    yield* tabs
+  })
+  return {
+    value: { [Symbol.iterator]: iterator } as unknown as TerminalTab[],
+    iterator
+  }
+}
+
+describe('getCachedTerminalTabForWorktree', () => {
+  it('reuses the tab lookup while the worktree tab array is unchanged', () => {
+    const tabs = Array.from({ length: 200 }, (_, index) => makeTab(`tab-${index}`))
+    const { value, iterator } = iterableTabs(tabs)
+    const tabsByWorktree = { 'wt-1': value }
+
+    expect(getCachedTerminalTabForWorktree(tabsByWorktree, 'wt-1', 'tab-199')).toBe(tabs[199])
+    expect(getCachedTerminalTabForWorktree(tabsByWorktree, 'wt-1', 'tab-0')).toBe(tabs[0])
+
+    expect(iterator).toHaveBeenCalledTimes(1)
+  })
+
+  it('rebuilds the lookup when the tab array reference changes', () => {
+    const first = iterableTabs([makeTab('tab-1')])
+    const second = iterableTabs([makeTab('tab-2')])
+
+    expect(getCachedTerminalTabForWorktree({ 'wt-1': first.value }, 'wt-1', 'tab-1')?.id).toBe(
+      'tab-1'
+    )
+    expect(getCachedTerminalTabForWorktree({ 'wt-1': second.value }, 'wt-1', 'tab-2')?.id).toBe(
+      'tab-2'
+    )
+
+    expect(first.iterator).toHaveBeenCalledTimes(1)
+    expect(second.iterator).toHaveBeenCalledTimes(1)
+  })
+})
diff --git a/src/renderer/src/components/terminal-pane/terminal-tab-lookup.ts b/src/renderer/src/components/terminal-pane/terminal-tab-lookup.ts
new file mode 100644
index 00000000000..74447f0a87e
--- /dev/null
+++ b/src/renderer/src/components/terminal-pane/terminal-tab-lookup.ts
@@ -0,0 +1,25 @@
+import type { TerminalTab } from '../../../../shared/types'
+
+const terminalTabLookupByArray = new WeakMap<readonly TerminalTab[], Map<string, TerminalTab>>()
+
+export function getCachedTerminalTabForWorktree(
+  tabsByWorktree: Record<string, TerminalTab[]>,
+  worktreeId: string,
+  tabId: string
+): TerminalTab | null {
+  const tabs = tabsByWorktree[worktreeId]
+  if (!tabs) {
+    return null
+  }
+  let lookup = terminalTabLookupByArray.get(tabs)
+  if (!lookup) {
+    // Why: every mounted TerminalPane asks for its own tab on store updates.
+    // Build the per-array lookup once so 200 panes do not repeat the same scan.
+    lookup = new Map()
+    for (const tab of tabs) {
+      lookup.set(tab.id, tab)
+    }
+    terminalTabLookupByArray.set(tabs, lookup)
+  }
+  return lookup.get(tabId) ?? null
+}