perf: skip hidden terminal sync fits

Skip sidebar sync-fit work for hidden display:none terminal panes while preserving visible and measurable startup panes.

src/renderer/src/components/terminal-pane/TerminalPane.tsx

@@ -1047,6 +1047,9 @@ export default function TerminalPane({
     cwd,
     isActive,
     isVisible,
+    // Why: hidden startup probes are opacity-hidden but measurable; ordinary
+    // hidden tabs are display:none and refit on visibility resume instead.
+    isSyncFitEnabled: isVisible || shouldMeasureHiddenStartup,
     paneCount,
     managerRef,
     containerRef,

src/renderer/src/components/terminal-pane/use-terminal-container-fit-sync.ts

@@ -5,12 +5,14 @@ import { fitPanes } from './pane-helpers'
 
 type UseTerminalContainerFitSyncArgs = {
   isVisible: boolean
+  isSyncFitEnabled: boolean
   managerRef: React.RefObject<PaneManager | null>
   containerRef: React.RefObject<HTMLDivElement | null>
 }
 
 export function useTerminalContainerFitSync({
   isVisible,
+  isSyncFitEnabled,
   managerRef,
   containerRef
 }: UseTerminalContainerFitSyncArgs): void {
@@ -21,10 +23,12 @@ export function useTerminalContainerFitSync({
   // ResizeObserver rAF would otherwise produce. The subsequent per-pane
   // ResizeObserver rAF and the 150ms debounced global fit become no-ops
   // because proposeDimensions() will match current cols/rows (early-return
-  // branch in safeFit). Listener is global (not gated on isVisible/isActive)
-  // so background tabs also fit, keeping their scroll position intact for
-  // when the user switches back.
+  // branch in safeFit). Hidden display:none panes cannot be measured
+  // accurately, so they skip this global path and refit on visibility resume.
   useEffect(() => {
+    if (!isSyncFitEnabled) {
+      return
+    }
     const onSyncFit = (): void => {
       managerRef.current?.fitAllPanes()
     }
@@ -32,7 +36,7 @@ export function useTerminalContainerFitSync({
     return () => {
       window.removeEventListener(SYNC_FIT_PANES_EVENT, onSyncFit)
     }
-  }, [managerRef])
+  }, [isSyncFitEnabled, managerRef])
 
   useEffect(() => {
     if (!isVisible) {

src/renderer/src/components/terminal-pane/use-terminal-pane-global-effects.test.ts

@@ -1,5 +1,7 @@
+/* eslint-disable max-lines -- Why: these hook tests share a mocked React lifecycle harness with global event cases. */
 import type * as ReactModule from 'react'
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { SYNC_FIT_PANES_EVENT } from '@/constants/terminal'
 import { useTerminalPaneGlobalEffects } from './use-terminal-pane-global-effects'
 
 const mocks = vi.hoisted(() => ({
@@ -82,6 +84,7 @@ function useMountForFileDrop(
     cwd?: string
     isActive?: boolean
     isVisible?: boolean
+    isSyncFitEnabled?: boolean
     paneCount?: number
   } = {}
 ): {
@@ -116,6 +119,7 @@ function useMountForFileDrop(
     cwd: options.cwd,
     isActive: options.isActive ?? true,
     isVisible: options.isVisible ?? true,
+    isSyncFitEnabled: options.isSyncFitEnabled ?? options.isVisible ?? true,
     paneCount: options.paneCount ?? 0,
     managerRef: { current: manager as never },
     containerRef: { current: null },
@@ -187,6 +191,7 @@ describe('useTerminalPaneGlobalEffects', () => {
       worktreeId: 'wt-1',
       isActive: true,
       isVisible: true,
+      isSyncFitEnabled: true,
       paneCount: 2,
       managerRef: { current: manager as never },
       containerRef: { current: null },
@@ -244,6 +249,7 @@ describe('useTerminalPaneGlobalEffects', () => {
       isActiveRef: { current: false },
       isVisibleRef: { current: false },
       paneCount: 1,
+      isSyncFitEnabled: true,
       toggleExpandPane: vi.fn()
     }
 
@@ -330,4 +336,74 @@ describe('useTerminalPaneGlobalEffects', () => {
 
     expect(mocks.handleTerminalFileDrop).not.toHaveBeenCalled()
   })
+
+  it('skips global sync-fit registration for hidden non-measurable terminal panes', () => {
+    const manager = {
+      getPanes: vi.fn(() => []),
+      resumeRendering: vi.fn(),
+      suspendRendering: vi.fn(),
+      fitAllPanes: vi.fn(),
+      getActivePane: vi.fn(() => null)
+    }
+
+    beginHookRender()
+    useTerminalPaneGlobalEffects({
+      tabId: 'tab-1',
+      worktreeId: 'wt-1',
+      isActive: false,
+      isVisible: false,
+      isSyncFitEnabled: false,
+      paneCount: 0,
+      managerRef: { current: manager as never },
+      containerRef: { current: null },
+      paneTransportsRef: { current: new Map() },
+      isActiveRef: { current: false },
+      isVisibleRef: { current: false },
+      toggleExpandPane: vi.fn()
+    })
+
+    const syncFitListener = vi
+      .mocked(window.addEventListener)
+      .mock.calls.find(([eventName]) => eventName === SYNC_FIT_PANES_EVENT)
+
+    expect(syncFitListener).toBeUndefined()
+  })
+
+  it('registers global sync-fit for measurable hidden startup panes', () => {
+    const manager = {
+      getPanes: vi.fn(() => []),
+      resumeRendering: vi.fn(),
+      suspendRendering: vi.fn(),
+      fitAllPanes: vi.fn(),
+      getActivePane: vi.fn(() => null)
+    }
+
+    beginHookRender()
+    useTerminalPaneGlobalEffects({
+      tabId: 'tab-1',
+      worktreeId: 'wt-1',
+      isActive: false,
+      isVisible: false,
+      isSyncFitEnabled: true,
+      paneCount: 0,
+      managerRef: { current: manager as never },
+      containerRef: { current: null },
+      paneTransportsRef: { current: new Map() },
+      isActiveRef: { current: false },
+      isVisibleRef: { current: false },
+      toggleExpandPane: vi.fn()
+    })
+
+    const syncFitListener = vi
+      .mocked(window.addEventListener)
+      .mock.calls.find(([eventName]) => eventName === SYNC_FIT_PANES_EVENT)
+
+    expect(syncFitListener).toBeDefined()
+    const listener = syncFitListener?.[1]
+    if (typeof listener !== 'function') {
+      throw new Error('expected sync-fit listener')
+    }
+    listener(new Event(SYNC_FIT_PANES_EVENT))
+    expect(manager.fitAllPanes).toHaveBeenCalledTimes(1)
+  })
 })

src/renderer/src/components/terminal-pane/use-terminal-pane-global-effects.ts

@@ -30,6 +30,7 @@ type UseTerminalPaneGlobalEffectsArgs = {
   cwd?: string
   isActive: boolean
   isVisible: boolean
+  isSyncFitEnabled: boolean
   paneCount: number
   managerRef: React.RefObject<PaneManager | null>
   containerRef: React.RefObject<HTMLDivElement | null>
@@ -45,6 +46,7 @@ export function useTerminalPaneGlobalEffects({
   cwd,
   isActive,
   isVisible,
+  isSyncFitEnabled,
   paneCount,
   managerRef,
   containerRef,
@@ -73,7 +75,7 @@ export function useTerminalPaneGlobalEffects({
     visibleResumeCompleteRef: wasVisibleRef,
     paneCount
   })
-  useTerminalContainerFitSync({ isVisible, managerRef, containerRef })
+  useTerminalContainerFitSync({ isVisible, isSyncFitEnabled, managerRef, containerRef })
 
   useEffect(() => {
     const manager = managerRef.current