fix: prevent stale terminal buffer flash on worktree switch (#654)

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

@@ -36,9 +36,9 @@ export function useTerminalPaneGlobalEffects({
   // function can cancel it if the pane deactivates mid-flush.
   const pendingFlushRef = useRef<ReturnType<typeof setTimeout> | null>(null)
 
-  // Why: the deferred rAF (guardedResumeAndFit) must be cancellable when
-  // the pane deactivates before the rAF fires — otherwise it would call
-  // resumeRendering() on an already-suspended manager.
+  // Why: the deferred rAF (guardedFit) must be cancellable when the pane
+  // deactivates before the rAF fires — otherwise it would call
+  // fitAndFocusPanes() on a suspended manager.
   const pendingRafRef = useRef<number | null>(null)
 
   // Why: two independent code paths schedule fitPanes() after a worktree
@@ -58,12 +58,13 @@ export function useTerminalPaneGlobalEffects({
       return
     }
     if (isActive) {
-      // Why: resumeRendering() creates WebGL contexts for each pane, which
-      // blocks the renderer for 100–500 ms per pane on Windows (ANGLE →
-      // D3D11).  Deferring it into the rAF that runs after the pending-write
-      // drain lets the browser paint one frame with the DOM renderer so the
-      // terminal content appears immediately.  WebGL takes over seamlessly
-      // in the next frame without a visible flash.
+      // Why: resume WebGL immediately so the terminal shows its last-known
+      // state on the first painted frame.  On macOS, WebGL context creation
+      // is ~5 ms — fast enough to feel instant.  On Windows (ANGLE → D3D11)
+      // it can take 100–500 ms, but the alternative (deferring to a rAF
+      // after the pending-write drain) leaves the terminal blank for multiple
+      // frames, which is a worse UX tradeoff.
+      manager.resumeRendering()
 
       fitEpochRef.current++
       const epoch = fitEpochRef.current
@@ -89,16 +90,12 @@ export function useTerminalPaneGlobalEffects({
         pendingWritesRef.current.set(paneId, '')
       }
 
-      const guardedResumeAndFit = (): void => {
+      const guardedFit = (): void => {
         pendingRafRef.current = null
-        // Why: read managerRef.current at rAF time instead of capturing
-        // it at effect entry — the PaneManager instance can change if the
-        // component unmounts and remounts during rapid tab switches.
         const mgr = managerRef.current
         if (!mgr) {
           return
         }
-        mgr.resumeRendering()
         // Why: three-layer guard prevents redundant and stale fits.
         // 1. Staleness — reject callbacks from a superseded activation
         //    (e.g. rapid A→B→C worktree switch).
@@ -117,7 +114,7 @@ export function useTerminalPaneGlobalEffects({
       }
 
       if (entries.length === 0) {
-        pendingRafRef.current = requestAnimationFrame(guardedResumeAndFit)
+        pendingRafRef.current = requestAnimationFrame(guardedFit)
       } else {
         let entryIdx = 0
         let offset = 0
@@ -125,7 +122,7 @@ export function useTerminalPaneGlobalEffects({
         const drainNextChunk = (): void => {
           if (entryIdx >= entries.length) {
             pendingFlushRef.current = null
-            pendingRafRef.current = requestAnimationFrame(guardedResumeAndFit)
+            pendingRafRef.current = requestAnimationFrame(guardedFit)
             return
           }
 
@@ -159,8 +156,8 @@ export function useTerminalPaneGlobalEffects({
         clearTimeout(pendingFlushRef.current)
         pendingFlushRef.current = null
       }
-      // Cancel any pending rAF so guardedResumeAndFit doesn't call
-      // resumeRendering() on an already-suspended manager.
+      // Cancel any pending rAF so guardedFit doesn't run on a
+      // suspended manager.
       if (pendingRafRef.current !== null) {
         cancelAnimationFrame(pendingRafRef.current)
         pendingRafRef.current = null