Deregister Arabic shaping joiner when disposing pane

Since xterm.js does not automatically remove registered character joiners
upon terminal disposal, they must be explicitly deregistered to avoid
memory and registration leaks.

- Update `registerArabicShapingJoiner` to return a cleanup function.
- Store and call the cleanup handler when disposing a managed pane.
- Update tests to assert proper registration and deregistration.

src/renderer/src/lib/pane-manager/pane-dom-creation.ts

@@ -148,6 +148,7 @@ export function createPaneDOM(
     compositionHandler: null,
     focusClassSyncCleanup: null,
     terminalScrollIntentDisposable: null,
+    arabicShapingJoinerCleanup: null,
     pendingSplitScrollState: null,
     pendingSplitScrollRafIds: [],
     pendingSplitScrollTimerId: null,

src/renderer/src/lib/pane-manager/pane-lifecycle.ts

@@ -76,7 +76,7 @@ export function openTerminal(pane: ManagedPaneInternal): void {
   // Why: without run-joining, Arabic/Hebrew output renders as disconnected
   // letters in reversed order (#5262). Registered up front so restored
   // scrollback and reattach replays shape correctly, not just live output.
-  registerArabicShapingJoiner(terminal)
+  pane.arabicShapingJoinerCleanup = registerArabicShapingJoiner(terminal)
 
   // Why: the OS reads the focused textarea's screen rect at compositionstart to
   // decide where to display the IME candidate window. xterm positions that
@@ -230,6 +230,13 @@ export function disposePane(
   pane.focusClassSyncCleanup = null
   pane.terminalScrollIntentDisposable?.dispose()
   pane.terminalScrollIntentDisposable = null
+  // Deregister the RTL shaping joiner: terminal.dispose() below does not.
+  try {
+    pane.arabicShapingJoinerCleanup?.()
+  } catch {
+    /* ignore */
+  }
+  pane.arabicShapingJoinerCleanup = null
   if (pane.compositionHandler) {
     pane.terminal.element?.removeEventListener('compositionstart', pane.compositionHandler)
     pane.terminal.element?.removeEventListener('compositionupdate', pane.compositionHandler)

src/renderer/src/lib/pane-manager/pane-manager-types.ts

@@ -161,6 +161,9 @@ export type ManagedPaneInternal = {
   focusClassSyncCleanup?: (() => void) | null
   // Stored so disposePane() can remove user-scroll intent listeners.
   terminalScrollIntentDisposable?: IDisposable | null
+  // Stored so disposePane() can deregister the joiner; terminal.dispose()
+  // does not remove registered character joiners.
+  arabicShapingJoinerCleanup?: (() => void) | null
   // Why: splitPane reparents DOM; its delayed restore owns scroll until the
   // browser settles, so intermediate fits must not compete with it.
   pendingSplitScrollState: ScrollState | null

src/renderer/src/lib/pane-manager/terminal-arabic-shaping-joiner.test.ts

@@ -122,15 +122,24 @@ describe('findRtlJoinRanges', () => {
 })
 
 describe('registerArabicShapingJoiner', () => {
-  it('registers the range finder with the terminal and returns the joiner id', () => {
+  it('registers the range finder and returns a cleanup that deregisters it', () => {
     let registered: ((text: string) => [number, number][]) | null = null
+    let deregistered: number | null = null
     const terminal = {
       registerCharacterJoiner(handler: (text: string) => [number, number][]): number {
         registered = handler
         return 7
+      },
+      deregisterCharacterJoiner(joinerId: number): void {
+        deregistered = joinerId
       }
     }
-    expect(registerArabicShapingJoiner(terminal)).toBe(7)
+    const cleanup = registerArabicShapingJoiner(terminal)
     expect(registered).toBe(findRtlJoinRanges)
+    expect(deregistered).toBeNull()
+
+    // terminal.dispose() does not deregister joiners, so cleanup must.
+    cleanup()
+    expect(deregistered).toBe(7)
   })
 })

src/renderer/src/lib/pane-manager/terminal-arabic-shaping-joiner.ts

@@ -116,10 +116,15 @@ export function findRtlJoinRanges(text: string): [number, number][] {
   return ranges
 }
 
-/** Register the RTL shaping joiner on a terminal. Registration is per
- *  terminal instance and is torn down with the terminal itself. */
+/** Register the RTL shaping joiner on a terminal. Returns a cleanup that
+ *  deregisters the joiner — `Terminal.dispose()` does not remove registered
+ *  character joiners, so disposePane() must call this to avoid leaking the
+ *  registration (xtermjs/xterm.js#3289). */
 export function registerArabicShapingJoiner(
-  terminal: Pick<Terminal, 'registerCharacterJoiner'>
-): number {
-  return terminal.registerCharacterJoiner(findRtlJoinRanges)
+  terminal: Pick<Terminal, 'registerCharacterJoiner' | 'deregisterCharacterJoiner'>
+): () => void {
+  const joinerId = terminal.registerCharacterJoiner(findRtlJoinRanges)
+  return () => {
+    terminal.deregisterCharacterJoiner(joinerId)
+  }
 }