Harden Compose Desktop crash workarounds (macOS a11y + context-menu NPE)

[sproctor]

Two independent, unrecoverable upstream Compose Desktop crashes that reach production Sentry as fatal uncaught exceptions on the AWT event thread. Both are framework bugs with nothing for us to fix; the app should not die over them.

1. macOS a11y focus-target NPE (CMP-10170)

Reported on macOS (macbookair):

addFirst in unknown file
defaultAccessibilityFocusTarget in ComposeSceneAccessibility.kt [Line 169]
onAccessibleReceivedFocus in ComposeSceneAccessibility.kt [Line 86]
...
syncNodes in SemanticsOwnerAccessibility.kt

While retargeting a11y focus after a node is removed, defaultAccessibilityFocusTarget() walks the Accessible tree into an ArrayDeque, but getAccessibleChild() can return null and ArrayDeque rejects nulls (ComposeSceneAccessibility.kt:168-169). Still unguarded in compose-multiplatform 1.11.x.

We already swallow this in installUncaughtExceptionWorkaround, but the swallow is reactive: it only prevents process death. The crash happens mid syncNodes, so the a11y tree is left inconsistent and re-throws on the next focus change. It fires in practice only on macOS, whose a11y system aggressively queries AccessibleContext.

Fix: disable the Compose Desktop accessibility bridge on macOS by setting -Dcompose.accessibility.enable=false before the first window opens (Compose reads that system property lazily when it constructs the first ComposeSceneAccessibility). With the bridge off, accessibleContextProvider is null and the crashing focus-retarget path never runs.

• macOS only; Windows/Linux keep working screen-reader support and don't hit this in practice.
• An explicit -Dcompose.accessibility.enable=... on the command line is left untouched as an escape hatch.
• The existing uncaught-exception swallow stays as the cross-platform safety net.

Trade-off: no VoiceOver support on macOS until the upstream fix lands, which beats a crash loop.

2. Context-menu arrow-key NPE

Reported separately (not macOS-specific):

invoke-ZmokQxo in BasicContextMenuRepresentation.skiko.kt [Line 89]
invoke in BasicContextMenuRepresentation.skiko.kt [Line 80]
onKeyEvent-ZmokQxo in CanvasLayersComposeScene.skiko.kt [Line 586]
...
keyPressed in ComposeSceneMediator.desktop.kt

Pressing an arrow key while the text context menu (right-click Copy/Paste popup) is open runs DefaultOpenContextMenu's onKeyEvent handler, which calls FocusManager.moveFocus to step between menu items; that traversal NPEs inside Compose's focus machinery. The crashing frame is BasicContextMenuRepresentation_skikoKt$DefaultOpenContextMenu$2$1 (the Function1<KeyEvent, Boolean> key handler). Not accessibility-related; still unguarded in 1.11.x.

Fix: extend isKnownComposeBug to also swallow NullPointerExceptions whose stack contains a BasicContextMenuRepresentation frame, alongside the existing a11y focus-target guard. (Frame-name matching is reliable because the desktop build never runs ProGuard.)

Testing

• ./gradlew :desktopApp:ktlintCheck :desktopApp:compileKotlin pass.

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