bug(macOS): resize handle cursor (ew-resize/ns-resize) never appears — WKWebView pre-transform hit-test + tao cursor-rect override

[a5af]

Symptom

On macOS, CSS resize cursors (ew-resize, ns-resize) never appear when hovering over pane resize handles. The cursor stays as the default arrow. mouseenter/mouseleave events also fail to fire on the handles.

Root Cause — Two Stacked Bugs

Layer 1 — WKWebView hit-tests at pre-transform layout coordinates

WebKit's internal EventHandler::selectCursor() performs hit-testing using each element's layout bounding box, not its composited (visual) position. Our resize handles are positioned with transform: translateX/Y(N). The visual position differs from the layout position, so WebKit's cursor-selection hit-test finds the wrong element and the CSS cursor rule on the handle is never evaluated.

document.elementsFromPoint() uses composited coordinates and correctly finds the handle — but this is a different code path from WebKit's internal cursor selection.

Layer 2 — tao's NSView cursor-rect machinery overrides document.body.style.cursor

Even when we correctly detect the handle via elementsFromPoint and set document.body.style.cursor = 'ew-resize', this is overridden by macOS AppKit's resetCursorRects. Tauri's tao layer registers an addCursorRect covering the full NSView bounds, and the AppKit cursor-rect scan (which runs on every mouse-moved event) resets the cursor back to the tao-level default, overriding whatever WebKit set from web content.

A compounding factor: tauri#8770 confirmed that internal_on_mousemove was actively resetting the cursor to default on every mousemove on macOS (fixed in PR #8790). Verify the app runs a Tauri version that includes this fix.

What Was Tried

1. CSS cursor: ew-resize on the handle — fails due to Layer 1 (pre-transform hit-test)
2. elementsFromPoint on mousemove → document.body.style.cursor — correctly detects the handle (bypasses Layer 1) but fails due to Layer 2 (tao cursor-rect override resets it immediately)

Relevant Issues

Source	Issue	Status
wry	#175 — Cursor bug on macOS	Fixed (PR #220)
tauri	#8770 — internal_on_mousemove resets cursor on macOS	Fixed (PR #8790)
tauri	#2588 — macOS cursor weirdness	Closed as upstream WebKit
WebKit	Bug 101857 — cursor not updating on style change	Fixed (changeset 142861, 20 ms deferred update)
Safari 26.3	ticket 166731882 — ew-resize/ns-resize not displaying	Fixed in Safari 26.3 only
Apple Forums	WebView Doesn't Respect Cursor Properties	Workaround: override resetCursorRects

Candidate Fixes (ranked)

Fix 1 (Recommended): Window.setCursorIcon() via Tauri IPC

Replace document.body.style.cursor with getCurrentWindow().setCursorIcon('ewResize'). This calls tao's set_cursor_icon → AppKit NSCursor path at the window level, bypassing both WebKit's CSS cursor system (Layer 1) and the cursor-rect override (Layer 2). The elementsFromPoint detection is already in place — only the cursor-setting call changes.

import { getCurrentWindow } from '@tauri-apps/api/window';

let currentCursor = 'default';
const updateCursor = throttle(16, (x: number, y: number) => {
  if (isResizing()) return;
  const handle = document.elementsFromPoint(x, y).find(el => el.classList.contains('resize-handle'));
  const desired = handle
    ? (handle.classList.contains('flex-row') ? 'ewResize' : 'nsResize')
    : 'default';
  if (desired !== currentCursor) {
    currentCursor = desired;
    getCurrentWindow().setCursorIcon(desired);
  }
});

Requires "window:allow-set-cursor-icon" in the app's capabilities JSON.

Fix 2: Remove CSS transform from resize handles; use left/top positioning

Eliminates Layer 1 entirely. If the layout engine positions handles via left: Npx instead of transform: translateX(Npx), WebKit's hit-test finds the element at its visual position and CSS cursor rules work normally. May require layout engine changes.

Fix 3 (Quick attempt): will-change: transform on resize handles

Speculatively forces WebKit to promote the handle to a compositing layer. Some evidence suggests this may cause WebKit to use composited coordinates for hit-testing. 5-minute CSS-only change worth trying first.

.resize-handle { will-change: transform; }

Platform Notes

macOS	Safari	cursor ew-resize display	hit-test transform bug
Sequoia 15.x	18.x	Not present	Present
Tahoe 26.0–26.2	26.0–26.2	Present	Present
Tahoe 26.3+	26.3+	Fixed	Present

Fix must work on Safari 18.x (Sequoia) — still the majority of users (~52% macOS Tahoe adoption as of early 2026).

Full Analysis

Full investigation with deep-dive, source references, and additional candidate fixes: docs/investigations/wkwebview-cursor-transform-bug.md