[IDEA 2026.1] JCEF Chinese IME input not working on macOS even with OSR disabled

Problem description:

Environment:

IDE: IntelliJ IDEA [Ultimate/Community] [填写完整版本号，例如: 2026.1.0.251.xxxx]

OS: macOS [填写具体版本号，例如: 15.2 (24C101)]

JBR: [填写 JetBrains Runtime 版本，在 About 里能看到，例如: 21.0.6+13-b829.12]

Input Method: [填写输入法，例如: Native Pinyin / Sogou Pinyin]

Problem Description:
I am developing a plugin that embeds JBCefBrowser. On macOS, Chinese IME (Pinyin) input does not work at all — characters cannot be committed to the input field.

What I have already tried (Troubleshooting steps):

Disabled OSR via JBCefBrowser.createBuilder().setEnableOsr(false).

Disabled JCEF sandbox via Registry: ide.browser.jcef.sandbox.enable = false.

Set JVM flag -Dide.browser.jcef.osr.enabled=false in idea.vmoptions.

Verified that OSR is indeed false at runtime via System.getProperty.

Tested with both macOS native Pinyin and third-party Sogou Pinyin — neither works.

Actual Behavior:
Typing triggers no candidate window, and no characters are committed. The same plugin code works fine in a colleague's pre-release environment, but fails in the production environment with IDEA 2026.1.

Additional Detail:
The issue specifically occurs when typing into an <input> or <textarea> inside a cross-origin iframe embedded in the page. Input fields in the top-level page work normally / are also affected. (根据实际情况二选一)