Old Electron version in macOS client causes GPU system lag and crashes in Tahoe (macOS 26)

**Describe the bug**
It appears that the Electron version packaged in the macOS desktop client triggers a widely reported issue with https://github.com/electron/electron/issues/48311. This results in system lag and WindowServer crashes that throw users out of their desktop session.

**To Reproduce**
shared/package.json suggests keybase should be using 38.2.2. Using ripgrep, the version in the current packaged macOS download from keybase.io (v6.5.4-20250917154415+52400b6f28) reports as 28.3.1, and includes the affected call:
```
f=/Applications/Keybase.app/Contents/Frameworks/Electron\ Framework.framework/Versions/A/Electron\ Framework
app=${f#/Applications/}; app=${app%%/Contents/*}

# Get Electron version
ev=$(rg -a -m1 -o -r '$1' 'Chrome/.*Electron/([0-9]+(\.[0-9]+){1,3})' -- "$f")
[ -z "$ev" ] && ev=$(rg -a -m1 -o -r '$1' 'Electron/([0-9]+(\.[0-9]+){1,3})' -- "$f")

# Ripgrep the binary for affected _cornerMask call (https://github.com/electron/electron/pull/48376)
if rg -a -q -F "_cornerMask" -- "$f"; then
echo -e "\033[31m❌ $app \033[2m(Electron ${ev:-})\033[0m"
else
echo -e "\033[32m✅ $app \033[2m(Electron ${ev:-})\033[0m"
fi
```
**Expected behavior**
The packaged Electron version should be one of:

* 36.9.2
* 37.6.0
* 38.2.0
* anything above 39

**Additional numbers**
The number 345567

Start with shared/package.json and compare its Electron version with the packaged macOS client reported in the issue. Check how the macOS download is built and verify the resulting Electron binary against the listed safe versions and the affected _cornerMask call. Done means a packaged client uses an unaffected Electron version.

Written by the indexing model from the issue text.