Electron, the web-wrapped app framework beloved by Microsoft’s Visual Studio Code, Slack, pgAdmin, Podman Desktop, Cursor, AWS Kiro, Theia IDE and the rest, ended up crippling system performance thanks to a grubby coding trick.

Last week, Electron maintainers ripped out an override of a private Cocoa API method called _cornerMask. The patch author admitted the method calculates window shadows and the override “forces WindowServer to repeatedly recalculate and repaint the shadow.” That party trick only broke Tahoe because Job’s Mob added new optimisations that promptly fell flat on their faces.

For the record, Apple’s rules state that methods starting with underscores are private and not meant to be touched. That didn’t stop Electron’s coders poking them anyway. The fallout is lousy performance whenever you’ve got more than one Electron app running.

Chrome and anything Chromium-based slowed to a crawl thanks to AutoFill bugs tied to Apple’s NSAutoFillHeuristicController. Rust’s Zed editor was another casualty. Job’s Mob grudgingly pushed out macOS 26.01 to “improve” AutoFill, though Chromium users reported that it is flaky.

The mess is tricky to untangle. Some blame Electron’s “dirty hack” while others insist Job’s Mob has “terrible QA.”

One developer who fixed the mess admitted: “Electron's _cornerMask override was a dirty hack that was made in an effort to fix an ancient issue with corner smoothing.” Another snapped that Apple “stopping developers from addressing shadowing issues in a custom manner with this kind of performance penalty is irresponsible at best … to me this falls into the ‘terrible QA’ category.”

The problem is not easily solved, since although the Electron team backported fixes as far back as version 36, developers must rebuild and ship their apps with the new code. Until then, users are stuck with laggy Macs or forced into workarounds like killing AutoFill entirely.

The safer option might be to hold off on installing Tahoe for a few months, giving Job’s Mob time to patch its mess and developers a chance to catch up. A more sensible suggestion is to buy a cheaper Windows based PC which does not have the problem.