ClassicTitlebar

A small Ammonia tweak dylib that forces classic AppKit titlebars for whitelisted apps. Defaults ship with:

• Slack: /Slack.app/Contents/MacOS/Slack
• Apple Notes: /Notes.app/Contents/MacOS/Notes

Targeting uses Ammonia's native per-tweak whitelist. The companion file ClassicTitlebar.dylib.whitelist lists one substring per line; Ammonia injects the dylib when the line appears anywhere in the target process's executable path (from _NSGetExecutablePath, not the bundle identifier). Pick substrings narrow enough to avoid matching helpers and renderers — /Slack.app/Contents/MacOS/Slack matches Slack's main process but not Slack Helper. To target additional apps, add an exe-path substring to the installed whitelist and relaunch the app.

Build

make

This produces ClassicTitlebar.dylib. The linker auto-applies an adhoc,linker-signed signature, which is what macOS's page validator accepts at dlopen time. Do not re-sign with codesign --sign - — it rewrites the signature into a tool-signed form that gets rejected on load in some processes (e.g. Slack will SIGKILL with Invalid Page).

Install for Ammonia

make install

make install won't overwrite an existing whitelist; the default Slack+Notes whitelist is only installed if no whitelist file is present.

Or manually:

mkdir -p /private/var/ammonia/core/tweaks
cp ClassicTitlebar.dylib /private/var/ammonia/core/tweaks/
cp ClassicTitlebar.dylib.whitelist /private/var/ammonia/core/tweaks/

Then relaunch the whitelisted apps.

How it works

Each target window gets one of two treatments depending on its NSWindow subclass; classification happens at runtime, so adding a new app to the whitelist requires no code changes.

Base treatment — applied to every target window. Forces a standard titled NSWindow with FullSizeContentView stripped, ensures the titlebar is opaque and the title is visible, and unhides the traffic-light buttons. Toolbar / subtitle / titlebar-accessory APIs are left alone so native AppKit apps render their normal chrome.

Electron treatment — applied additionally when the window is an ElectronNSWindow. Electron treats its NSWindow as frameless and renders chrome in HTML; this branch undoes that:

1. Routes -[ElectronNSWindow contentRectForFrameRect:] through -originalContentRectForFrameRect: (Electron's preserved copy of the standard AppKit implementation). This is the load-bearing fix — AppKit and Chromium both then see a properly-inset content rect, so the contentView sits below the titlebar instead of extending behind it.
2. Strips any NSToolbar, subtitle, and titlebarAccessoryViewController set by Electron — they're vehicles for custom chrome, not real native UI.
3. Constrains NSTitlebarContainerView to 28pt and re-centers the traffic-light buttons. Slack re-inflates the container on web-content reloads via direct frame manipulation, so this is enforced inside a setFrame: swizzle on the container class. No periodic polling.

The two paths share the base treatment but the Electron branch only runs when CTIsElectronWindow() returns true.