Performance degradation over time + accelerated repro

[bearcage]

Issue Description

tl;dr unfocus/focus ghostty in a loop, watch send-rights climb on one port in lsmp

I noticed a significant gradual performance decline on an M3 max macbook with ghostty, safari, discord, and activity monitor and nothing else open. This first happened after not exiting ghostty for quite some time while doing ordinary work, so I started fishing for reasons why it might be slowing down.

I also had a decent chunk of cpu time on the system spent in WindowServer (in compositing tasks, per sample output), which cleared up on a reboot, so initialy I figured maybe unrelated, maybe red herring, maybe I just got unlucky, but it turns out actually this might be related.

Trying to see if I could reproduce the ghostty slowdown, I tried to think of things that I do in regular use which might provoke state changes — connecting and disconnecting external displays, sleeping and waking, alt-tabbing, copying/pasting, etc. I figured some of those I can artificially speed up, so I started with the easiest of those, alt-tabbing, and hit on something that looks legit. If you use applescript to slam unfocus/focus in a hot loop, you can pretty quickly reproduce the state I got in to.

The only thing I was able to dig up poking at the process which pointed to resource exhaustion or leaking (I'm not exactly a macOS expert, linux is my day job) was what looks like an ever-growing number of send-rights on one mach port in lsmp for ghostty.

Expected Behavior

Ideally not slow down

Actual Behavior

The whole system gets slow after a while of this abuse, in a way that doesn't seem to happen when doing the same to Safari or Apple's Terminal.app

Reproduction Steps

1. Open Ghostty
2. Open another terminal emulator and use it to run osascript -e 'repeat 4000 times' -e 'tell application "Finder" to activate' -e 'tell application "Ghostty" to activate' -e 'end repeat'
3. Do that a few more times (or pick a bigger repeat number)

As you go along, watch WindowServer's CPU load, and notice the frequency of flicker in window decoration focus display getting more uneven over time. Also note the system getting a little less predictably-instant doing things like switching focus to other applications (in between runs above, of course).

After a couple rounds of this, I'm able to get WindowServer's cpu load up to the mid-60% (with nothing going in ghostty, just a shell waiting for input). When you quit ghostty, WindowServer's cpu load will drop, but not to a normal idle-system level (mine in my latest run of these steps went from 68% to ~25%, and back up to 30% when I reopened ghostty to idle it).

Ghostty Logs

Timestamp                       Thread     Type        Activity             PID    TTL  
2026-03-24 01:29:45.853087-0700 0x194c     Debug       0x0                  664    0    ghostty: [com.mitchellh.ghostty:SecureInput] secure input state=true
2026-03-24 01:29:48.868001-0700 0x194c     Debug       0x0                  664    0    ghostty: [com.mitchellh.ghostty:SecureInput] secure input state=false
2026-03-24 01:29:48.972259-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local
2026-03-24 01:29:54.789598-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local
2026-03-24 01:30:50.527398-0700 0x4527b    Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:ghostty] Error while requesting notification authorization: Error Domain=UNErrorDomain Code=1 UserInfo={NSLocalizedDescription=<private>}
2026-03-24 01:32:39.764589-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local
2026-03-24 01:32:41.986640-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local
2026-03-24 01:32:52.538367-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local
2026-03-24 01:33:05.598772-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local
2026-03-24 01:33:10.156175-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local
2026-03-24 01:33:10.950137-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local
2026-03-24 01:33:15.801723-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local
2026-03-24 01:33:42.993950-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local
2026-03-24 01:33:43.374403-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local
2026-03-24 01:33:43.609587-0700 0x1e40     Error       0x0                  664    0    ghostty: [com.mitchellh.ghostty:io_handler] io_handler: OSC 7 host (zeal.local) must be local

Ghostty Version

Ghostty 1.3.1

Version
  - version: 1.3.1
  - channel: stable
Build Config
  - Zig version   : 0.15.2
  - build mode    : .ReleaseFast
  - app runtime   : .none
  - font engine   : .coretext
  - renderer      : renderer.generic.Renderer(renderer.Metal)
  - libxev        : kqueue

OS Version Information

macOS Tahoe 26.3.1 (a)

(Linux only) Display Server

None

(Linux only) Desktop Environment/Window Manager

No response

Minimal Ghostty Configuration

N/A — I only have a theme and shell-integration-features=ssh-env, neither of which should be related.a

Additional Relevant Configuration

No response

I acknowledge that:

• I have reviewed the FAQ and confirm that my issue is NOT among them.
• I have searched the Ghostty repository (both open and closed Discussions and Issues) and confirm this is not a duplicate of an existing issue or discussion.
• I have checked the "Preview" tab on all text fields to ensure that everything looks right, and have wrapped all configuration and code in code blocks with a group of three backticks (```) on separate lines.

EDIT: deleted redundancy — turns out typing on a machine that's slowed to a crawl is a bit of a struggle.