GNOME Shell 49.8 segfaults at login when isolate-monitors=true on multi-monitor setup

[tmdag]

Describe the bug

On Fedora 43 / GNOME Shell 49.8, Dash to Panel v73 crashes GNOME Shell during login when isolate-monitors=true on a 3-monitor Wayland setup.

This is reproducible by changing only the Dash to Panel isolate-monitors setting.

System

• Fedora 43
• GNOME Shell 49.8
• Mutter 49.6
• GJS 1.86.0
• GLib 2.86.5
• GDM 49.2
• Dash to Panel v73
• Wayland session
• 3 monitors:
  • two Acer V277U external displays
  • one built-in LGD 2880x1920 display
• Mutter experimental features enabled:
  • scale-monitor-framebuffer
  • variable-refresh-rate

Reproduction

Working state:

• multi-monitors=true
• primary-monitor=''
• isolate-monitors=false
• enabled extensions: Apps Menu + Dash to Panel

Login succeeds and Dash to Panel is active.

Failing state:

• same setup, but set:
  • isolate-monitors=true

Then reboot/log out and log in through GDM.

Result

Password is accepted, GNOME session begins, then GNOME Shell segfaults before registering with GDM. GDM returns to the login screen and GNOME disables extensions after the crash.

Relevant log lines:

2026-07-05T10:25:24 gnome-shell[3947]: g_atomic_ref_count_dec: assertion 'old_value > 0' failed
2026-07-05T10:25:24 audit[3947]: ANOM_ABEND ... comm="gnome-shell" exe="/usr/bin/gnome-shell" sig=11
2026-07-05T10:25:24 kernel: gnome-shell[3947]: segfault ... in libglib-2.0.so.0.8600.5
2026-07-05T10:25:25 systemd-coredump: Process 3947 (gnome-shell) dumped core
2026-07-05T10:25:26 gdm: GdmDisplay: Session never registered, failing

coredumpctl info 3947 shows:

Signal: 11 (SEGV)
Package: gnome-shell/49.8-1.fc43
Top frame: g_variant_type_info_get_type_string (libglib-2.0.so.0)

## Expected result

GNOME Shell should not crash. Dash to Panel should either support isolate-monitors=true at login or fail gracefully without taking down the Shell.

## Workaround

Set:

gsettings --schemadir ~/.local/share/gnome-shell/extensions/dash-to-panel@jderose9.github.com/schemas \
  set org.gnome.shell.extensions.dash-to-panel isolate-monitors false

With isolate-monitors=false, login succeeds with Dash to Panel active.