Fix running server and GUI together on macOS

[azeey]

🦟 Bug fix

Summary

On macOS Metal API is requires initialization from the main thread. As a result, we currently cannot run worlds with rendering sensors on macOS without running the server and GUI seprately, i.e, gz sim camera_sensors.sdf crashes with the following stacktrace

#6    Object "libsystem_pthread.dylib", at 0x195c9bbc7, in _pthread_start + 135
#5    Object "libgz-sim-sensors-system.11.0.0~pre", at 0x120c3f56b, in void* std::__1::__thread_proxy[abi:ne190102]<std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct>>, void (gz::sim::v11::systems::SensorsPrivate::*)(), gz::sim::v11::systems::SensorsPrivate*>>(void*) + 71
#4    Object "libgz-sim-sensors-system.11.0.0~pre", at 0x120c28b9f, in gz::sim::v11::systems::SensorsPrivate::RenderThread() + 175
#3    Object "libgz-sim-sensors-system.11.0.0~pre", at 0x120c27a57, in gz::sim::v11::systems::SensorsPrivate::WaitForInit() + 691
#2    Object "libsystem_platform.dylib", at 0x195cd56a3, in _sigtramp + 55
#1    Object "gz-sim-main", at 0x104fd002f, in backward::SignalHandling::sig_handler(int, __siginfo*, void*) + 19
#0    Object "gz-sim-main", at 0x104fd0087, in backward::SignalHandling::handleSignal(int, __siginfo*, void*) + 59
[1]    21922 segmentation fault  gz sim -v4 camera_sensor.sdf

This PR fixes this be ensuring the server runs on the main thread (using the blocking=true flag on Server::Run) and creating a separate thread to monitor the GUI process.

joint_server_gui.mp4

Checklist

• Signed all commits for DCO
• Added a screen capture or video to the PR description that demonstrates the fix (as needed)
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• Updated Bazel files (if adding new files). Created an issue otherwise.
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Generated-By: Gemini 2.5 Pro

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[arjo129]

Nice! Tested it on my mac and it works. We seem to have broken Bazel for mac os in gz-common?

[iche033]

Nice! Tested it on my mac and it works. We seem to have broken Bazel for mac os in gz-common?

gazebosim/gz-common#795 should fix the bazel builds

[azeey]

@Mergifyio backport gz-sim10

[mergify]

backport gz-sim10

✅ Backports have been created

Details

• #3424 Fix running server and GUI together on macOS (backport #3405) has been created for branch gz-sim10