Display loss recovery attempt for track-wlroots 0.18 branch

Here is my attempt at display loss recovery implementation for wlroots 0.18:

https://gist.github.com/kode54/58b9e30ed73f82e1cfb040fe84f36c66

It doesn't work so well.

Last attempt crashes with this backtrace:

#0  __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, 
    no_tid=no_tid@entry=0) at pthread_kill.c:44
44	     return INTERNAL_SYSCALL_ERROR_P (ret) ? INTERNAL_SYSCALL_ERRNO (ret) : 0;

#0  __pthread_kill_implementation
    (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at pthread_kill.c:44
#1  0x0000790b680a5463 in __pthread_kill_internal (threadid=<optimized out>, signo=6)
    at pthread_kill.c:78
#2  0x0000790b6804c120 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#3  0x0000790b680334c3 in __GI_abort () at abort.c:79
#4  0x0000790b680333df in __assert_fail_base
    (fmt=0x790b681c3c20 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=assertion@entry=0x5aacbd5146cd "handle || is_shutting_down()", file=file@entry=0x5aacbd5143de "../src/core/output-layout.cpp", line=line@entry=1709, function=function@entry=0x5aacbd517ae0 "wf::output_t* wf::output_layout_t::impl::get_output_coords_at(const wf::pointf_t&, wf::pointf_t&)") at assert.c:94
#5  0x0000790b68044177 in __assert_fail
    (assertion=0x5aacbd5146cd "handle || is_shutting_down()", file=0x5aacbd5143de "../src/core/output-layout.cpp", line=1709, function=0x5aacbd517ae0 "wf::output_t* wf::output_layout_t::impl::get_output_coords_at(const wf::pointf_t&, wf::pointf_t&)") at assert.c:103
#6  0x00005aacbd45f7a8 in wf::output_layout_t::impl::get_output_coords_at(wf::pointf_t const&, wf::pointf_t&) [clone .part.0] [clone .lto_priv.0]
    (closest=<optimized out>, origin=<optimized out>, this=<optimized out>)
    at ../src/core/output-layout.cpp:1709
#7  0x00005aacbd4782c0 in wf::output_layout_t::impl::get_output_coords_at
    (origin=<synthetic pointer>..., this=0x5aace2698960, closest=...) at ../src/core/core.cpp:297
#8  wf::output_layout_t::get_output_coords_at (this=<optimized out>, origin=..., closest=...)
    at ../src/core/output-layout.cpp:1762
#9  wf::compositor_core_impl_t::reconfigure_outputs (this=0x5aace0cd5430)
    at ../src/core/core.cpp:239
#10 0x00005aacbd513796 in main::{lambda(void*)#1}::operator()(void*) const [clone .isra.0]
    (__closure=0x5aace18aca20, data=<optimized out>) at ../src/main.cpp:458
#11 0x00005aacbd442c82 in std::function<void(void*)>::operator()
    (this=<optimized out>, __args#0=<optimized out>)
    at /usr/include/c++/14.2.1/bits/std_function.h:591
#12 wf::wl_listener_wrapper::emit (this=<optimized out>, data=<optimized out>)
    at ../src/wl-listener-wrapper.tpp:57
#13 wf::handle_wrapped_listener (listener=<optimized out>, data=<optimized out>)
    at ../src/wl-listener-wrapper.tpp:10
#14 0x0000790b68a0342e in wl_signal_emit_mutable
    (signal=signal@entry=0x5aace0fc13b8, data=data@entry=0x0)
    at ../wayland-1.23.0/src/wayland-server.c:2314
#15 0x0000790b68913b5f in begin_gles2_buffer_pass
    (buffer=0x5aace1e82560, prev_ctx=0x7ffc170a37a0, timer=0x0)
    at ../wlroots-hidpi-xprop/render/gles2/pass.c:258
#16 gles2_begin_buffer_pass
    (wlr_renderer=<optimized out>, wlr_buffer=0x5aace1e4eb30, options=<optimized out>)
    at ../wlroots-hidpi-xprop/render/gles2/renderer.c:262
#17 0x0000790b6890ce35 in wlr_renderer_begin_buffer_pass
    (renderer=<optimized out>, buffer=<optimized out>, options=<optimized out>)
    at ../wlroots-hidpi-xprop/render/wlr_renderer.c:304
#18 0x00005aacbd4f71da in wf::swapchain_damage_manager_t::start_frame (this=0x5aace1745de0)
    at ../src/output/render-manager.cpp:331
#19 wf::render_manager::impl::paint (this=0x5aace1d6b1b0) at ../src/output/render-manager.cpp:1130
#20 0x00005aacbd442ce6 in std::function<void()>::operator() (this=<optimized out>)
    at /usr/include/c++/14.2.1/bits/std_function.h:591
#21 handle_timeout (data=<optimized out>) at ../src/util.cpp:31
#22 0x0000790b68a053a6 in wl_timer_heap_dispatch (timers=0x5aace0cd5388)
    at ../wayland-1.23.0/src/event-loop.c:527
#23 wl_event_loop_dispatch (loop=0x5aace0cd5330, timeout=<optimized out>, timeout@entry=-1)
    at ../wayland-1.23.0/src/event-loop.c:1098
#24 0x0000790b68a0710f in wl_display_run (display=0x5aace0cd5240)
    at ../wayland-1.23.0/src/wayland-server.c:1530
#25 0x00005aacbd4410bb in main (argc=<optimized out>, argv=<optimized out>) at ../src/main.cpp:509

And then it drops to a terminal and fails to restart cage as my login manager, and hangs the GPU completely.

Start with the linked gist and the assertion in src/core/output-layout.cpp:1709, then trace the callers through src/core/core.cpp and src/output/render-manager.cpp. Compare the display-loss path with the wlroots 0.18 branch and reproduce the failure described in the backtrace. Done means display loss is recovered without the assertion, terminal fallback, login-manager restart failure, or GPU hang.