fix(kms): don't panic when renderer creation fails after a GPU reset

When the DRM device is lost transiently, for example when the amdgpu driver
performs a GPU reset and recovers ("device wedged, but recovered through
reset"), acquiring a renderer in `SurfaceThreadState::redraw` fails. The three
`renderer`/`single_renderer` calls used `.unwrap()`, so the failure panicked
the surface's render thread. Because that panic unwinds across the EGL/GBM FFI
boundary it aborts the whole process (SIGABRT), dropping the session back to
the greeter and closing every running application.

`redraw` is already fallible and its caller logs the error and reschedules a
redraw, and the frame-submission path (`render_frame`/`queue_frame`) already
propagates errors the same way. Propagate the renderer-acquisition errors too,
so a transient device loss is retried on the next frame, once the device is
back, instead of taking down the compositor.

Relates to #649.

Assisted by an AI coding tool; I have reviewed and fully understand the change
and am able to maintain it and respond to review.

src/backend/kms/surface/mod.rs

@@ -1006,12 +1006,16 @@ impl SurfaceThreadState {
             &self.shell.read(),
         );
 
+        // Acquiring a renderer can fail transiently when the underlying DRM
+        // device is lost (e.g. after a GPU reset).
         let mut renderer = if render_node != self.target_node {
             self.api
                 .renderer(&render_node, &self.target_node, compositor.format())
-                .unwrap()
+                .map_err(|err| anyhow::format_err!("Failed to create renderer: {:?}", err))?
         } else {
-            self.api.single_renderer(&self.target_node).unwrap()
+            self.api
+                .single_renderer(&self.target_node)
+                .map_err(|err| anyhow::format_err!("Failed to create renderer: {:?}", err))?
         };
 
         self.timings.start_render(&self.clock);
@@ -1267,7 +1271,10 @@ impl SurfaceThreadState {
                 })
                 .context("Failed to draw to offscreen render target")?;
 
-            renderer = self.api.single_renderer(&self.target_node).unwrap();
+            renderer = self
+                .api
+                .single_renderer(&self.target_node)
+                .map_err(|err| anyhow::format_err!("Failed to create renderer: {:?}", err))?;
 
             elements = postprocess_elements(
                 &mut renderer,