fix(webview): use GTK's software renderer when the helper composites in software

GTK's GL renderer aborted in libepoxy while snapshotting a page switch, which closed the web view. GSK_RENDERER set by the user still wins.

CHANGELOG.md

@@ -37,6 +37,9 @@ GitHub are taken from the matching section here.
   renderer.
 - Clicking while a Roblox text box has focus no longer closes it. Only Roblox
   decides when a click ends typing.
+- Going to another page in the web view, such as Friends from a profile, no
+  longer closes the web view. It crashed on every page change on Wayland
+  systems whose GL setup GTK could not use.
 
 ## [0.3.2] - 2026-09-29
 

src/webview/mocktail_webview_helper.cc

@@ -1424,6 +1424,11 @@ void Activate(GtkApplication* application, gpointer user_data) {
   state->disable_hardware_acceleration =
       mocktail::webview::ShouldDisableWebViewHardwareAcceleration(
           wayland_display, std::getenv("WEBKIT_DISABLE_COMPOSITING_MODE"));
+  // GTK picks its renderer when a window is realized, which is after this.
+  if (mocktail::webview::ShouldForceSoftwareGtkRenderer(
+          state->disable_hardware_acceleration, std::getenv("GSK_RENDERER"))) {
+    setenv("GSK_RENDERER", "cairo", 0);
+  }
   std::cerr << "[webview] display=" << (wayland_display ? "wayland" : "other")
             << " compositing="
             << (state->disable_hardware_acceleration ? "software" : "default")

src/webview/webview_helper_policy.cc

@@ -133,6 +133,11 @@ bool ShouldDisableWebViewHardwareAcceleration(
   return wayland_display;
 }
 
+bool ShouldForceSoftwareGtkRenderer(bool software_compositing,
+                                    const char* renderer_override) {
+  return software_compositing && renderer_override == nullptr;
+}
+
 const char* AndroidBridgeSource() { return kBridgeSource; }
 
 std::string BuildRobloxAndroidUserAgent() {

src/webview/webview_helper_policy.h

@@ -38,6 +38,13 @@ bool ShouldDisableWebKitSandbox(std::string_view kernel_version,
 // Match WebKit's WEBKIT_DISABLE_COMPOSITING_MODE override semantics.
 bool ShouldDisableWebViewHardwareAcceleration(
     bool wayland_display, const char* compositing_override);
+// GTK's GL renderer aborts in libepoxy when it snapshots a page switch on
+// hosts where its GL context cannot become current. With software compositing
+// the helper does not need GL for its UI, so use the Cairo renderer unless the
+// user chose one through GSK_RENDERER.
+bool ShouldForceSoftwareGtkRenderer(bool software_compositing,
+                                    const char* renderer_override);
+
 const char* AndroidBridgeSource();
 std::string BuildRobloxAndroidUserAgent();
 bool IsBrowserLoginUrl(std::string_view url);

tests/webview_helper_policy_test.cc

@@ -134,6 +134,19 @@ TEST(WebViewHelperPolicyTest, HonorsExplicitCompositingEnvironment) {
   }
 }
 
+TEST(WebViewHelperPolicyTest, ForcesCairoRendererWithSoftwareCompositing) {
+  EXPECT_TRUE(ShouldForceSoftwareGtkRenderer(true, nullptr));
+  EXPECT_FALSE(ShouldForceSoftwareGtkRenderer(false, nullptr));
+}
+
+TEST(WebViewHelperPolicyTest, HonorsExplicitGtkRendererEnvironment) {
+  for (bool software_compositing : {false, true}) {
+    for (const char* value : {"gl", "vulkan", "cairo", ""}) {
+      EXPECT_FALSE(ShouldForceSoftwareGtkRenderer(software_compositing, value));
+    }
+  }
+}
+
 TEST(WebViewHelperPolicyTest, AllowsOnlyTlsTopLevelNavigation) {
   const UriPolicyResult roblox =
       EvaluateNavigationUri("https://www.roblox.com/login");