Studio: lighten chat text weight on Linux to match macOS rendering (#7308)

* Studio: lighten chat text weight on Linux to match macOS rendering

* Exclude custom interface fonts from the Linux chat weight compensation

* Simplify Linux chat font weight override

studio/frontend/src/features/settings/stores/appearance-custom-store.ts

@@ -479,6 +479,8 @@ export function applyCustomizationToDocument(
     "--font-sans",
     c.uiFont ? `"${c.uiFont}", ${DEFAULT_SANS_STACK}` : null,
   );
+  // Custom interface fonts cascade into chat and opt out of its Inter tuning.
+  el.toggleAttribute("data-ui-font", Boolean(c.uiFont));
   setVar(
     "--font-heading",
     c.headingFont ? `"${c.headingFont}", ${DEFAULT_HEADING_STACK}` : null,

studio/frontend/src/index.css

@@ -633,6 +633,13 @@ html.no-font-smoothing body {
 	-moz-osx-font-smoothing: auto;
 }
 
+/* Match Inter's lighter macOS rendering. Keep 410 when smoothing is off or a
+   custom font reaches chat. */
+html.render-linux:not(.no-font-smoothing):not([data-chat-font]):not([data-ui-font])
+	:is(.aui-assistant-message-root, .aui-user-message-root) {
+	font-weight: 350;
+}
+
 /* Chat font: only applies while a custom chat font is set. Elements with
    explicit font utilities (headings, code) keep their own families. */
 html[data-chat-font] .aui-root {

studio/frontend/src/main.tsx

@@ -36,6 +36,13 @@ if (!rootElement) {
 
 initializeLocale();
 
+// Rasterization follows the browser OS, not the potentially remote server.
+// This adjustment is calibrated for desktop Linux, so exclude Android.
+const uaLower = navigator.userAgent.toLowerCase();
+if (uaLower.includes("linux") && !uaLower.includes("android")) {
+  document.documentElement.classList.add("render-linux");
+}
+
 createRoot(rootElement).render(
   <StrictMode>
     <App />