Font size setting: app-wide text scale (0.8x-1.5x, default 1.0x) via Settings > Appearance slider — applied through LocalDensity.fontScale so all sp text scales while dp layout keeps its proportions; the multiplier stacks on top of the system font scale; persisted per platform (EncryptedSharedPreferences / settings.json) like the other appearance settings

app/shared/src/commonMain/kotlin/iris/IrisApp.kt

@@ -13,6 +13,8 @@ import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.layout.ContentScale
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.unit.Density
 import iris.data.SecureStore
 import iris.net.GatewayClient
 import iris.platform.setActiveController
@@ -55,9 +57,20 @@ fun IrisApp(
     }
     val state by controller.client.state.collectAsState()
     val theme by controller.theme.collectAsState()
+    val fontScale by controller.fontSizeScale.collectAsState()
+    val baseDensity = LocalDensity.current
 
     IrisTheme {
-        CompositionLocalProvider(LocalUserTheme provides theme) {
+        // Font-size setting (Settings → Appearance): a multiplier on top of the
+        // system font scale. fontScale affects sp text only — dp layout is
+        // untouched, so the UI keeps its proportions at any size.
+        CompositionLocalProvider(
+            LocalUserTheme provides theme,
+            LocalDensity provides Density(
+                density = baseDensity.density,
+                fontScale = baseDensity.fontScale * fontScale,
+            ),
+        ) {
             // The color goes through Surface's `color` parameter: a
             // Modifier.background on the Surface would be painted *under* the
             // Surface's own colorScheme.surface fill and never show through.