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/androidMain/kotlin/iris/platform/AndroidSecureStore.kt

@@ -134,6 +134,10 @@ class AndroidSecureStore(context: Context) : SecureStore {
         get() = prefs.getString(KEY_BACKGROUND_IMAGE_PATH, "").orEmpty()
         set(value) = prefs.edit().putString(KEY_BACKGROUND_IMAGE_PATH, value).apply()
 
+    override var fontSizeScale: Float
+        get() = prefs.getFloat(KEY_FONT_SIZE_SCALE, 1.0f)
+        set(value) = prefs.edit().putFloat(KEY_FONT_SIZE_SCALE, value).apply()
+
     override fun savePairing(url: String, token: String) {
         serverUrl = url
         this.token = token
@@ -162,5 +166,6 @@ class AndroidSecureStore(context: Context) : SecureStore {
         const val KEY_BACKGROUND_MODE = "background_mode"
         const val KEY_BACKGROUND_COLOR = "background_color"
         const val KEY_BACKGROUND_IMAGE_PATH = "background_image_path"
+        const val KEY_FONT_SIZE_SCALE = "font_size_scale"
     }
 }

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.

app/shared/src/commonMain/kotlin/iris/data/SecureStore.kt

@@ -57,6 +57,10 @@ interface SecureStore {
     /** UI setting: background image path (empty when unused). */
     var backgroundImagePath: String
 
+    /** UI setting: text size multiplier (1.0 = default; applied on top of the
+     *  system font scale). */
+    var fontSizeScale: Float
+
     fun savePairing(url: String, token: String)
     fun clear()
 }

app/shared/src/commonMain/kotlin/iris/state/IrisController.kt

@@ -204,6 +204,24 @@ class IrisController(
         store.backgroundImagePath = t.backgroundImagePath.orEmpty()
     }
 
+    // ── Font size (Settings → Appearance) ─────────────────────────────────
+    // Text-size multiplier applied app-wide via LocalDensity.fontScale (scales
+    // all sp text, not dp layout). Persisted; 1.0 = default.
+    private val _fontSizeScale = MutableStateFlow(store.fontSizeScale.coerceIn(FONT_SCALE_MIN, FONT_SCALE_MAX))
+    val fontSizeScale: StateFlow<Float> = _fontSizeScale.asStateFlow()
+
+    fun setFontSizeScale(scale: Float) {
+        val clamped = scale.coerceIn(FONT_SCALE_MIN, FONT_SCALE_MAX)
+        if (clamped == _fontSizeScale.value) return
+        _fontSizeScale.value = clamped
+        store.fontSizeScale = clamped
+    }
+
+    companion object {
+        const val FONT_SCALE_MIN = 0.8f
+        const val FONT_SCALE_MAX = 1.5f
+    }
+
     // ── M3: search state ──────────────────────────────────────────────────
     private val _searchResults = MutableStateFlow<List<SearchHit>>(emptyList())
     val searchResults: StateFlow<List<SearchHit>> = _searchResults.asStateFlow()

app/shared/src/commonMain/kotlin/iris/ui/screens/SettingsScreen.kt

@@ -65,6 +65,7 @@ fun SettingsScreen(controller: IrisController, onBack: () -> Unit) {
     val streamingEnabled by controller.streamingEnabled.collectAsState()
     val reasoningAutoCollapse by controller.reasoningAutoCollapse.collectAsState()
     val toolDetail by controller.toolDetail.collectAsState()
+    val fontSizeScale by controller.fontSizeScale.collectAsState()
     val theme = LocalUserTheme.current
     var pickerTarget by remember { mutableStateOf<PickerTarget?>(null) }
 
@@ -241,6 +242,46 @@ fun SettingsScreen(controller: IrisController, onBack: () -> Unit) {
                     }
                 }
             }
+            SettingsCard {
+                Text("🔤 Font size", fontSize = 14.sp)
+                Text(
+                    "Scale the text across the app",
+                    fontSize = 12.sp,
+                    color = IrisColors.textDim,
+                )
+                Spacer(modifier = Modifier.height(8.dp))
+                Row(verticalAlignment = Alignment.CenterVertically) {
+                    Text("Aa", fontSize = 12.sp, color = IrisColors.textDim)
+                    Slider(
+                        value = fontSizeScale,
+                        onValueChange = { controller.setFontSizeScale(it) },
+                        valueRange = IrisController.FONT_SCALE_MIN..IrisController.FONT_SCALE_MAX,
+                        modifier = Modifier.weight(1f),
+                    )
+                    Text("Aa", fontSize = 18.sp, color = IrisColors.textDim)
+                }
+                Row(
+                    verticalAlignment = Alignment.CenterVertically,
+                    modifier = Modifier.fillMaxWidth(),
+                ) {
+                    Text(
+                        "The quick brown fox jumps over the lazy dog",
+                        fontSize = 13.sp,
+                        color = IrisColors.textSecondary,
+                        modifier = Modifier.weight(1f),
+                    )
+                    Text(
+                        "${(fontSizeScale * 100).roundToInt()}%",
+                        fontSize = 12.sp,
+                        color = IrisColors.textDim,
+                    )
+                    if (fontSizeScale != 1.0f) {
+                        TextButton(onClick = { controller.setFontSizeScale(1.0f) }) {
+                            Text("Reset", fontSize = 12.sp)
+                        }
+                    }
+                }
+            }
             SettingsCard {
                 Row(
                     verticalAlignment = Alignment.CenterVertically,

app/shared/src/desktopMain/kotlin/iris/platform/DesktopSecureStore.kt

@@ -44,6 +44,7 @@ class DesktopSecureStore : SecureStore {
         val backgroundMode: String = "color",
         val backgroundColor: Int = UserTheme.DEFAULT_BACKGROUND,
         val backgroundImagePath: String = "",
+        val fontSizeScale: Float = 1.0f,
     )
 
     init {
@@ -206,6 +207,13 @@ class DesktopSecureStore : SecureStore {
             save(d.copy(backgroundImagePath = value))
         }
 
+    override var fontSizeScale: Float
+        get() = load().fontSizeScale
+        set(value) {
+            val d = load()
+            save(d.copy(fontSizeScale = value))
+        }
+
     override fun savePairing(url: String, token: String) {
         val d = load()
         save(d.copy(serverUrl = url.trim()))