diff --git a/src/main/ipc-channels.ts b/src/main/ipc-channels.ts
index ae1e9cc..6547fa1 100644
--- a/src/main/ipc-channels.ts
+++ b/src/main/ipc-channels.ts
@@ -33,6 +33,12 @@ export const IPC_MAINTENANCE_RESTART = 'maintenance:restart' as const;
 // powerSaveBlocker here instead. See got-feedback/feedback#686.
 export const IPC_POWER_SET_SCREEN_AWAKE = 'power:setScreenAwake' as const;
 
+// Main-window fullscreen-at-launch preference. Renderer (Settings → System)
+// reads/writes it; main persists it in the desktop config and applies it on
+// window creation.
+export const IPC_WINDOW_GET_START_FULLSCREEN = 'window:getStartFullscreen' as const;
+export const IPC_WINDOW_SET_START_FULLSCREEN = 'window:setStartFullscreen' as const;
+
 // Detachable panes (feedBack core's window.feedBack.panes).
 //
 // Deliberately tiny. The renderer OPENS its own pane windows with window.open() —
diff --git a/src/main/main.ts b/src/main/main.ts
index 7dd5adf..6c8a4cf 100644
--- a/src/main/main.ts
+++ b/src/main/main.ts
@@ -117,6 +117,8 @@ import {
     IPC_UPDATE_CHECK_NOW,
     IPC_UPDATE_APPLY,
     IPC_POWER_SET_SCREEN_AWAKE,
+    IPC_WINDOW_GET_START_FULLSCREEN,
+    IPC_WINDOW_SET_START_FULLSCREEN,
 } from './ipc-channels';
 import { initAudioBridge, shutdownAudio } from './audio-bridge';
 import { initDebugLogging, isDebugEnabled } from './debug-log';
@@ -469,6 +471,7 @@ function createWindow(port: number): void {
         getDesktopConfig().windowBounds,
         screen.getAllDisplays().map((d) => d.workArea),
     );
+    const startFullscreen = getDesktopConfig().startFullscreen === true;
     mainWindow = new BrowserWindow({
         x: restored.x,
         y: restored.y,
@@ -476,17 +479,20 @@ function createWindow(port: number): void {
         height: restored.height,
         minWidth: MIN_WIDTH,
         minHeight: MIN_HEIGHT,
+        fullscreen: startFullscreen,
         title: 'fee[dB]ack',
         backgroundColor: '#0f172a', // slate-900 to match Slopsmith UI
         webPreferences: rendererWebPreferences,
     });
-    if (restored.maximized) mainWindow.maximize();
+    if (restored.maximized && !startFullscreen) mainWindow.maximize();
 
     // Persist geometry on close. getNormalBounds() so a maximized session
     // saves the underlying windowed size, restored + re-maximized next launch.
-    // ponytail: fullscreen is deliberately not persisted (launching straight
-    // into fullscreen is jarring, especially on macOS) and we save on close
-    // only — a crash loses the last session's geometry; add debounced
+    // Fullscreen is NOT auto-persisted from the live window state (launching
+    // straight into fullscreen is jarring, especially on macOS); it launches
+    // fullscreen ONLY when the user opts in via Settings → System → "Start in
+    // fullscreen" (config.startFullscreen, applied above). We save geometry on
+    // close only — a crash loses the last session's geometry; add debounced
     // resize/move saving if that ever matters.
     mainWindow.on('close', () => {
         if (!mainWindow || mainWindow.isDestroyed()) return;
@@ -1272,6 +1278,23 @@ async function startup(): Promise<void> {
         return { success: true, enabled: on, urls: getLanUrls() };
     });
 
+    ipcMain.handle(IPC_WINDOW_GET_START_FULLSCREEN, () => getDesktopConfig().startFullscreen === true);
+    ipcMain.handle(IPC_WINDOW_SET_START_FULLSCREEN, (_event, on: unknown) => {
+        const value = on === true;
+        setDesktopConfig({ startFullscreen: value });
+        // Live-apply so the toggle is responsive, not silent-until-relaunch.
+        // Works on the first toggle on Windows/Linux. On macOS the FIRST enter on
+        // a window created windowed is dropped by AppKit (its native-fullscreen
+        // state machine isn't engaged until the window has been fullscreen once —
+        // creating with `fullscreen: true` engages it), so there it takes effect
+        // on next launch instead; the core Settings note tells macOS users that.
+        // Reliable live both ways once the window has entered fullscreen once.
+        if (mainWindow && !mainWindow.isDestroyed() && mainWindow.isFullScreen() !== value) {
+            mainWindow.setFullScreen(value);
+        }
+        return value;
+    });
+
     // Auto-update (Velopack). The renderer Settings panel reads the persisted
     // channel from localStorage and calls setChannel() on boot — we default
     // to 'stable' here so the first check runs against the safest feed even
diff --git a/src/main/preload.ts b/src/main/preload.ts
index 9ba1886..bac485e 100644
--- a/src/main/preload.ts
+++ b/src/main/preload.ts
@@ -30,6 +30,8 @@ import {
     IPC_UPDATE_EVENT_AVAILABLE,
     IPC_UPDATE_EVENT_DOWNLOADED,
     IPC_POWER_SET_SCREEN_AWAKE,
+    IPC_WINDOW_GET_START_FULLSCREEN,
+    IPC_WINDOW_SET_START_FULLSCREEN,
     IPC_MAINTENANCE_GET_PATHS,
     IPC_MAINTENANCE_RESET,
     IPC_MAINTENANCE_RESTART,
@@ -580,6 +582,14 @@ const feedBackDesktopApi = {
     power: {
         setScreenAwake: (keep: boolean) => ipcRenderer.invoke(IPC_POWER_SET_SCREEN_AWAKE, keep),
     },
+    // Main-window preferences the renderer can't own because the main process
+    // must read them at window-creation time. Today: start-in-fullscreen, wired
+    // by feedBack core's Settings → System "Start in fullscreen" toggle
+    // (setupWindowOptions()). Both methods return the resulting boolean.
+    window: {
+        getStartFullscreen: (): Promise<boolean> => ipcRenderer.invoke(IPC_WINDOW_GET_START_FULLSCREEN),
+        setStartFullscreen: (on: boolean): Promise<boolean> => ipcRenderer.invoke(IPC_WINDOW_SET_START_FULLSCREEN, on),
+    },
     // Detachable panes. The renderer opens its own pane windows with window.open()
     // — it moves a live DOM node into them and needs a handle on the new document
     // to do it — and Electron turns that into a real BrowserWindow, which main
diff --git a/src/main/soundfont-manager.ts b/src/main/soundfont-manager.ts
index c078738..345b67f 100644
--- a/src/main/soundfont-manager.ts
+++ b/src/main/soundfont-manager.ts
@@ -38,6 +38,13 @@ interface DesktopConfig {
     // Last main-window geometry, restored (after sanitization against the
     // current display layout) on next launch — see window-bounds.ts.
     windowBounds?: SavedWindowBounds;
+    // When true, the main window launches in fullscreen and the System-settings
+    // toggle that drives it is shown. Opt-in (default off) — this deliberately
+    // reverses createWindow()'s historical "never launch fullscreen" default,
+    // but only for users who ask for it. Persisted here (not renderer
+    // localStorage) because the main process must read it at window creation,
+    // before the renderer exists.
+    startFullscreen?: boolean;
     // Per-pane pop-out window geometry, keyed by pane id, plus its always-on-top
     // flag. Sanitized against the display layout on restore, exactly like
     // windowBounds — see pane-hosts.ts. Lives in the desktop config rather than