fix: connect toolbar double clicks to native window zoom

Cargo.toml

@@ -21,8 +21,8 @@ winit = "0.30.13"
 
 [target.'cfg(target_os = "macos")'.dependencies]
 objc2 = "0.5.2"
-objc2-app-kit = { version = "0.2.2", default-features = false, features = ["NSButton", "NSView", "NSWindow"] }
-objc2-foundation = { version = "0.2.2", default-features = false, features = ["NSGeometry"] }
+objc2-app-kit = { version = "0.2.2", default-features = false, features = ["NSApplication", "NSButton", "NSEvent", "NSView", "NSWindow"] }
+objc2-foundation = { version = "0.2.2", default-features = false, features = ["NSGeometry", "NSString", "NSUserDefaults"] }
 
 [profile.release]
 lto = "thin"

docs/ui-workspace-audit.md

@@ -201,3 +201,32 @@ selection changes to the clicked tab and idle separators return after leaving.
 The capture API does not establish frame-accurate 160 ms timing. Offline
 all-target Clippy, formatting, release bundling and whitespace checks passed;
 no cargo test, automated smoke script or Docker task was run.
+
+
+### Native toolbar double-click — 2026-10-25
+
+The custom row previously called only winit's native window-drag operation;
+a manual double-click in its empty area did not resize the window. The same
+empty-area hit test now consults AppKit's current NSEvent clickCount before
+starting a drag. On the second press it calls NSWindow.performZoom, preserving
+AppKit's standard/user frame toggle and avoiding a hand-built resize animation.
+Tabs, close buttons and + remain excluded from this handler.
+
+The adapter reads AppleActionOnDoubleClick without changing system preferences:
+Minimize calls performMiniaturize; absent/Maximize calls performZoom; disabled
+or unknown values do nothing. Fill also uses the public performZoom action,
+whose standard frame fills this application's available screen in the checked
+configuration. It does not invoke the private _zoomFill selector used by Chrome.
+Consequently Fill is not claimed to reproduce every macOS tiling margin rule.
+Native fullscreen uses a different window state and is left to AppKit.
+
+References: Apple's [performZoom](https://developer.apple.com/documentation/appkit/nswindow/performzoom(_:))
+and Chromium's [custom draggable-area handling](https://github.com/chromium/chromium/blob/main/components/remote_cocoa/app_shim/native_widget_mac_nswindow.mm).
+
+Manual native verification: an empty-row double-click changed the Retina window
+from 2560×1600 to 3024×1888; a second double-click restored 2560×1600. Clicking
++ and double-clicking a tab did not zoom the window. Dragging empty toolbar
+space continued to move the window. The user's double-click preference was
+absent (default zoom); other preference branches were not changed or manually
+tested. Offline all-target Clippy, formatting, release bundling and whitespace
+checks passed. No cargo test or automated smoke script was run.

src/app.rs

@@ -1410,6 +1410,10 @@ impl ApplicationHandler<AppEvent> for TesseraApp {
                         && self.pointer.x >= crate::tabs::LEADING
                         && self.tab_hit().is_none()
                     {
+                        #[cfg(target_os = "macos")]
+                        if crate::native_chrome::titlebar_double_click(&window) {
+                            return;
+                        }
                         let _ = window.drag_window();
                     }
                     if self.pointer.y >= crate::tabs::height(&[]) {

src/native_chrome.rs

@@ -1,11 +1,52 @@
 //! Keep AppKit's real window buttons aligned with the custom tab strip.
-use objc2_app_kit::{NSView, NSWindowButton, NSWindowStyleMask};
-use objc2_foundation::NSPoint;
+use objc2_app_kit::{NSApplication, NSView, NSWindowButton, NSWindowStyleMask};
+use objc2_foundation::{MainThreadMarker, NSPoint, NSString, NSUserDefaults};
 use winit::{
     raw_window_handle::{HasWindowHandle, RawWindowHandle},
     window::Window,
 };
 
+/// The custom draggable row does not receive AppKit's titlebar double-click
+/// action automatically. Use the native click count and native window actions.
+pub fn titlebar_double_click(window: &Window) -> bool {
+    let Some(main_thread) = MainThreadMarker::new() else {
+        return false;
+    };
+    let Ok(handle) = window.window_handle() else {
+        return false;
+    };
+    let RawWindowHandle::AppKit(handle) = handle.as_raw() else {
+        return false;
+    };
+    // SAFETY: called on the event-loop thread during a left-button press, with
+    // a live winit-owned NSView. No native object outlives the Window borrow.
+    unsafe {
+        let Some(event) = NSApplication::sharedApplication(main_thread).currentEvent() else {
+            return false;
+        };
+        if event.clickCount() != 2 {
+            return false;
+        }
+        let view = &*handle.ns_view.as_ptr().cast::<NSView>();
+        let Some(native) = view.window() else {
+            return false;
+        };
+        if native.styleMask().contains(NSWindowStyleMask::FullScreen) {
+            return true;
+        }
+        let action = NSUserDefaults::standardUserDefaults()
+            .stringForKey(&NSString::from_str("AppleActionOnDoubleClick"))
+            .map(|value| value.to_string());
+        match action.as_deref() {
+            Some("Minimize") => native.performMiniaturize(None),
+            None | Some("Maximize" | "Fill") => native.performZoom(None),
+            // Respect disabled/unrecognized system actions without moving it.
+            _ => {}
+        }
+    }
+    true
+}
+
 /// Called only on winit's main thread, after native creation and before drawing.
 /// AppKit can restore its default button positions when laying out the title bar.
 pub fn align_controls(window: &Window) {