feat(app): navigate tabs on mousedown in new layout (#35042)

packages/app/src/components/titlebar-tab-nav.tsx

@@ -229,8 +229,17 @@ export function TabNavItem(props: {
             event.preventDefault()
             event.stopPropagation()
           }}
+          onMouseDown={(event) => {
+            // Navigate on mousedown to shave the press-release delay off tab switches.
+            if (event.button !== 0) return
+            if (editing()) return
+            if (props.suppressNavigation?.()) return
+            props.onNavigate()
+          }}
           onClick={(event) => {
             event.preventDefault()
+            // Mouse navigation already happened on mousedown; detail 0 means keyboard activation.
+            if (event.detail > 0) return
             if (editing()) return
             if (props.suppressNavigation?.()) return
             props.onNavigate()
@@ -368,8 +377,16 @@ export function DraftTabItem(props: {
           event.preventDefault()
           event.stopPropagation()
         }}
+        onMouseDown={(event) => {
+          // Navigate on mousedown to shave the press-release delay off tab switches.
+          if (event.button !== 0) return
+          if (props.suppressNavigation?.()) return
+          props.onNavigate()
+        }}
         onClick={(event) => {
           event.preventDefault()
+          // Mouse navigation already happened on mousedown; detail 0 means keyboard activation.
+          if (event.detail > 0) return
           if (props.suppressNavigation?.()) return
           props.onNavigate()
         }}