feat: the + joins a lone file pane's top bar, beside Обновить and above the delete button, growing in smoothly

internal/server/web/static/app.css

@@ -340,6 +340,10 @@ body.multi .area { margin-top:0; border-top-left-radius:0; }
 body.split1 .float-add { top:42px; right:16px; }
 .float-add:hover, .float-add:focus-visible { opacity:1; background:var(--panel); }
 body.multi .float-add { opacity:0; pointer-events:none; }
+.float-add { transition:opacity .25s ease, background .25s ease, top .3s ease, right .3s ease, width .3s ease, height .3s ease, border-radius .3s ease; }
+/* In a file pane's top bar: a button like its neighbours. */
+.float-add.in-files { width:34px; height:34px; font-size:19px; opacity:1; border-radius:8px; }
+.float-add.in-files:hover { background:#151a21; }
 .tabview { position:absolute; inset:8px; opacity:0; visibility:hidden; transform:translateY(4px) scale(.995);
            transition:opacity .22s ease, transform .22s ease, visibility 0s .22s; }
 /* A tab fading out takes no pointer: a drop goes to the tab coming in. */

internal/server/web/static/workspace.js

@@ -101,6 +101,8 @@
     t.el.scrollIntoView({ block: 'nearest', inline: 'nearest', behavior: 'smooth' });
     if (desk && activePane) activePane.focus();
     updateMode();
+    // The tab comes in moving a little; the "+" goes by where it ends up.
+    setTimeout(placeFloat, 260);
   }
   function setActivePane(s) {
     activePane = s;
@@ -118,6 +120,20 @@
   // The corner "+" moves down out of the way of a split tab's title bars.
   function syncFloat() {
     document.body.classList.toggle('split1', tabs.length === 1 && tabs[0].panes.length > 1);
+    placeFloat();
+  }
+  // With one tab and a file pane in the top right corner, the "+" joins
+  // that pane's top bar: right of "Обновить", above "Удалить выбранное",
+  // a button of the same size. Otherwise it is back in the corner.
+  function placeFloat() {
+    const p = tabs.length === 1 ? tabs[0].panes.find(s => s.el.classList.contains('under-plus')) : null;
+    const bars = p && /files$/.test(p.kind) ? p.el.querySelectorAll('.fm-bar') : [];
+    const on = bars.length > 1 && bars[0].offsetParent !== null;
+    floatAdd.classList.toggle('in-files', on);
+    if (!on) { floatAdd.style.top = floatAdd.style.right = ''; return; }
+    const a = area.getBoundingClientRect(), top = bars[0].getBoundingClientRect(), row = bars[1].getBoundingClientRect();
+    floatAdd.style.top = (top.top - a.top - area.clientTop) + 'px';
+    floatAdd.style.right = (a.left + area.clientLeft + area.clientWidth - row.right) + 'px';
   }
   // One tab: a plain terminal, the strip folded into the corner "+".
   function updateMode() {
@@ -223,7 +239,7 @@
       g.style.left = d.x + 'px'; g.style.top = d.y + 'px'; g.style.width = d.w + 'px'; g.style.height = d.h + 'px';
     });
     clearTimeout(t.fitTimer);
-    t.fitTimer = setTimeout(() => t.panes.forEach(s => s.fit()), animate ? 270 : 0);
+    t.fitTimer = setTimeout(() => { t.panes.forEach(s => s.fit()); placeFloat(); }, animate ? 270 : 0);
   }
   function startResize(ev, t, g) {
     ev.preventDefault();