fix: tighten mobile keyboard layout — eliminate dead space and toolbar overlap

- Remove redundant 50px CSS padding on terminal-container when keyboard visible
- Reduce JS paddingBottom constant from +94 to +84 (exact toolbar + accessory)
- Add _shrinkPaddingToFit() to eliminate terminal row quantization gap
- Add CSS padding-bottom on .main for fixed toolbar clearance (keyboard hidden)
- Match iOS Safari toolbar offset (100vh - --app-height) in .main padding

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/web/public/mobile-handlers.js

@@ -320,9 +320,10 @@ const KeyboardHandler = {
 
       // Shrink main content area so terminal doesn't extend behind keyboard.
       // Use stable keyboard height (not scroll-dependent) for padding.
+      // 84px = toolbar (40px) + accessory bar (44px).
       const keyboardHeight = this.initialViewportHeight - (window.visualViewport.height || window.innerHeight);
       if (main && keyboardHeight > 0) {
-        main.style.paddingBottom = `${keyboardHeight + 94}px`;
+        main.style.paddingBottom = `${keyboardHeight + 84}px`;
       }
     } else {
       this.resetLayout();
@@ -369,6 +370,11 @@ const KeyboardHandler = {
           try {
             app.fitAddon.fit();
           } catch {}
+        // Eliminate terminal row quantization gap: xterm can only show whole
+        // rows, so leftover pixels create dead space below the last row.
+        // Shrink .main's paddingBottom by the gap so the terminal fills flush
+        // to the accessory bar.
+        this._shrinkPaddingToFit();
         app.terminal.scrollToBottom();
         // Send resize to server so PTY dimensions match xterm
         this._sendTerminalResize();
@@ -424,6 +430,31 @@ const KeyboardHandler = {
     } catch {}
   },
 
+  /**
+   * Shrink .main paddingBottom to eliminate the terminal row quantization gap.
+   * xterm can only render whole rows, so fractional-row pixels create dead
+   * space below the last row. After fitAddon.fit(), measure the gap and
+   * reduce padding by that amount so the terminal sits flush against the bars.
+   */
+  _shrinkPaddingToFit() {
+    try {
+      const container = document.getElementById('terminalContainer');
+      const main = document.querySelector('.main');
+      if (!container || !main || typeof app === 'undefined' || !app.terminal) return;
+      const cellH = app.terminal._core?._renderService?.dimensions?.css?.cell?.height;
+      if (!cellH) return;
+      const gap = container.clientHeight - app.terminal.rows * cellH;
+      if (gap > 0 && gap < cellH) {
+        const currentPadding = parseInt(main.style.paddingBottom) || 0;
+        main.style.paddingBottom = currentPadding + gap + 'px';
+        if (app.fitAddon)
+          try {
+            app.fitAddon.fit();
+          } catch {}
+      }
+    } catch {}
+  },
+
   /** Check if element is an input that triggers keyboard (excludes terminal) */
   isInputElement(el) {
     if (!el) return false;

src/web/public/mobile.css

@@ -327,15 +327,27 @@ html.mobile-init .file-browser-panel {
     max-height: calc(36px + var(--safe-area-top));
   }
 
-  /* Add top margin to main content to account for fixed header */
+  /* Add top margin to main content to account for fixed header,
+     and bottom padding for the fixed toolbar (40px) so terminal
+     content doesn't extend behind it. JS overrides paddingBottom
+     when keyboard is visible, and resetLayout() clears the inline
+     style to re-expose this CSS value. */
   .main {
     margin-top: 42px;
+    padding-bottom: calc(40px + var(--safe-area-bottom));
   }
 
   .ios-device .main {
     margin-top: calc(42px + var(--safe-area-top));
   }
 
+  /* iOS Safari: toolbar is pushed up by (100vh - --app-height) to clear the
+     browser's bottom bar. Match that offset in main's padding so the terminal
+     doesn't extend behind the toolbar. */
+  .ios-device.safari-browser .main {
+    padding-bottom: calc(40px + var(--safe-area-bottom) + (100vh - var(--app-height, 100vh)));
+  }
+
   .header-right {
     padding-left: 0.2rem;
     gap: 0.1rem;
@@ -1586,11 +1598,9 @@ html.mobile-init .file-browser-panel {
     scroll-margin-top: 80px;
   }
 
-  /* When keyboard is visible, adjust content to account for moved toolbar */
-  .keyboard-visible .terminal-container {
-    /* Reduce terminal height when keyboard is up so it doesn't overlap toolbar */
-    padding-bottom: 50px;
-  }
+  /* When keyboard is visible, the JS paddingBottom on .main already reserves
+     space for toolbar + accessory bar. No extra padding needed here — it was
+     double-counting and creating dead space between terminal and the bars. */
 
   /* Ensure modals scroll properly when keyboard is visible */
   .keyboard-visible .modal-body {