feat: touch scroll for terminal and sidebar on mobile

Terminal: add touchstart/touchmove/touchend IIFE on #terminal-container.
Vertical swipe delta translated to _term.scrollLines(n). touchmove is
non-passive (required for e.preventDefault to block page scroll while
swiping inside terminal). mouse wheel scroll unaffected (separate wheel
event path in xterm.js).

Sidebar: add touch-action:pan-y + overscroll-behavior:contain to
.sidebar-list. Tells browser explicitly that vertical panning is allowed
and prevents scroll chaining when reaching list ends.

muxplex/frontend/style.css

@@ -427,6 +427,8 @@ body {
   display: flex;
   flex-direction: column;
   gap: 6px;
+  touch-action: pan-y;          /* tell browser vertical panning is allowed on mobile */
+  overscroll-behavior: contain; /* prevent scroll chaining to non-scrollable parent */
 }
 
 .sidebar-collapse-btn {

muxplex/frontend/terminal.js

@@ -246,3 +246,42 @@ function closeTerminal() {
 // ─── Expose to app.js ─────────────────────────────────────────────────────────
 window._openTerminal = openTerminal;
 window._closeTerminal = closeTerminal;
+
+// ---------------------------------------------------------------------------
+// Touch scroll — translates vertical swipe into xterm.js scrollback
+// ---------------------------------------------------------------------------
+// Runs once after DOM is ready. Mouse wheel scroll is unaffected (separate
+// `wheel` event path handled natively by xterm.js).
+;(function initTerminalTouchScroll() {
+  var container = document.getElementById('terminal-container');
+  if (!container || typeof container.addEventListener !== 'function') return;
+
+  var _touchLastY = 0;
+
+  container.addEventListener('touchstart', function (e) {
+    _touchLastY = e.touches[0].clientY;
+  }, { passive: true });
+
+  container.addEventListener('touchmove', function (e) {
+    if (!_term) return;
+    e.preventDefault(); // prevent page scroll while swiping inside terminal
+
+    var y = e.touches[0].clientY;
+    var deltaY = _touchLastY - y;   // positive = swipe up = scroll toward newer content
+    _touchLastY = y;
+
+    // Convert pixels to lines. xterm.js fontSize is set per device (12 mobile, 14 desktop).
+    // lineHeight ratio is 1.2 — gives ~14-17px per line.
+    var pxPerLine = (_term.options.fontSize || 14) * 1.2;
+    var lines = deltaY / pxPerLine;
+
+    // Only fire if movement is meaningful (avoids micro-jitter)
+    if (Math.abs(lines) >= 0.3) {
+      _term.scrollLines(Math.round(lines));
+    }
+  }, { passive: false }); // passive: false required to allow e.preventDefault()
+
+  container.addEventListener('touchend', function () {
+    _touchLastY = 0;
+  }, { passive: true });
+})();

muxplex/frontend/tests/test_terminal.mjs

@@ -5,6 +5,7 @@ import { test } from 'node:test';
 import assert from 'node:assert/strict';
 import { fileURLToPath } from 'node:url';
 import { dirname, join } from 'node:path';
+import fs from 'node:fs';
 
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = dirname(__filename);
@@ -717,3 +718,31 @@ test('terminal is auto-focused when WebSocket opens', () => {
   assert.strictEqual(t.focusCallCount, 1,
     '_term.focus() should be called exactly once when the WebSocket open event fires');
 });
+
+// --- Touch scroll source-inspection tests ---
+
+const terminalSrc = fs.readFileSync(
+  new URL('../terminal.js', import.meta.url), 'utf8'
+);
+
+test('terminal.js registers touchmove handler on terminal-container', () => {
+  // Source inspection: verify the touch scroll IIFE is present and uses
+  // e.preventDefault() (passive: false is required for prevent default)
+  assert.ok(terminalSrc.includes('touchmove'),
+    'touchmove listener must be present');
+  assert.ok(terminalSrc.includes('e.preventDefault'),
+    'must call preventDefault to prevent page scroll while swiping inside terminal');
+  assert.ok(terminalSrc.includes('scrollLines'),
+    'must call _term.scrollLines to scroll terminal');
+  assert.ok(terminalSrc.includes('passive: false'),
+    'touchmove must be non-passive to allow preventDefault');
+});
+
+test('terminal.js touchstart and touchend are passive', () => {
+  // touchstart and touchend should be passive: true for performance
+  // (they don't need preventDefault)
+  const touchstartPassive = terminalSrc.match(/touchstart[\s\S]*?passive:\s*(true|false)/);
+  const touchendPassive   = terminalSrc.match(/touchend[\s\S]*?passive:\s*(true|false)/);
+  assert.ok(touchstartPassive, 'touchstart listener must declare passive');
+  assert.ok(touchendPassive,   'touchend listener must declare passive');
+});

muxplex/tests/test_frontend_css.py

@@ -587,3 +587,20 @@ def test_mobile_active_tier_targets_tile_body_pre_not_tile_pre():
     assert ".session-tile--tier-active .tile-pre" not in css, (
         ".tile-pre is a dead class — selector must be removed"
     )
+
+
+def test_sidebar_list_has_touch_action_pan_y():
+    """Regression: without touch-action:pan-y .sidebar-list won't scroll on mobile touch.
+
+    Mobile browsers need an explicit touch-action:pan-y declaration to allow
+    vertical panning on an overflow-y:auto element when adjacent content (like
+    xterm.js canvas) may be consuming touch events.
+    """
+    css = read_css()
+    block = _extract_rule_block(css, ".sidebar-list {")
+    assert "touch-action: pan-y" in block, (
+        ".sidebar-list must have touch-action:pan-y for mobile vertical scroll"
+    )
+    assert "overscroll-behavior: contain" in block, (
+        ".sidebar-list must have overscroll-behavior:contain to prevent scroll chaining"
+    )