diff --git a/static/style.css b/static/style.css
index dd9c8cbb..4e85c8e7 100644
--- a/static/style.css
+++ b/static/style.css
@@ -2728,6 +2728,8 @@
 /* ── Message action buttons (copy, edit, retry) ── */
 .msg-actions{display:flex;align-items:center;gap:2px;opacity:0;transition:opacity .15s;margin-left:auto;}
 .msg-row:hover .msg-actions{opacity:1;}
+.vscroll-measuring .msg-foot,
+.vscroll-measuring .msg-actions{transition:none !important;}
 .msg-action-btn{background:none;border:none;color:var(--muted);cursor:pointer;font-size:13px;padding:2px 5px;border-radius:5px;transition:color .12s,background .12s;line-height:1;}
 .msg-action-btn:hover{color:var(--accent-text);background:var(--accent-bg);}
 .selected-text-reply-btn{position:fixed;z-index:1200;display:inline-flex;align-items:center;gap:6px;padding:7px 11px;border:2px solid var(--accent);border-radius:999px;background:var(--bg);color:var(--text);box-shadow:0 8px 24px rgba(0,0,0,.26),0 0 0 1px var(--surface);font-size:12px;font-weight:700;line-height:1;cursor:pointer;opacity:0;pointer-events:none;transform:translateY(4px);transition:opacity .12s ease,transform .12s ease,background .12s ease,border-color .12s ease;user-select:none;}
diff --git a/static/ui.js b/static/ui.js
index 938b9857..1c9f759c 100644
--- a/static/ui.js
+++ b/static/ui.js
@@ -871,7 +871,8 @@ function _compensateScrollForMeasurementDelta(renderFn){
   if(!container) return renderFn();
   const anchorBefore=_captureMessageViewportAnchor();
   const scrollTopBefore=container.scrollTop;
-  renderFn();
+  container.classList.add('vscroll-measuring');
+  try{ renderFn(); }finally{ container.classList.remove('vscroll-measuring'); }
   if(!anchorBefore) return;
   if(scrollTopBefore<1){
     const spacer=container.querySelector('[data-virtual-spacer="before"]');
diff --git a/tests/test_issue4346_vscroll_footer_jitter.py b/tests/test_issue4346_vscroll_footer_jitter.py
new file mode 100644
index 00000000..5df5de07
--- /dev/null
+++ b/tests/test_issue4346_vscroll_footer_jitter.py
@@ -0,0 +1,50 @@
+"""Static source assertions for issue #4346 virtual-scroll footer jitter fix."""
+import pathlib
+import re
+
+ROOT = pathlib.Path(__file__).parent.parent
+
+CSS = (ROOT / 'static' / 'style.css').read_text(encoding='utf-8')
+JS  = (ROOT / 'static' / 'ui.js').read_text(encoding='utf-8')
+
+
+def test_css_vscroll_measuring_guard():
+    """style.css suppresses opacity transitions on .msg-foot and .msg-actions
+    while .vscroll-measuring is present on the scroll container."""
+    assert 'vscroll-measuring' in CSS
+    assert re.search(
+        r'\.vscroll-measuring\s+\.msg-foot.*transition\s*:\s*none\s*!important',
+        CSS, re.DOTALL
+    ), "missing transition:none !important for .vscroll-measuring .msg-foot"
+    assert re.search(
+        r'\.vscroll-measuring\s+\.msg-actions.*transition\s*:\s*none\s*!important',
+        CSS, re.DOTALL
+    ), "missing transition:none !important for .vscroll-measuring .msg-actions"
+
+
+def test_js_compensate_adds_vscroll_measuring():
+    """_compensateScrollForMeasurementDelta adds and removes the vscroll-measuring
+    class around the render callback."""
+    fn_match = re.search(
+        r'function _compensateScrollForMeasurementDelta\(renderFn\)\{(.+?)^(?=function )',
+        JS, re.DOTALL | re.MULTILINE
+    )
+    assert fn_match, "_compensateScrollForMeasurementDelta not found"
+    body = fn_match.group(1)
+    assert "classList.add('vscroll-measuring')" in body
+    assert "classList.remove('vscroll-measuring')" in body
+
+
+def test_js_try_finally_guards_class_removal():
+    """The classList.remove is in a finally block so the class is always cleared."""
+    fn_match = re.search(
+        r'function _compensateScrollForMeasurementDelta\(renderFn\)\{(.+?)^(?=function )',
+        JS, re.DOTALL | re.MULTILINE
+    )
+    assert fn_match
+    body = fn_match.group(1)
+    add_pos = body.find("classList.add('vscroll-measuring')")
+    try_pos = body.find('try{', add_pos) if add_pos != -1 else -1
+    finally_pos = body.find('finally{', try_pos) if try_pos != -1 else -1
+    remove_pos = body.find("classList.remove('vscroll-measuring')", finally_pos) if finally_pos != -1 else -1
+    assert remove_pos != -1, "classList.remove must be inside a finally block after classList.add"