diff --git a/frontend/packages/dashboard/src/app.js b/frontend/packages/dashboard/src/app.js
index 7056579c..a9847d3f 100644
--- a/frontend/packages/dashboard/src/app.js
+++ b/frontend/packages/dashboard/src/app.js
@@ -41,6 +41,28 @@ window.marked = marked;
 
   // Helpers ($, el, esc, form, fmtAgeSecs) moved to ./common.js (#406).
 
+  // #464 — atomic-swap render helper. Each managed section's render
+  // function used to do `root.innerHTML = ''; root.append(...);` in
+  // sequence; even though both operations sit in the same JS turn,
+  // operators could still see a "blink" on every poll cycle because
+  // (a) on async paths the await yield gave the browser a paint
+  // opportunity, and (b) complex builds with many `el()` allocations
+  // can blow the browser's per-task budget enough for layout to flash
+  // empty before the new children land.
+  //
+  // The fix: build the new content off-DOM into a `DocumentFragment`,
+  // then move it into the live root in a single `replaceChildren`
+  // call. The browser never sees an intermediate empty state. Builder
+  // callbacks receive the fragment as their `root` argument, so each
+  // renderer's existing `root.append(...)` code carries over with
+  // zero internal changes. Early-return inside the builder is fine —
+  // the commit still happens with whatever the builder appended.
+  function paintAtomic(liveRoot, build) {
+    const buf = document.createDocumentFragment();
+    build(buf);
+    liveRoot.replaceChildren(buf);
+  }
+
   // Side panel singleton (Panel) moved to ./common.js (#406).
 
   // Path linkification + file-preview side panel (openFilePanel,
@@ -1827,30 +1849,32 @@ window.marked = marked;
   // agents themselves and the operator already sees them next time
   // they interact with the page.
   async function refreshReminders() {
-    const root = $('reminders-section');
-    if (!root) return;
+    const liveRoot = $('reminders-section');
+    if (!liveRoot) return;
     try {
       const resp = await fetch('/api/reminders');
       if (!resp.ok) {
-        root.innerHTML = '';
-        root.append(el('p', { class: 'empty' }, 'reminders unavailable: http ' + resp.status));
+        paintAtomic(liveRoot, (root) => {
+          root.append(el('p', { class: 'empty' }, 'reminders unavailable: http ' + resp.status));
+        });
         return;
       }
       const rows = await resp.json();
       renderReminders(rows);
     } catch (err) {
-      root.innerHTML = '';
-      root.append(el('p', { class: 'empty' }, 'reminders fetch failed: ' + err));
+      paintAtomic(liveRoot, (root) => {
+        root.append(el('p', { class: 'empty' }, 'reminders fetch failed: ' + err));
+      });
     }
   }
   function renderReminders(rows) {
-    const root = $('reminders-section');
-    if (!root) return;
-    root.innerHTML = '';
-    if (!rows.length) {
-      root.append(el('p', { class: 'empty' }, 'no queued reminders'));
-      return;
-    }
+    const liveRoot = $('reminders-section');
+    if (!liveRoot) return;
+    paintAtomic(liveRoot, (root) => {
+      if (!rows.length) {
+        root.append(el('p', { class: 'empty' }, 'no queued reminders'));
+        return;
+      }
     const ul = el('ul', { class: 'reminders' });
     for (const r of rows) {
       const failed = (r.attempt_count || 0) > 0;
@@ -1910,6 +1934,7 @@ window.marked = marked;
       ul.append(li);
     }
     root.append(ul);
+    });  // paintAtomic
   }
   function fmtDuration(secs) {
     if (secs < 60) return secs + 's';
@@ -1939,14 +1964,16 @@ window.marked = marked;
     try {
       const resp = await fetch('/api/schedules');
       if (!resp.ok) {
-        listRoot.innerHTML = '';
-        listRoot.append(el('p', { class: 'empty' }, 'schedules unavailable: http ' + resp.status));
+        paintAtomic(listRoot, (root) => {
+          root.append(el('p', { class: 'empty' }, 'schedules unavailable: http ' + resp.status));
+        });
         return;
       }
       schedulesState = await resp.json();
     } catch (err) {
-      listRoot.innerHTML = '';
-      listRoot.append(el('p', { class: 'empty' }, 'schedules fetch failed: ' + err));
+      paintAtomic(listRoot, (root) => {
+        root.append(el('p', { class: 'empty' }, 'schedules fetch failed: ' + err));
+      });
       return;
     }
     renderScheduleNewForm();
@@ -2063,13 +2090,15 @@ window.marked = marked;
   }
 
   function renderScheduleNewForm() {
-    const root = $('schedule-new-section');
-    if (!root) return;
+    const liveRoot = $('schedule-new-section');
+    if (!liveRoot) return;
     // Preserve any field the operator was mid-typing in by reading
     // current values before we re-render. Only `body` + `description`
     // are big enough to feel — the others are toggle/datetime/number.
-    const carry = readScheduleFormCarry(root);
-    root.innerHTML = '';
+    // Read from the live root BEFORE the swap so we see current
+    // values (the fragment we build into is fresh).
+    const carry = readScheduleFormCarry(liveRoot);
+    paintAtomic(liveRoot, (root) => {
 
     // Targets multi-select pulls from the live containers list. The
     // backend accepts any string (forward-compat for richer recipients),
@@ -2165,6 +2194,7 @@ window.marked = marked;
     form_.append(actions);
 
     root.append(form_);
+    });  // paintAtomic
   }
   function readScheduleFormCarry(root) {
     return {
@@ -2249,23 +2279,24 @@ window.marked = marked;
     }
   }
   function renderSchedulesList() {
-    const root = $('schedules-section');
-    if (!root) return;
-    root.innerHTML = '';
-    if (!schedulesState.length) {
-      root.append(el('p', { class: 'empty' }, 'no schedules queued'));
-      return;
-    }
-    const ul = el('ul', { class: 'schedules' });
-    // Active schedules first (still firing), then cancelled tail.
-    const sorted = schedulesState.slice().sort((a, b) => {
-      const aDone = a.cancelled_at_unix ? 1 : 0;
-      const bDone = b.cancelled_at_unix ? 1 : 0;
-      if (aDone !== bDone) return aDone - bDone;
-      return a.next_fire_at_unix - b.next_fire_at_unix;
+    const liveRoot = $('schedules-section');
+    if (!liveRoot) return;
+    paintAtomic(liveRoot, (root) => {
+      if (!schedulesState.length) {
+        root.append(el('p', { class: 'empty' }, 'no schedules queued'));
+        return;
+      }
+      const ul = el('ul', { class: 'schedules' });
+      // Active schedules first (still firing), then cancelled tail.
+      const sorted = schedulesState.slice().sort((a, b) => {
+        const aDone = a.cancelled_at_unix ? 1 : 0;
+        const bDone = b.cancelled_at_unix ? 1 : 0;
+        if (aDone !== bDone) return aDone - bDone;
+        return a.next_fire_at_unix - b.next_fire_at_unix;
+      });
+      for (const s of sorted) ul.append(renderScheduleCard(s));
+      root.append(ul);
     });
-    for (const s of sorted) ul.append(renderScheduleCard(s));
-    root.append(ul);
   }
   function renderScheduleCard(s) {
     const cancelled = !!s.cancelled_at_unix;