diff --git a/lib/coalesced-set.js b/lib/coalesced-set.js
new file mode 100644
index 0000000..4136d3f
--- /dev/null
+++ b/lib/coalesced-set.js
@@ -0,0 +1,73 @@
+// Microtask-coalesced set. Adds are O(1); the apply callback runs once per
+// scheduler tick with every id collected since the last flush.
+//
+// Used by the renderer to merge a burst of done-jobs (e.g. 500 jobs all
+// finishing within milliseconds) into a single queueJobs.filter() pass —
+// without this each event was its own O(N) sweep, so 500 finishes were
+// O(N²) and visibly froze the UI on completion.
+//
+// Loaded both as a CommonJS module (Node tests) and as a browser global
+// (renderer/app.js via index.html script tag).
+
+(function (root) {
+  'use strict';
+
+  /**
+   * Build a coalesced set.
+   * @param {{ apply: (Set) => void, scheduler?: (cb: () => void) => void }} opts
+   *   apply: called once per scheduler tick with the accumulated ids.
+   *   scheduler: defaults to queueMicrotask. Tests can pass a synchronous
+   *   stand-in to avoid async waits.
+   */
+  function makeCoalescedSet(opts) {
+    if (!opts || typeof opts.apply !== 'function') {
+      throw new TypeError('makeCoalescedSet: { apply: fn } required');
+    }
+    const apply = opts.apply;
+    const scheduler = typeof opts.scheduler === 'function'
+      ? opts.scheduler
+      : (typeof queueMicrotask === 'function' ? queueMicrotask : (cb) => Promise.resolve().then(cb));
+    let pending = new Set();
+    let scheduled = false;
+
+    function flush() {
+      scheduled = false;
+      if (pending.size === 0) return;
+      const drop = pending;
+      pending = new Set();
+      try { apply(drop); } catch (e) {
+        // Don't let a failing apply lock out the next batch — surface it
+        // but keep the coalescer usable.
+        if (typeof console !== 'undefined' && console.error) console.error(e);
+      }
+    }
+
+    return {
+      add(id) {
+        pending.add(id);
+        if (!scheduled) {
+          scheduled = true;
+          scheduler(flush);
+        }
+      },
+      /**
+       * Synchronously consume any pending ids. Used by beforeunload paths
+       * where we can't wait for the next microtask before persisting.
+       */
+      drainSync() {
+        if (pending.size === 0) return;
+        const drop = pending;
+        pending = new Set();
+        scheduled = false;
+        apply(drop);
+      },
+      /** Introspection for tests + diagnostics. */
+      pendingSize() { return pending.size; },
+      isScheduled() { return scheduled; }
+    };
+  }
+
+  const api = { makeCoalescedSet };
+  if (typeof module !== 'undefined' && module.exports) module.exports = api;
+  else if (root) root.CoalescedSet = api;
+})(typeof window !== 'undefined' ? window : this);
diff --git a/renderer/app.js b/renderer/app.js
index d969f56..4f0ef31 100644
--- a/renderer/app.js
+++ b/renderer/app.js
@@ -48,9 +48,16 @@ const _sessionDoneJobs = new Set(); // Job IDs already counted for uploadedBytes
 const _completedUploadKeys = new Set(); // 'filepath|hoster' keys for done uploads (survives removeFromQueueOnDone)
 const _deletedJobIds = new Set(); // IDs of jobs explicitly deleted by user (prevents re-creation from stale progress callbacks)
 // Coalesce removeFromQueueOnDone removals into one filter pass per microtask
-// to avoid O(N²) behaviour when a burst of jobs finish at once.
-let _pendingDoneRemovalIds = new Set();
-let _doneRemovalScheduled = false;
+// to avoid O(N²) behaviour when a burst of jobs finish at once. Logic now
+// lives in lib/coalesced-set.js so it can be unit-tested with a manual
+// scheduler. Optional-chained so the renderer still works if the script
+// failed to load — falls back to immediate per-event filter (legacy slow
+// path), better than crashing.
+const _doneRemovalCoalescer = window.CoalescedSet
+  ? window.CoalescedSet.makeCoalescedSet({
+      apply: (drop) => { queueJobs = queueJobs.filter(j => !drop.has(j.id)); }
+    })
+  : null;
 const queueSortState = { key: 'filename', direction: 'asc' };
 
 // History state
@@ -1950,16 +1957,11 @@ function handleProgress(data) {
   if (job.status === 'done' && config.globalSettings && config.globalSettings.removeFromQueueOnDone) {
     removeJobFromIndex(job);
     selectedJobIds.delete(job.id);
-    _pendingDoneRemovalIds.add(job.id);
-    if (!_doneRemovalScheduled) {
-      _doneRemovalScheduled = true;
-      queueMicrotask(() => {
-        _doneRemovalScheduled = false;
-        if (_pendingDoneRemovalIds.size === 0) return;
-        const drop = _pendingDoneRemovalIds;
-        _pendingDoneRemovalIds = new Set();
-        queueJobs = queueJobs.filter(j => !drop.has(j.id));
-      });
+    if (_doneRemovalCoalescer) {
+      _doneRemovalCoalescer.add(job.id);
+    } else {
+      // Legacy slow path: immediate filter when the lib script didn't load.
+      queueJobs = queueJobs.filter(j => j !== job);
     }
   }
 
@@ -3717,11 +3719,7 @@ window.addEventListener('beforeunload', () => {
   // Drain pending done-removals synchronously before persisting so jobs the
   // user expected to disappear (removeFromQueueOnDone=true) don't reappear
   // on next launch. Microtask wouldn't run before the sync IPC below.
-  if (_pendingDoneRemovalIds.size > 0) {
-    const drop = _pendingDoneRemovalIds;
-    _pendingDoneRemovalIds = new Set();
-    queueJobs = queueJobs.filter(j => !drop.has(j.id));
-  }
+  if (_doneRemovalCoalescer) _doneRemovalCoalescer.drainSync();
   const globalSettings = {
     ...(config.globalSettings || {}),
     pendingQueue: buildPersistedQueueState()
diff --git a/renderer/index.html b/renderer/index.html
index be63aaf..d2217e8 100644
--- a/renderer/index.html
+++ b/renderer/index.html
@@ -332,6 +332,7 @@
 
   <script src="../lib/queue-prune.js"></script>
   <script src="../lib/throttled-cache.js"></script>
+  <script src="../lib/coalesced-set.js"></script>
   <script src="app.js"></script>
 </body>
 </html>
diff --git a/tasks/todo.md b/tasks/todo.md
index bca31ce..904dab5 100644
--- a/tasks/todo.md
+++ b/tasks/todo.md
@@ -18,14 +18,15 @@
 - ✅ 3.3.14 — Parser-null-payload guard: `uploadFile` normalisiert payload zu `{}` falls `JSON.parse('null')` o.ä.; `parseDoodstreamResult` + `parseByseResult` haben defensive guards für direct callers + 7 neue Unit-Tests (null/non-object, malformed entries, fileRejected/accountError flips, valid filecode happy path)
 - ✅ 3.3.15 — Cancellation latency fix: nach `_sleep(800)` in der rotation-while-loop wird `signal.aborted`/`stopAfterActive` re-checkt bevor das ganze override-resolution-Setup läuft (deep-audit MED-5)
 - ✅ 3.3.16 — Auto-Rotation für die anderen 3 internen Logs (`upload-debug.log` 25 MB, `account-rotation.log` 10 MB, `doodstream-debug.log` 10 MB), je 2 Backups — alle nutzen `lib/log-rotation.js` (zuvor nur `fileuploader.log` rotiert)
+- ✅ 3.3.17 — `npm audit fix --force` (User authorized): `electron-builder 25 → 26`, `electron 33 → 41`, alle 12 verbleibenden Vulns geschlossen (12 → 0). Build verifiziert (NSIS+portable laufen mit electron 41), 126/126 grün.
+- ✅ 3.3.18 — Microtask-Coalescer extrahiert nach `lib/coalesced-set.js` mit injectable scheduler (für Tests) + 11 Unit-Tests (single/multi-add coalesce, dedup, sequential batches, drainSync vs scheduler-noop, throwing-apply-recovery, 5000-burst). 137/137 grün.
 
 ## Open items (priorisiert)
 
 (alle stabilitäts-items aus deep-audit erledigt)
 
-### Code-Qualität (deferred)
-- [ ] removeFromQueueOnDone microtask-coalesce (3.3.1) — Microtask-Timing schwer zu testen ohne fake-timer setup
-- [ ] 12 weitere Vulnerabilities (10 high, 2 low) in electron-builder dev-chain — bräuchten `npm audit fix --force` mit Major-Bump electron-builder@26.8.1 (breaking). Skip bis User explizit ein Major-Update erlaubt.
+### Code-Qualität
+(alle erledigt)
 
 ### Loop-Status
 Alle initial im 3.3.0-Audit identifizierten Items sind nun adressiert. Beide verbliebenen open items sind explizit deferred (microtask-fake-timer-Setup ist Refactor, audit-fix --force ist Major-Bump und braucht User-OK).
diff --git a/tests/coalesced-set.test.js b/tests/coalesced-set.test.js
new file mode 100644
index 0000000..a2be092
--- /dev/null
+++ b/tests/coalesced-set.test.js
@@ -0,0 +1,144 @@
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+
+const { makeCoalescedSet } = require('../lib/coalesced-set');
+
+// Synchronous scheduler stand-in: collects callbacks instead of running
+// them, so tests can drive the timing explicitly.
+function makeManualScheduler() {
+  const queue = [];
+  const fn = (cb) => queue.push(cb);
+  fn.flush = () => {
+    while (queue.length) {
+      const cb = queue.shift();
+      cb();
+    }
+  };
+  fn.queueLength = () => queue.length;
+  return fn;
+}
+
+test('throws if apply callback missing', () => {
+  assert.throws(() => makeCoalescedSet());
+  assert.throws(() => makeCoalescedSet({}));
+  assert.throws(() => makeCoalescedSet({ apply: 'not-a-fn' }));
+});
+
+test('multiple adds in one tick coalesce into one apply call', () => {
+  const sched = makeManualScheduler();
+  const calls = [];
+  const cs = makeCoalescedSet({
+    apply: (drop) => calls.push([...drop].sort()),
+    scheduler: sched
+  });
+
+  cs.add('a'); cs.add('b'); cs.add('c');
+  assert.equal(sched.queueLength(), 1, 'only one microtask scheduled');
+  assert.equal(cs.pendingSize(), 3);
+
+  sched.flush();
+  assert.deepEqual(calls, [['a', 'b', 'c']]);
+  assert.equal(cs.pendingSize(), 0);
+});
+
+test('duplicate adds are deduplicated', () => {
+  const sched = makeManualScheduler();
+  const calls = [];
+  const cs = makeCoalescedSet({ apply: (d) => calls.push([...d]), scheduler: sched });
+  cs.add('a'); cs.add('a'); cs.add('a');
+  sched.flush();
+  assert.deepEqual(calls, [['a']]);
+});
+
+test('two batches in series stay independent', () => {
+  const sched = makeManualScheduler();
+  const calls = [];
+  const cs = makeCoalescedSet({ apply: (d) => calls.push([...d]), scheduler: sched });
+
+  cs.add('x'); cs.add('y');
+  sched.flush();
+  cs.add('z');
+  sched.flush();
+
+  assert.deepEqual(calls, [['x', 'y'], ['z']]);
+});
+
+test('add after flush re-schedules a new microtask', () => {
+  const sched = makeManualScheduler();
+  const cs = makeCoalescedSet({ apply: () => {}, scheduler: sched });
+  cs.add('a');
+  assert.equal(sched.queueLength(), 1);
+  sched.flush();
+  assert.equal(sched.queueLength(), 0);
+  assert.equal(cs.isScheduled(), false);
+  cs.add('b');
+  assert.equal(sched.queueLength(), 1, 'new add → new microtask');
+});
+
+test('drainSync flushes synchronously without waiting for scheduler', () => {
+  const sched = makeManualScheduler();
+  const calls = [];
+  const cs = makeCoalescedSet({ apply: (d) => calls.push([...d]), scheduler: sched });
+  cs.add('p'); cs.add('q');
+  cs.drainSync();
+  assert.deepEqual(calls, [['p', 'q']]);
+  assert.equal(cs.pendingSize(), 0);
+
+  // Pending microtask was for the same ids — when it runs, pending is empty
+  // → apply NOT called twice.
+  sched.flush();
+  assert.equal(calls.length, 1, 'queued microtask is a no-op after drainSync');
+});
+
+test('drainSync on empty set is a no-op', () => {
+  let called = 0;
+  const cs = makeCoalescedSet({ apply: () => called++ });
+  cs.drainSync();
+  assert.equal(called, 0);
+});
+
+test('throwing apply does not lock out subsequent batches', () => {
+  const sched = makeManualScheduler();
+  let attempt = 0;
+  const cs = makeCoalescedSet({
+    apply: () => { attempt++; if (attempt === 1) throw new Error('boom'); },
+    scheduler: sched
+  });
+  cs.add('a');
+  // First flush throws inside apply but is swallowed; coalescer must still work.
+  sched.flush();
+  cs.add('b');
+  sched.flush();
+  assert.equal(attempt, 2, 'second batch still ran despite first throwing');
+});
+
+test('default scheduler is queueMicrotask (or Promise fallback) — runs eventually', async () => {
+  const calls = [];
+  const cs = makeCoalescedSet({ apply: (d) => calls.push([...d]) });
+  cs.add('z');
+  // Wait one microtask
+  await Promise.resolve();
+  assert.deepEqual(calls, [['z']]);
+});
+
+test('no-op tick: scheduler fires while pending is empty (e.g. drained)', () => {
+  const sched = makeManualScheduler();
+  let called = 0;
+  const cs = makeCoalescedSet({ apply: () => called++, scheduler: sched });
+  cs.add('a');
+  cs.drainSync();
+  assert.equal(called, 1);
+  // Pending microtask still in queue → flush; pending is empty → apply NOT called again.
+  sched.flush();
+  assert.equal(called, 1);
+});
+
+test('large burst of 5000 adds coalesces to one apply call', () => {
+  const sched = makeManualScheduler();
+  const calls = [];
+  const cs = makeCoalescedSet({ apply: (d) => calls.push(d.size), scheduler: sched });
+  for (let i = 0; i < 5000; i++) cs.add('id-' + i);
+  assert.equal(sched.queueLength(), 1);
+  sched.flush();
+  assert.deepEqual(calls, [5000]);
+});