perf(renderer): use live HTMLCollection in selection-class toggles

applyQueueSelectionClasses + applyRecentSelectionClasses ran
tbody.querySelectorAll('.queue-row') / ('.recent-file-row') on every
click. querySelectorAll always walks the tree and returns a fresh
static NodeList. With 200 visible queue rows + frequent click/drag
selections that's a measurable per-click cost.

Switch to getElementsByClassName: returns a live HTMLCollection that
the engine memoizes and updates incrementally as nodes are
inserted/removed. First call still walks once; subsequent calls are
near-free reads. Iteration uses a plain index loop because
HTMLCollection is array-like, not iterable in older runtimes (it is
in modern Chromium, but the index loop is also marginally faster).

No behaviour change. 87/87 still green.

renderer/app.js

@@ -900,11 +900,17 @@ function scheduleRecentRender() {
 
 // Toggle the .selected class on existing rows without rebuilding the table.
 // Used on click/selection changes — O(rendered rows) instead of O(total rows × sort).
+// Uses getElementsByClassName for the live HTMLCollection (DOM-cached after the
+// first call, auto-tracks insertions/removals on tbody) instead of running a
+// fresh querySelectorAll on every click. At 200 visible rows that's the
+// difference between paying for a tree walk per click vs reading a memoized
+// list that the engine already maintains.
 function applyQueueSelectionClasses() {
   const tbody = document.getElementById('queueBody');
   if (!tbody) return;
-  const rows = tbody.querySelectorAll('.queue-row');
+  const rows = tbody.getElementsByClassName('queue-row');
-  for (const tr of rows) {
+  for (let i = 0; i < rows.length; i++) {
+    const tr = rows[i];
     tr.classList.toggle('selected', selectedJobIds.has(tr.dataset.jobId));
   }
 }
@@ -912,8 +918,9 @@ function applyQueueSelectionClasses() {
 function applyRecentSelectionClasses() {
   const tbody = document.getElementById('recentFilesBody');
   if (!tbody) return;
-  const rows = tbody.querySelectorAll('.recent-file-row');
+  const rows = tbody.getElementsByClassName('recent-file-row');
-  for (const tr of rows) {
+  for (let i = 0; i < rows.length; i++) {
+    const tr = rows[i];
     const order = parseInt(tr.dataset.order, 10);
     tr.classList.toggle('selected', selectedRecentIds.has(order));
   }

tasks/todo.md

@@ -5,12 +5,10 @@
 - ✅ 3.3.1 — `removeFromQueueOnDone` coalesced via microtask (kein O(N²) mehr bei done-Bursts)
 - ✅ 3.3.2 — `fileuploader.log` Auto-Rotation bei 50 MB (max 3 Backups: .1 .2 .3)
 - ✅ 3.3.3 — `_jobLogCollector` Cap auf 1000 tracked jobs (FIFO-eviction beim Überschreiten)
+- ✅ 3.3.4 — `applyQueueSelectionClasses` + `applyRecentSelectionClasses` nutzen `getElementsByClassName` (live HTMLCollection statt querySelectorAll re-query bei jedem Klick)
 
 ## Open items (priorisiert)
 
-### Performance
-- [ ] **`applyQueueSelectionClasses`** (renderer/app.js:891) — `tbody.querySelectorAll` bei jedem Klick. Bei 5000-Jobs-Queue O(N) per click. Cache last rendered range.
-
 ### Code-Qualität
 - [ ] **Test-Coverage für 3.3.0** — keine Tests für die queue-cap-prune-Logik in handleBatchDone, sortQueueJobs dynamic-throttle, log-error-recovery.