feat(tasks): run all queued tasks in parallel

Tasks are now started simultaneously when multiple are enqueued (e.g.
Run All). The worker drains all pending tasks at once and launches each
in its own goroutine, waiting via WaitGroup. kmsg watcher updated to
use a shared event window with a reference counter across concurrent tasks.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

audit/internal/webui/tasks.go

@@ -393,11 +393,13 @@ func (q *taskQueue) worker() {
 	for {
 		<-q.trigger
 		setCPUGovernor("performance")
+
+		// Drain all pending tasks and start them in parallel.
+		q.mu.Lock()
+		var batch []*Task
 		for {
-			q.mu.Lock()
 			t := q.nextPending()
 			if t == nil {
-				q.mu.Unlock()
 				break
 			}
 			now := time.Now()
@@ -406,37 +408,58 @@ func (q *taskQueue) worker() {
 			t.DoneAt = nil
 			t.ErrMsg = ""
 			j := newTaskJobState(t.LogPath)
-			ctx, cancel := context.WithCancel(context.Background())
-			j.cancel = cancel
 			t.job = j
+			batch = append(batch, t)
+		}
+		if len(batch) > 0 {
 			q.persistLocked()
-			q.mu.Unlock()
+		}
+		q.mu.Unlock()
 
-			if q.kmsgWatcher != nil && isSATTarget(t.Target) {
-				q.kmsgWatcher.NotifyTaskStarted(t.ID, t.Target)
-			}
+		var wg sync.WaitGroup
+		for _, t := range batch {
+			t := t
+			j := t.job
+			taskCtx, taskCancel := context.WithCancel(context.Background())
+			j.cancel = taskCancel
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
 
-			q.runTask(t, j, ctx)
-
-			if q.kmsgWatcher != nil {
-				q.kmsgWatcher.NotifyTaskFinished(t.ID)
-			}
-
-			q.mu.Lock()
-			now2 := time.Now()
-			t.DoneAt = &now2
-			if t.Status == TaskRunning { // not cancelled externally
-				if j.err != "" {
-					t.Status = TaskFailed
-					t.ErrMsg = j.err
-				} else {
-					t.Status = TaskDone
+				if q.kmsgWatcher != nil && isSATTarget(t.Target) {
+					q.kmsgWatcher.NotifyTaskStarted(t.ID, t.Target)
 				}
-			}
+
+				q.runTask(t, j, taskCtx)
+
+				if q.kmsgWatcher != nil {
+					q.kmsgWatcher.NotifyTaskFinished(t.ID)
+				}
+
+				q.mu.Lock()
+				now2 := time.Now()
+				t.DoneAt = &now2
+				if t.Status == TaskRunning {
+					if j.err != "" {
+						t.Status = TaskFailed
+						t.ErrMsg = j.err
+					} else {
+						t.Status = TaskDone
+					}
+				}
+				q.persistLocked()
+				q.mu.Unlock()
+			}()
+		}
+		wg.Wait()
+
+		if len(batch) > 0 {
+			q.mu.Lock()
 			q.prune()
 			q.persistLocked()
 			q.mu.Unlock()
 		}
+
 		setCPUGovernor("powersave")
 	}
 }