Prevent stale content in Fast Render Mode

We do that by re-render visited pages that is not already in the stack. This may potentially do some double work, but that small penalty should be well worth it.

Fixes #5281

common/types/evictingqueue.go

@@ -52,6 +52,13 @@ func (q *EvictingStringQueue) Add(v string) {
 	q.mu.Unlock()
 }
 
+// Contains returns whether the queue contains v.
+func (q *EvictingStringQueue) Contains(v string) bool {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	return q.set[v]
+}
+
 // Peek looks at the last element added to the queue.
 func (q *EvictingStringQueue) Peek() string {
 	q.mu.Lock()

common/types/evictingqueue_test.go

@@ -36,6 +36,9 @@ func TestEvictingStringQueue(t *testing.T) {
 	queue.Add("a")
 	queue.Add("b")
 
+	assert.True(queue.Contains("a"))
+	assert.False(queue.Contains("foo"))
+
 	assert.Equal([]string{"b", "a"}, queue.PeekAll())
 	assert.Equal("b", queue.Peek())
 	queue.Add("c")