fix: rebuilds collect under one lock and keep moved lastmods

A rebuild takes the transaction-scoped advisory lock
golem15.sitemap.rebuild before it reads the settings and collects, and
applies in the same transaction, so a second rebuild collects only after
the first has committed. apply no longer writes the lastmod of a content
row it did not create, so a lastmod RecordSaved moved meanwhile stays.

filter_fixture_test.go

@@ -16,16 +16,34 @@ const filterPluginID = "acme.filter"
 
 // fakeFilter excludes addresses containing "noindex" (reason noindex) and
 // puts addresses containing "promo" into the group offers. It records the
-// batches it was asked.
+// batches it was asked; hook, when set, runs at the start of every Decide
+// (a test blocks a rebuild there).
 type fakeFilter struct {
 	mu      sync.Mutex
 	batches [][]contract.Candidate
+	hook    func()
+}
+
+// setHook sets the Decide hook for one test.
+func (f *fakeFilter) setHook(t interface{ Cleanup(func()) }, fn func()) {
+	f.mu.Lock()
+	f.hook = fn
+	f.mu.Unlock()
+	t.Cleanup(func() {
+		f.mu.Lock()
+		f.hook = nil
+		f.mu.Unlock()
+	})
 }
 
 func (f *fakeFilter) Decide(_ context.Context, batch []contract.Candidate) ([]contract.Decision, error) {
 	f.mu.Lock()
 	f.batches = append(f.batches, append([]contract.Candidate(nil), batch...))
+	hook := f.hook
 	f.mu.Unlock()
+	if hook != nil {
+		hook()
+	}
 	out := make([]contract.Decision, len(batch))
 	for i, c := range batch {
 		switch {