G A-38: HeldWriter.Held answers the findings it holds

Builds: design 47 G A-38, A-29

go/views/held_writer.go

@@ -98,3 +98,15 @@ func (h *HeldWriter[F, C, S, A]) WriteWire(ctx context.Context, finding map[stri
 	}
 	return h.Write(ctx, f)
 }
+
+// Held answers the findings the writer holds, a copy taken under its lock (design 47 G A-38), so a part reads its open findings
+// from the writer.
+func (h *HeldWriter[F, C, S, A]) Held() []F {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	out := make([]F, 0, len(h.held))
+	for _, f := range h.held {
+		out = append(out, f)
+	}
+	return out
+}

go/views/writer_test.go

@@ -514,6 +514,11 @@ func subHeldWriterStatesWhatItHoldsFromItsOwnState(t *testing.T) {
 		len(stated.Findings) != 2 || stated.Asked != "a1" {
 		t.Fatalf("the statement says %+v after %d events", stated, len(sent))
 	}
+	if held := h.Held(); len(held) != 2 {
+		t.Fatalf("Held answers %v", held)
+	} else if held[0].ID = "mutated"; len(h.Held()) != 2 {
+		t.Fatal("Held is not a copy")
+	}
 	ids := []string{stated.Findings[0].ID, stated.Findings[1].ID}
 	slices.Sort(ids)
 	if ids[0] != "raised" || ids[1] != "wired" {