fix9-4: the mesh-wants wanted stream keeps each want's last word with no age limit

The generated contract is unchanged by seatgen (the keep is read from the definition).

Builds: design 47 G A-114 (§693, A-61)

modules/mesh-grants/internal/grants/wantedkeep_test.go

@@ -0,0 +1,32 @@
+package grants
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/seatdef"
+)
+
+// Design 47 G A-114 (§693, A-61): the seat mesh-wants' `wanted` stream keeps the last message of each subject with no age
+// limit, so each want's last word is read whole at a start.
+func TestWantedKeepsEachWantsLastWordWithNoAgeLimit(t *testing.T) {
+	raw, err := os.ReadFile(filepath.Join("..", "..", "..", "..", "contracts", "seats", "mesh-wants", "seat.json"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	d, err := seatdef.Parse(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, e := range d.Events {
+		if e.Name != "wanted" {
+			continue
+		}
+		if !e.KeptLastPerSubject() || e.KeptAgeDays() != 0 {
+			t.Errorf("wanted keeps last-per-subject %v for %d days, want true and 0 (no age limit)", e.KeptLastPerSubject(), e.KeptAgeDays())
+		}
+		return
+	}
+	t.Fatal("the seat mesh-wants has no event wanted")
+}