claude-code: drop what was removed while away, render one at a time, refuse an empty settings set

Review of the nox-mesh plugin: a watch hands over what is there, not what
went, so the view is pruned to the state's keys before it starts; the
watches and the tools render one at a time, as the home's record is read
and written whole; the register answer names how an item is offered.

modules/claude-code/cmd/claude-code/config_test.go

@@ -318,3 +318,24 @@ func TestATreeIsTheSameOnlyWhenEveryFileAndModeIs(t *testing.T) {
 		t.Fatal("an extra file counted as the same")
 	}
 }
+
+// A registration removed while a node was away is dropped when it is back: the watch hands over only what is
+// there, so the view is pruned to the keys the state still holds.
+func TestWhatWasRemovedWhileANodeWasAwayIsDropped(t *testing.T) {
+	p, w := node(t, "laptop")
+	state, view := memConfig{}, NewConfigView(p)
+	for _, name := range []string{"kept", "gone"} {
+		if _, err := Register(p, Item{Kind: KindCommand, Name: name, Scope: ScopeMesh, Files: one(name, "x")}, nil, false, state, view, writer(w)); err != nil {
+			t.Fatal(err)
+		}
+	}
+	delete(state, "mesh.command.gone") // removed from another node while this one was off
+	back := NewConfigView(p)           // the node starts again from what it last wrote
+	if len(back.Items()) != 2 {
+		t.Fatalf("the view did not start from what was last written: %v", back.Items())
+	}
+	keys, _ := state.Keys()
+	if !back.Prune(keys) || len(back.Items()) != 1 {
+		t.Fatalf("after pruning: %v", back.Items())
+	}
+}