A refusal coded method-not-found is ErrUnsupported: a row for it (issue 1966)

Claude-Session: https://claude.ai/code/session_01NcbgfFSnn24M3GcqttoU7i

go/state_test.go

@@ -222,6 +222,9 @@ func TestABundleKeepsAndWatchesStateThroughTheRuntime(t *testing.T) {
 	if !errors.Is(&refused{code: CodeChanged, message: "x"}, ErrChanged) {
 		t.Fatal("a refusal coded -32010 is not ErrChanged")
 	}
+	if !errors.Is(&refused{code: CodeNoMethod, message: "no mesh/state.page"}, errors.ErrUnsupported) || errors.Is(&refused{code: -32000}, errors.ErrUnsupported) {
+		t.Fatal("only a refusal coded -32601 is ErrUnsupported")
+	}
 	// Get of a key with no value is nil.
 	send(map[string]any{"jsonrpc": "2.0", "id": 3, "method": "tools/call", "params": map[string]any{"name": "recall",
 		"arguments": map[string]any{"key": "nothing"}}})