fixup! util/vizerror: add new package for visible errors

Signed-off-by: Will Norris <will@tailscale.com>

tsweb/tsweb_test.go

@@ -21,6 +21,7 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"tailscale.com/metrics"
 	"tailscale.com/tstest"
+	"tailscale.com/util/vizerror"
 	"tailscale.com/version"
 )
 
@@ -151,6 +152,23 @@ func TestStdHandler(t *testing.T) {
 			},
 		},
 
+		{
+			name:     "handler returns user visible error",
+			rh:       handlerErr(0, vizerror.New("visible error")),
+			r:        req(bgCtx, "http://example.com/foo"),
+			wantCode: 500,
+			wantLog: AccessLogRecord{
+				When:       clock.Start,
+				Seconds:    1.0,
+				Proto:      "HTTP/1.1",
+				Host:       "example.com",
+				Method:     "GET",
+				RequestURI: "/foo",
+				Err:        "visible error",
+				Code:       500,
+			},
+		},
+
 		{
 			name:     "handler returns generic error",
 			rh:       handlerErr(0, testErr),