fix: bound opening a Chrome tab

Render bounds opening the tab and rendering the page with one deadline
(TabOpenTimeout 5 s plus RenderTimeout 20 s), so a hung Chrome no longer
holds the crawl's render lock until the job timeout.

classes/crawl/render_test.go

@@ -8,6 +8,7 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 
 	"git.golem15.com/golem15/summercms/modules/compass"
 )
@@ -124,3 +125,42 @@ func TestRenderMax(t *testing.T) {
 		t.Fatalf("SiteHosts = %v", got)
 	}
 }
+
+// TestRenderTabTimeout pins L3 WR-06: a tab that does not open answers an
+// error within TabOpenTimeout (lowered for the test) plus a margin, so the
+// crawl's render lock is released; the next Render is not held up by the
+// first one's hung tab.
+func TestRenderTabTimeout(t *testing.T) {
+	saved := TabOpenTimeout
+	TabOpenTimeout = 50 * time.Millisecond
+	t.Cleanup(func() { TabOpenTimeout = saved })
+	hung := make(chan struct{})
+	t.Cleanup(func() { close(hung) })
+	r := &chromeRenderer{
+		allowed:    []string{"example.test"},
+		browserCtx: context.Background(),
+		newTab: func(parent context.Context) (context.Context, context.CancelFunc) {
+			return context.WithCancel(parent)
+		},
+		// A hung Chrome: opening the tab never answers, even when the tab
+		// is closed.
+		startTab: func(context.Context) error {
+			<-hung
+			return nil
+		},
+	}
+	for i := range 2 {
+		start := time.Now()
+		_, err := r.Render(t.Context(), "https://example.test/a")
+		if err == nil || !strings.Contains(err.Error(), "did not open a tab within 50ms") {
+			t.Fatalf("Render %d: %v, want the tab timeout", i, err)
+		}
+		if d := time.Since(start); d > time.Second {
+			t.Fatalf("Render %d returned after %v", i, d)
+		}
+	}
+	TabOpenTimeout = 5 * time.Second
+	if got := seconds(TabOpenTimeout); got != "5 s" {
+		t.Fatalf("seconds = %q", got)
+	}
+}