p3: tavily parse errors degrade; retry DNS on search

A 200 with a bad Tavily body is tavily: error, not an empty success
that would cache for the hour. Upstream clients stay in the source
list if DNS is down at boot and retry the pin on Search; /healthz
lists them as unresolved until a pin lands.

internal/search/sources_test.go

@@ -95,3 +95,21 @@ func TestBraveMapsSources(t *testing.T) {
 		t.Fatal("grounding used as snippet")
 	}
 }
+
+func TestTavilyBadJSONIsError(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = w.Write([]byte(`not-json`))
+	}))
+	defer ts.Close()
+	c, err := dial.New(ts.URL, dial.Options{Loopback: true, Timeout: time.Second})
+	if err != nil {
+		t.Fatal(err)
+	}
+	out := (&Tavily{Client: c, Key: "k"}).Search(context.Background(), "q", 5)
+	if out.Warn != "tavily: error" {
+		t.Fatalf("warn %q", out.Warn)
+	}
+	if len(out.Hits) != 0 || out.Credits != 0 {
+		t.Fatalf("%+v", out)
+	}
+}