Test lower WebP and JPEG XL effort and the AVIF pixel limit

The WebP test now expects effort 2 instead of libvips' default of 4, a
new test expects JPEG XL at effort 4 instead of 7, and new tests expect an
AVIF output of more than 4096x4096 pixels to be refused before anything
is decoded and answered 400 on both image routes. They fail until the
settings and the refusal are in.

Model: opus-5-5

internal/handlers/avif_too_large_internal_test.go

@@ -0,0 +1,49 @@
+package handlers
+
+import (
+	"fmt"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// TestAVIFOutputTooLargeAnswers400 checks that respondImageError and
+// handleImageError, which answer the errors of the two image routes, answer
+// 400 naming the AVIF pixel limit when the image processor refuses an AVIF
+// output above it, wrapped as the service wraps it. The request's source only
+// goes into a log line, so it is left empty.
+func TestAVIFOutputTooLargeAnswers400(t *testing.T) {
+	t.Parallel()
+
+	h := &Handlers{log: slog.New(slog.DiscardHandler)}
+	err := fmt.Errorf("image processing failed: %w: 4097x4096",
+		imageprocessor.ErrAVIFOutputTooLarge)
+	wantBody := fmt.Sprintf("above %d pixels", imageprocessor.MaxAVIFOutputPixels)
+
+	plain := httptest.NewRecorder()
+	h.respondImageError(plain, &imgcache.ImageRequest{}, err)
+
+	encrypted := httptest.NewRecorder()
+	h.handleImageError(encrypted, err)
+
+	for name, rec := range map[string]*httptest.ResponseRecorder{
+		"respondImageError": plain, "handleImageError": encrypted,
+	} {
+		t.Logf("%s: status = %d, body = %q", name, rec.Code, rec.Body.String())
+
+		if rec.Code != http.StatusBadRequest {
+			t.Errorf("%s: status = %d, want %d",
+				name, rec.Code, http.StatusBadRequest)
+		}
+
+		if !strings.Contains(rec.Body.String(), wantBody) {
+			t.Errorf("%s: body = %q, want it to say %q",
+				name, rec.Body.String(), wantBody)
+		}
+	}
+}