feat(12-01): record multipart uploads and match Winter upload URLs

- attach.PublicURL and (*File).URL build Winter File::getPath() URLs; the
  thumbnailer decodes webp via golang.org/x/image v0.46.0 and checks the
  image size from the header before decoding
- tide requests carry multipart parts (files beside the fixture pinned by
  sha256) encoded with the fixed MultipartBoundary, so PHP and Go receive
  byte-identical bodies
- tide masks the random partition, disk name and file id of url/thumb_url
  upload URLs while still diffing prefix, size, mode and extension, and
  NormalizePublications masks Carbon dates in the published album

modules/lagoon/attach/url_test.go

@@ -0,0 +1,107 @@
+package attach
+
+import (
+	"bytes"
+	"image"
+	"image/jpeg"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"git.golem15.com/golem15/summercms/modules/compass"
+	"gocloud.dev/blob"
+)
+
+// winterLayoutBucket opens a mem:// bucket with the WinterCMS public prefix
+// and restores the framework default afterwards.
+func winterLayoutBucket(t *testing.T) *blob.Bucket {
+	t.Helper()
+	dir := t.TempDir()
+	body := "uploads:\n  bucket_url: \"mem://\"\n  public_path_prefix: \"/storage/app/uploads/public\"\n"
+	if err := os.WriteFile(filepath.Join(dir, "storage.yaml"), []byte(body), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := compass.Open(compass.Options{Dir: dir, Env: "development", Environ: []string{"SUMMER_ENV=development"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	bucket, err := OpenBucket(t.Context(), cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		_ = bucket.Close()
+		setPublicPathPrefix(defaultPublicPathPrefix)
+	})
+	return bucket
+}
+
+func TestFileURLWinterLayout(t *testing.T) {
+	bucket := winterLayoutBucket(t)
+	// A WinterCMS disk name: uniqid('', true) without the dot, plus the
+	// extension.
+	f := &File{ID: 12, DiskName: "651a2b3c4d5e61234567.png"}
+	if got, want := f.URL(), "/storage/app/uploads/public/651/a2b/3c4/651a2b3c4d5e61234567.png"; got != want {
+		t.Fatalf("URL = %q, want %q", got, want)
+	}
+	if got, want := PublicURL("/651/a2b/3c4/x.png"), "/storage/app/uploads/public/651/a2b/3c4/x.png"; got != want {
+		t.Fatalf("PublicURL = %q, want %q", got, want)
+	}
+	if err := bucket.WriteAll(t.Context(), BlobKey(f.DiskName), testJPEG(t), &blob.WriterOptions{ContentType: "image/png"}); err != nil {
+		t.Fatal(err)
+	}
+	thumb, err := f.Thumb(t.Context(), bucket, 200, 200, "crop")
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Winter getThumbFilename: implode('_', [thumb, id, w, h, ox, oy, mode.ext]).
+	if want := "/storage/app/uploads/public/651/a2b/3c4/thumb_12_200_200_0_0_crop.png"; thumb != want {
+		t.Fatalf("thumb = %q, want %q", thumb, want)
+	}
+	var nilFile *File
+	if nilFile.URL() != "" {
+		t.Fatal("nil file URL must be empty")
+	}
+}
+
+// webpFixture is a 16x12 lossless WebP: blue left half, red right half.
+var webpFixture = []byte{
+	0x52, 0x49, 0x46, 0x46, 0x2a, 0x00, 0x00, 0x00, 0x57, 0x45, 0x42, 0x50, 0x56, 0x50, 0x38, 0x4c,
+	0x1d, 0x00, 0x00, 0x00, 0x2f, 0x0f, 0xc0, 0x02, 0x00, 0x0f, 0x70, 0x14, 0xfb, 0x53, 0xd0, 0x5e,
+	0x88, 0x7b, 0xfe, 0x83, 0x07, 0x62, 0xc1, 0x64, 0xfe, 0xd2, 0xbd, 0x21, 0x44, 0xf4, 0x3f, 0x74,
+	0x01, 0x00,
+}
+
+func TestThumbWebP(t *testing.T) {
+	cfg, format, err := image.DecodeConfig(bytes.NewReader(webpFixture))
+	if err != nil {
+		t.Fatalf("DecodeConfig: %v", err)
+	}
+	if format != "webp" || cfg.Width != 16 || cfg.Height != 12 {
+		t.Fatalf("config = %s %dx%d", format, cfg.Width, cfg.Height)
+	}
+	bucket := winterLayoutBucket(t)
+	f := &File{ID: 5, DiskName: "abcdef123456789012345.webp"}
+	if err := bucket.WriteAll(t.Context(), BlobKey(f.DiskName), webpFixture, &blob.WriterOptions{ContentType: "image/webp"}); err != nil {
+		t.Fatal(err)
+	}
+	url, err := f.Thumb(t.Context(), bucket, 200, 200, "crop")
+	if err != nil {
+		t.Fatalf("Thumb: %v", err)
+	}
+	if want := "/storage/app/uploads/public/abc/def/123/thumb_5_200_200_0_0_crop.webp"; url != want {
+		t.Fatalf("thumb url = %q, want %q", url, want)
+	}
+	raw, err := bucket.ReadAll(t.Context(), "abc/def/123/thumb_5_200_200_0_0_crop.webp")
+	if err != nil {
+		t.Fatal(err)
+	}
+	// imaging cannot encode webp: the thumb is JPEG bytes under the .webp name.
+	img, err := jpeg.Decode(bytes.NewReader(raw))
+	if err != nil {
+		t.Fatalf("thumb is not JPEG: %v", err)
+	}
+	if b := img.Bounds(); b.Dx() != 200 || b.Dy() != 200 {
+		t.Fatalf("thumb size = %v", b)
+	}
+}