x/imagegen/transfer: fix timeout and progress reporting (#13679)

Removes 5-minute HTTP client timeout that caused "context deadline
exceeded" errors on large file downloads. Stall detection (10s)
already handles unresponsive connections.

Fixes progress bar total going down on resume by calculating total
from all blobs upfront and reporting already-downloaded bytes
as completed immediately.

x/imagegen/transfer/download.go

@@ -45,24 +45,33 @@ func download(ctx context.Context, opts DownloadOptions) error {
 		return nil
 	}
 
-	// Filter existing
-	var blobs []Blob
+	// Calculate total from all blobs (for accurate progress reporting on resume)
 	var total int64
+	for _, b := range opts.Blobs {
+		total += b.Size
+	}
+
+	// Filter out already-downloaded blobs and track completed bytes
+	var blobs []Blob
+	var alreadyCompleted int64
 	for _, b := range opts.Blobs {
 		if fi, _ := os.Stat(filepath.Join(opts.DestDir, digestToPath(b.Digest))); fi != nil && fi.Size() == b.Size {
 			if opts.Logger != nil {
 				opts.Logger.Debug("blob already exists", "digest", b.Digest, "size", b.Size)
 			}
+			alreadyCompleted += b.Size
 			continue
 		}
 		blobs = append(blobs, b)
-		total += b.Size
 	}
 	if len(blobs) == 0 {
 		return nil
 	}
 
 	token := opts.Token
+	progress := newProgressTracker(total, opts.Progress)
+	progress.add(alreadyCompleted) // Report already-downloaded bytes upfront
+
 	d := &downloader{
 		client:       cmp.Or(opts.Client, defaultClient),
 		baseURL:      opts.BaseURL,
@@ -72,7 +81,7 @@ func download(ctx context.Context, opts DownloadOptions) error {
 		getToken:     opts.GetToken,
 		userAgent:    cmp.Or(opts.UserAgent, defaultUserAgent),
 		stallTimeout: cmp.Or(opts.StallTimeout, defaultStallTimeout),
-		progress:     newProgressTracker(total, opts.Progress),
+		progress:     progress,
 		speeds:       &speedTracker{},
 		logger:       opts.Logger,
 	}

x/imagegen/transfer/transfer.go

@@ -110,8 +110,6 @@ var defaultClient = &http.Client{
 		MaxIdleConnsPerHost: 100,
 		IdleConnTimeout:     90 * time.Second,
 	},
-	Timeout: 5 * time.Minute,
-	// Don't follow redirects automatically - we handle them manually
 	CheckRedirect: func(req *http.Request, via []*http.Request) error {
 		return http.ErrUseLastResponse
 	},

x/imagegen/transfer/transfer_test.go

@@ -284,6 +284,83 @@ func TestDownloadSkipsExisting(t *testing.T) {
 	}
 }
 
+func TestDownloadResumeProgressTotal(t *testing.T) {
+	// Test that when resuming a download with some blobs already present:
+	// 1. Total reflects ALL blob sizes (not just remaining)
+	// 2. Completed starts at the size of already-downloaded blobs
+	serverDir := t.TempDir()
+	blob1, data1 := createTestBlob(t, serverDir, 1000)
+	blob2, data2 := createTestBlob(t, serverDir, 2000)
+	blob3, data3 := createTestBlob(t, serverDir, 3000)
+
+	// Pre-populate client with blob1 and blob2 (simulating partial download)
+	clientDir := t.TempDir()
+	for _, b := range []struct {
+		blob Blob
+		data []byte
+	}{{blob1, data1}, {blob2, data2}} {
+		path := filepath.Join(clientDir, digestToPath(b.blob.Digest))
+		if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(path, b.data, 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		digest := filepath.Base(r.URL.Path)
+		path := filepath.Join(serverDir, digestToPath(digest))
+		data, err := os.ReadFile(path)
+		if err != nil {
+			http.NotFound(w, r)
+			return
+		}
+		w.Header().Set("Content-Length", fmt.Sprintf("%d", len(data)))
+		w.WriteHeader(http.StatusOK)
+		w.Write(data)
+	}))
+	defer server.Close()
+
+	var firstCompleted, firstTotal int64
+	var gotFirstProgress bool
+	var mu sync.Mutex
+
+	err := Download(context.Background(), DownloadOptions{
+		Blobs:       []Blob{blob1, blob2, blob3},
+		BaseURL:     server.URL,
+		DestDir:     clientDir,
+		Concurrency: 1,
+		Progress: func(completed, total int64) {
+			mu.Lock()
+			defer mu.Unlock()
+			if !gotFirstProgress {
+				firstCompleted = completed
+				firstTotal = total
+				gotFirstProgress = true
+			}
+		},
+	})
+	if err != nil {
+		t.Fatalf("Download failed: %v", err)
+	}
+
+	// Total should be sum of ALL blobs, not just blob3
+	expectedTotal := blob1.Size + blob2.Size + blob3.Size
+	if firstTotal != expectedTotal {
+		t.Errorf("Total = %d, want %d (should include all blobs)", firstTotal, expectedTotal)
+	}
+
+	// First progress call should show already-completed bytes from blob1+blob2
+	expectedCompleted := blob1.Size + blob2.Size
+	if firstCompleted < expectedCompleted {
+		t.Errorf("First completed = %d, want >= %d (should include already-downloaded blobs)", firstCompleted, expectedCompleted)
+	}
+
+	// Verify blob3 was downloaded
+	verifyBlob(t, clientDir, blob3, data3)
+}
+
 func TestDownloadDigestMismatch(t *testing.T) {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		// Return wrong data