fix(memorypullcache): surface pull failures with the image ref

internal/memorypullcache/memorypullcache.go

@@ -135,12 +135,14 @@ func (c *MemoryPullCache) Fetch(ctx context.Context, ref string) (io.ReadCloser,
 
 	img, err := remote.Image(parsedRef, remoteOptions...)
 	if err != nil {
-		return nil, fmt.Errorf("in remote.Image: %w", err)
+		slog.WarnContext(ctx, "Image pull failed", slog.String("ref", ref), slog.Any("error", err))
+		return nil, fmt.Errorf("while pulling image %q: %w", ref, err)
 	}
 
 	size, err := img.Size()
 	if err != nil {
-		return nil, fmt.Errorf("in img.Size(): %w", err)
+		slog.WarnContext(ctx, "Image size lookup failed", slog.String("ref", ref), slog.Any("error", err))
+		return nil, fmt.Errorf("while reading size of image %q: %w", ref, err)
 	}
 	if size > 100*1024*1024 {
 		slog.InfoContext(ctx,
@@ -156,7 +158,8 @@ func (c *MemoryPullCache) Fetch(ctx context.Context, ref string) (io.ReadCloser,
 
 	memData, err := io.ReadAll(tarData)
 	if err != nil {
-		return nil, fmt.Errorf("while reading image: %w", err)
+		slog.WarnContext(ctx, "Image read failed", slog.String("ref", ref), slog.Any("error", err))
+		return nil, fmt.Errorf("while reading image %q: %w", ref, err)
 	}
 
 	if digestWasIncluded {

internal/memorypullcache/memorypullcache_test.go

@@ -15,6 +15,8 @@
 package memorypullcache
 
 import (
+	"context"
+	"strings"
 	"testing"
 )
 
@@ -82,3 +84,22 @@ func TestRewriteLocalRegistry(t *testing.T) {
 		})
 	}
 }
+
+// TestFetchErrorIncludesRef checks that pull failures wrap the error with the
+// requested image ref, so operators can identify which image failed from the
+// error chain alone (without having to correlate trace IDs across systems).
+func TestFetchErrorIncludesRef(t *testing.T) {
+	// A registry that refuses connection so remote.Image returns an error.
+	const ref = "127.0.0.1:1/missing/image:nope"
+	c, err := NewMemoryPullCache(context.Background(), nil, "")
+	if err != nil {
+		t.Fatalf("NewMemoryPullCache: %v", err)
+	}
+	_, err = c.Fetch(context.Background(), ref)
+	if err == nil {
+		t.Fatal("Fetch on an unreachable registry returned nil error")
+	}
+	if !strings.Contains(err.Error(), ref) {
+		t.Errorf("Fetch error %q does not contain ref %q", err, ref)
+	}
+}