diff --git a/internal/artifact/reader_benchmark_test.go b/internal/artifact/reader_benchmark_test.go
new file mode 100644
index 0000000..39fa7cd
--- /dev/null
+++ b/internal/artifact/reader_benchmark_test.go
@@ -0,0 +1,167 @@
+package artifact
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha256"
+	"fmt"
+	"mime"
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+var artifactFileReadBenchmarkSink *domain.Artifact
+
+func BenchmarkArtifactFileRead(b *testing.B) {
+	for _, fixture := range makeArtifactReadBenchmarkFiles(b) {
+		b.Run(fixture.name, func(b *testing.B) {
+			reader := &fileReader{open: openArtifactFile}
+			ref := domain.ArtifactRef{Type: domain.ArtifactRefFile, URI: fixture.path}
+			checkArtifactFileRead(b, reader, ref, fixture.body)
+
+			b.ReportAllocs()
+			b.SetBytes(int64(len(fixture.body)))
+			b.ResetTimer()
+			for range b.N {
+				artifact, err := reader.Read(context.Background(), ref)
+				if err != nil {
+					b.Fatalf("read artifact: %v", err)
+				}
+				artifactFileReadBenchmarkSink = artifact
+			}
+			b.StopTimer()
+			runtime.KeepAlive(artifactFileReadBenchmarkSink)
+		})
+	}
+}
+
+// BenchmarkRetainedArtifactFileRead measures live artifact bodies when an
+// opened file reports a size larger than the content that reaches EOF.
+func BenchmarkRetainedArtifactFileRead(b *testing.B) {
+	body := bytes.Repeat([]byte("x"), 256<<10)
+	path := filepath.Join(b.TempDir(), "overreported.txt")
+	if err := os.WriteFile(path, body, 0o600); err != nil {
+		b.Fatal(err)
+	}
+	mime.TypeByExtension(filepath.Ext(path))
+
+	reader := &fileReader{open: func(path string) (artifactFile, error) {
+		file, err := os.Open(path)
+		if err != nil {
+			return nil, err
+		}
+		return &sizeReportingArtifactFile{artifactFile: file, reportedSize: 16 << 20}, nil
+	}}
+	ref := domain.ArtifactRef{Type: domain.ArtifactRefFile, URI: path}
+	checkArtifactFileRead(b, reader, ref, body)
+
+	const retainedBatchSize = 4
+	retained := make([]*domain.Artifact, retainedBatchSize)
+	artifactFileReadBenchmarkSink = nil
+	runtime.GC()
+	var setupMemory runtime.MemStats
+	runtime.ReadMemStats(&setupMemory)
+	runtime.KeepAlive(reader)
+	runtime.KeepAlive(ref)
+
+	b.ReportAllocs()
+	b.SetBytes(int64(len(body)))
+	b.ResetTimer()
+	for iteration := 0; iteration < b.N; iteration++ {
+		artifact, err := reader.Read(context.Background(), ref)
+		if err != nil {
+			b.Fatalf("read retained artifact: %v", err)
+		}
+		retained[iteration%len(retained)] = artifact
+	}
+	b.StopTimer()
+	for i, artifact := range retained {
+		if artifact != nil {
+			continue
+		}
+		artifact, err := reader.Read(context.Background(), ref)
+		if err != nil {
+			b.Fatalf("fill retained artifact batch: %v", err)
+		}
+		retained[i] = artifact
+	}
+	runtime.GC()
+	var retainedMemory runtime.MemStats
+	runtime.ReadMemStats(&retainedMemory)
+	b.ReportMetric(float64(int64(retainedMemory.HeapAlloc)-int64(setupMemory.HeapAlloc)), "retained-B")
+	runtime.KeepAlive(retained)
+	runtime.KeepAlive(reader)
+	runtime.KeepAlive(ref)
+}
+
+type artifactReadBenchmarkFile struct {
+	name string
+	path string
+	body []byte
+}
+
+func makeArtifactReadBenchmarkFiles(b *testing.B) []artifactReadBenchmarkFile {
+	b.Helper()
+	fixtures := []struct {
+		name string
+		size int
+	}{
+		{name: "small_4KiB", size: 4 << 10},
+		{name: "1MiB", size: 1 << 20},
+		{name: "large_4MiB", size: 4 << 20},
+	}
+	results := make([]artifactReadBenchmarkFile, 0, len(fixtures))
+	for _, fixture := range fixtures {
+		body := bytes.Repeat([]byte("x"), fixture.size)
+		path := filepath.Join(b.TempDir(), fixture.name+".txt")
+		if err := os.WriteFile(path, body, 0o600); err != nil {
+			b.Fatal(err)
+		}
+		mime.TypeByExtension(filepath.Ext(path))
+		results = append(results, artifactReadBenchmarkFile{
+			name: fixture.name,
+			path: path,
+			body: body,
+		})
+	}
+	return results
+}
+
+func checkArtifactFileRead(b *testing.B, reader Reader, ref domain.ArtifactRef, want []byte) {
+	b.Helper()
+	artifact, err := reader.Read(context.Background(), ref)
+	if err != nil {
+		b.Fatalf("check artifact read: %v", err)
+	}
+	if !bytes.Equal(artifact.Body, want) || artifact.Size != int64(len(want)) {
+		b.Fatalf("artifact size=%d body length=%d, want %d", artifact.Size, len(artifact.Body), len(want))
+	}
+	wantHash := fmt.Sprintf("%x", sha256.Sum256(want))
+	if artifact.Hash != wantHash {
+		b.Fatalf("artifact hash=%q, want %q", artifact.Hash, wantHash)
+	}
+}
+
+type sizeReportingArtifactFile struct {
+	artifactFile
+	reportedSize int64
+}
+
+func (file *sizeReportingArtifactFile) Stat() (os.FileInfo, error) {
+	info, err := file.artifactFile.Stat()
+	if err != nil {
+		return nil, err
+	}
+	return reportedArtifactFileInfo{FileInfo: info, size: file.reportedSize}, nil
+}
+
+type reportedArtifactFileInfo struct {
+	os.FileInfo
+	size int64
+}
+
+func (info reportedArtifactFileInfo) Size() int64 { return info.size }