Add remote storage backend

internal/adapters/storage/factory.go

@@ -0,0 +1,29 @@
+package storage
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/config"
+)
+
+// NewObjectStoreFromConfig constructs a remote object store from resolved config.
+func NewObjectStoreFromConfig(ctx context.Context, cfg *config.Config) (ObjectStore, error) {
+	if cfg == nil || cfg.Pipeline == nil {
+		return nil, fmt.Errorf("pipeline config is required")
+	}
+
+	if strings.EqualFold(strings.TrimSpace(cfg.Pipeline.Storage.Backend), "s3") {
+		if cfg.Pipeline.Storage.S3 == nil {
+			return nil, fmt.Errorf("pipeline.storage.s3 is required when pipeline.storage.backend is s3")
+		}
+		return NewS3BackendFromConfig(ctx, *cfg.Pipeline.Storage.S3)
+	}
+
+	if cfg.Pipeline.Storage.S3 != nil && strings.TrimSpace(cfg.Pipeline.Storage.S3.Bucket) != "" {
+		return NewS3BackendFromConfig(ctx, *cfg.Pipeline.Storage.S3)
+	}
+
+	return nil, fmt.Errorf("no remote object store backend is configured")
+}

internal/adapters/storage/factory_test.go

@@ -0,0 +1,56 @@
+package storage
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/config"
+)
+
+func TestNewObjectStoreFromConfigBuildsS3WhenBackendIsS3(t *testing.T) {
+	original := newS3Client
+	t.Cleanup(func() { newS3Client = original })
+	newS3Client = func(_ context.Context, _ s3ClientOptions) (s3API, error) {
+		return &fakeS3API{}, nil
+	}
+
+	store, err := NewObjectStoreFromConfig(context.Background(), &config.Config{
+		Pipeline: &config.PipelineConfig{
+			Storage: config.StorageConfig{
+				Backend: "s3",
+				S3: &config.StorageS3Config{
+					Bucket: "my-archive",
+				},
+			},
+		},
+	})
+	if err != nil {
+		t.Fatalf("NewObjectStoreFromConfig() error = %v", err)
+	}
+	if _, ok := store.(*S3Backend); !ok {
+		t.Fatalf("store type = %T, want *S3Backend", store)
+	}
+}
+
+func TestNewObjectStoreFromConfigRequiresS3ConfigWhenBackendIsS3(t *testing.T) {
+	_, err := NewObjectStoreFromConfig(context.Background(), &config.Config{
+		Pipeline: &config.PipelineConfig{
+			Storage: config.StorageConfig{Backend: "s3"},
+		},
+	})
+	if err == nil || !strings.Contains(err.Error(), "pipeline.storage.s3 is required") {
+		t.Fatalf("NewObjectStoreFromConfig() error = %v, want missing storage.s3 error", err)
+	}
+}
+
+func TestNewObjectStoreFromConfigNoRemoteBackendConfigured(t *testing.T) {
+	_, err := NewObjectStoreFromConfig(context.Background(), &config.Config{
+		Pipeline: &config.PipelineConfig{
+			Storage: config.StorageConfig{Backend: "local"},
+		},
+	})
+	if err == nil || !strings.Contains(err.Error(), "no remote object store backend is configured") {
+		t.Fatalf("NewObjectStoreFromConfig() error = %v, want no-backend error", err)
+	}
+}

internal/adapters/storage/fake.go

@@ -1,6 +1,14 @@
 package storage
 
-import "context"
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"time"
+)
 
 // NoopBackend is a deterministic no-op archive/storage adapter.
 type NoopBackend struct{}
@@ -18,6 +26,13 @@ type FakeBackend struct {
 	Requests []ArchiveRequest
 	Err      error
 	Result   ArchiveResult
+
+	Objects map[string]FakeObject
+
+	ListErr     error
+	DownloadErr error
+	UploadErr   error
+	ExistsErr   error
 }
 
 // Archive records request and returns configured response.
@@ -38,3 +53,140 @@ func (f *FakeBackend) Archive(ctx context.Context, req ArchiveRequest) (ArchiveR
 	}
 	return res, nil
 }
+
+// FakeObject is a deterministic fake object-store record.
+type FakeObject struct {
+	Key          string
+	Data         []byte
+	Metadata     map[string]string
+	ETag         string
+	LastModified *time.Time
+}
+
+// SeedObject inserts or replaces an object in the fake object store.
+func (f *FakeBackend) SeedObject(obj FakeObject) {
+	if f.Objects == nil {
+		f.Objects = map[string]FakeObject{}
+	}
+	key := normalizeObjectKey(obj.Key)
+	obj.Key = key
+	obj.Data = append([]byte(nil), obj.Data...)
+	obj.Metadata = copyMetadata(obj.Metadata)
+	f.Objects[key] = obj
+}
+
+// List returns deterministic prefix-filtered objects.
+func (f *FakeBackend) List(ctx context.Context, prefix string) ([]ObjectInfo, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	if f.ListErr != nil {
+		return nil, f.ListErr
+	}
+
+	normalizedPrefix := normalizeObjectKey(prefix)
+	keys := make([]string, 0, len(f.Objects))
+	for key := range f.Objects {
+		if strings.HasPrefix(key, normalizedPrefix) {
+			keys = append(keys, key)
+		}
+	}
+	sort.Strings(keys)
+
+	out := make([]ObjectInfo, 0, len(keys))
+	for _, key := range keys {
+		obj := f.Objects[key]
+		out = append(out, ObjectInfo{
+			Key:          obj.Key,
+			Size:         int64(len(obj.Data)),
+			ETag:         obj.ETag,
+			LastModified: obj.LastModified,
+		})
+	}
+	return out, nil
+}
+
+// Download writes one object to a local path.
+func (f *FakeBackend) Download(ctx context.Context, key, localPath string) error {
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	if f.DownloadErr != nil {
+		return f.DownloadErr
+	}
+	if strings.TrimSpace(localPath) == "" {
+		return fmt.Errorf("download object: local path is required")
+	}
+
+	obj, ok := f.Objects[normalizeObjectKey(key)]
+	if !ok {
+		return fmt.Errorf("download object %q: %w", key, os.ErrNotExist)
+	}
+
+	if err := os.MkdirAll(filepath.Dir(localPath), 0o755); err != nil {
+		return fmt.Errorf("download object %q: create parent directory: %w", key, err)
+	}
+	if err := os.WriteFile(localPath, obj.Data, 0o644); err != nil {
+		return fmt.Errorf("download object %q: write local file: %w", key, err)
+	}
+	return nil
+}
+
+// Upload reads a local file and stores it under key.
+func (f *FakeBackend) Upload(ctx context.Context, localPath, key string, opts UploadOptions) (ObjectInfo, error) {
+	if err := ctx.Err(); err != nil {
+		return ObjectInfo{}, err
+	}
+	if f.UploadErr != nil {
+		return ObjectInfo{}, f.UploadErr
+	}
+	if strings.TrimSpace(localPath) == "" {
+		return ObjectInfo{}, fmt.Errorf("upload object: local path is required")
+	}
+	if strings.TrimSpace(key) == "" {
+		return ObjectInfo{}, fmt.Errorf("upload object: key is required")
+	}
+
+	data, err := os.ReadFile(localPath)
+	if err != nil {
+		return ObjectInfo{}, fmt.Errorf("upload object %q from %q: %w", key, localPath, err)
+	}
+
+	normalizedKey := normalizeObjectKey(key)
+	now := time.Now().UTC()
+	obj := FakeObject{
+		Key:          normalizedKey,
+		Data:         data,
+		Metadata:     copyMetadata(opts.Metadata),
+		LastModified: &now,
+	}
+	f.SeedObject(obj)
+	return ObjectInfo{
+		Key:          normalizedKey,
+		Size:         int64(len(data)),
+		LastModified: &now,
+	}, nil
+}
+
+// Exists checks object presence.
+func (f *FakeBackend) Exists(ctx context.Context, key string) (bool, error) {
+	if err := ctx.Err(); err != nil {
+		return false, err
+	}
+	if f.ExistsErr != nil {
+		return false, f.ExistsErr
+	}
+	_, ok := f.Objects[normalizeObjectKey(key)]
+	return ok, nil
+}
+
+func copyMetadata(in map[string]string) map[string]string {
+	if len(in) == 0 {
+		return nil
+	}
+	out := make(map[string]string, len(in))
+	for k, v := range in {
+		out[k] = v
+	}
+	return out
+}

internal/adapters/storage/fake_test.go

@@ -3,6 +3,9 @@ package storage
 import (
 	"context"
 	"errors"
+	"os"
+	"path/filepath"
+	"strings"
 	"testing"
 )
 
@@ -29,3 +32,84 @@ func TestFakeBackendError(t *testing.T) {
 		t.Fatal("expected error, got nil")
 	}
 }
+
+func TestFakeBackendListPrefixFiltering(t *testing.T) {
+	fake := &FakeBackend{}
+	fake.SeedObject(FakeObject{Key: "dnd/campaigns/forsaken/audio/a.flac", Data: []byte("a")})
+	fake.SeedObject(FakeObject{Key: "dnd/campaigns/forsaken/audio/b.flac", Data: []byte("b")})
+	fake.SeedObject(FakeObject{Key: "dnd/campaigns/other/audio/c.flac", Data: []byte("c")})
+
+	items, err := fake.List(context.Background(), "dnd/campaigns/forsaken/audio/")
+	if err != nil {
+		t.Fatalf("List() error = %v", err)
+	}
+	if len(items) != 2 {
+		t.Fatalf("List() len = %d, want 2", len(items))
+	}
+	if items[0].Key != "dnd/campaigns/forsaken/audio/a.flac" || items[1].Key != "dnd/campaigns/forsaken/audio/b.flac" {
+		t.Fatalf("List() keys = %#v", items)
+	}
+}
+
+func TestFakeBackendDownload(t *testing.T) {
+	fake := &FakeBackend{}
+	fake.SeedObject(FakeObject{Key: "audio/a.flac", Data: []byte("audio-a")})
+
+	dst := filepath.Join(t.TempDir(), "nested", "a.flac")
+	if err := fake.Download(context.Background(), "audio/a.flac", dst); err != nil {
+		t.Fatalf("Download() error = %v", err)
+	}
+	data, err := os.ReadFile(dst)
+	if err != nil {
+		t.Fatalf("ReadFile() error = %v", err)
+	}
+	if string(data) != "audio-a" {
+		t.Fatalf("downloaded content = %q, want %q", string(data), "audio-a")
+	}
+}
+
+func TestFakeBackendUploadAndExists(t *testing.T) {
+	fake := &FakeBackend{}
+
+	local := filepath.Join(t.TempDir(), "upload.txt")
+	if err := os.WriteFile(local, []byte("payload"), 0o644); err != nil {
+		t.Fatalf("WriteFile() error = %v", err)
+	}
+
+	info, err := fake.Upload(context.Background(), local, `runs\id\artifact.txt`, UploadOptions{
+		Metadata: map[string]string{"kind": "artifact"},
+	})
+	if err != nil {
+		t.Fatalf("Upload() error = %v", err)
+	}
+	if info.Key != "runs/id/artifact.txt" {
+		t.Fatalf("Upload() key = %q, want normalized key", info.Key)
+	}
+
+	ok, err := fake.Exists(context.Background(), "runs/id/artifact.txt")
+	if err != nil {
+		t.Fatalf("Exists() error = %v", err)
+	}
+	if !ok {
+		t.Fatal("Exists() = false, want true")
+	}
+}
+
+func TestFakeBackendObjectErrors(t *testing.T) {
+	fake := &FakeBackend{DownloadErr: errors.New("download fail"), UploadErr: errors.New("upload fail"), ListErr: errors.New("list fail"), ExistsErr: errors.New("exists fail")}
+
+	if _, err := fake.List(context.Background(), "x"); err == nil || !strings.Contains(err.Error(), "list fail") {
+		t.Fatalf("List() error = %v, want list fail", err)
+	}
+	if err := fake.Download(context.Background(), "x", filepath.Join(t.TempDir(), "x")); err == nil || !strings.Contains(err.Error(), "download fail") {
+		t.Fatalf("Download() error = %v, want download fail", err)
+	}
+	local := filepath.Join(t.TempDir(), "x.txt")
+	_ = os.WriteFile(local, []byte("x"), 0o644)
+	if _, err := fake.Upload(context.Background(), local, "x", UploadOptions{}); err == nil || !strings.Contains(err.Error(), "upload fail") {
+		t.Fatalf("Upload() error = %v, want upload fail", err)
+	}
+	if _, err := fake.Exists(context.Background(), "x"); err == nil || !strings.Contains(err.Error(), "exists fail") {
+		t.Fatalf("Exists() error = %v, want exists fail", err)
+	}
+}

internal/adapters/storage/keys.go

@@ -0,0 +1,8 @@
+package storage
+
+import "strings"
+
+func normalizeObjectKey(key string) string {
+	normalized := strings.ReplaceAll(strings.TrimSpace(key), "\\", "/")
+	return strings.TrimLeft(normalized, "/")
+}

internal/adapters/storage/keys_test.go

@@ -0,0 +1,21 @@
+package storage
+
+import "testing"
+
+func TestNormalizeObjectKey(t *testing.T) {
+	tests := []struct {
+		in   string
+		want string
+	}{
+		{in: `dnd\campaigns\forsaken\a.flac`, want: "dnd/campaigns/forsaken/a.flac"},
+		{in: " /dnd/campaigns/forsaken/a.flac ", want: "dnd/campaigns/forsaken/a.flac"},
+		{in: "//dnd/campaigns/forsaken/a.flac", want: "dnd/campaigns/forsaken/a.flac"},
+		{in: "", want: ""},
+	}
+
+	for _, tt := range tests {
+		if got := normalizeObjectKey(tt.in); got != tt.want {
+			t.Fatalf("normalizeObjectKey(%q) = %q, want %q", tt.in, got, tt.want)
+		}
+	}
+}

internal/adapters/storage/object_store.go

@@ -0,0 +1,32 @@
+package storage
+
+import (
+	"context"
+	"time"
+)
+
+// ObjectStore is a remote object storage boundary used by future prepare/archive work.
+//
+// Key invariant:
+// callers pass full bucket-relative object keys. Backend implementations do not
+// infer Narratio session semantics and do not prepend root prefixes.
+type ObjectStore interface {
+	List(ctx context.Context, prefix string) ([]ObjectInfo, error)
+	Download(ctx context.Context, key, localPath string) error
+	Upload(ctx context.Context, localPath, key string, opts UploadOptions) (ObjectInfo, error)
+	Exists(ctx context.Context, key string) (bool, error)
+}
+
+// ObjectInfo describes one object in remote storage.
+type ObjectInfo struct {
+	Key          string
+	Size         int64
+	ETag         string
+	LastModified *time.Time
+}
+
+// UploadOptions configures optional object upload metadata.
+type UploadOptions struct {
+	Metadata    map[string]string
+	ContentType string
+}

internal/adapters/storage/s3_backend.go

@@ -0,0 +1,241 @@
+package storage
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	awsconfig "github.com/aws/aws-sdk-go-v2/config"
+	"github.com/aws/aws-sdk-go-v2/service/s3"
+	"github.com/aws/aws-sdk-go-v2/service/s3/types"
+	"github.com/aws/smithy-go"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/config"
+)
+
+type s3API interface {
+	ListObjectsV2(ctx context.Context, params *s3.ListObjectsV2Input, optFns ...func(*s3.Options)) (*s3.ListObjectsV2Output, error)
+	GetObject(ctx context.Context, params *s3.GetObjectInput, optFns ...func(*s3.Options)) (*s3.GetObjectOutput, error)
+	PutObject(ctx context.Context, params *s3.PutObjectInput, optFns ...func(*s3.Options)) (*s3.PutObjectOutput, error)
+	HeadObject(ctx context.Context, params *s3.HeadObjectInput, optFns ...func(*s3.Options)) (*s3.HeadObjectOutput, error)
+}
+
+// S3Backend is an ObjectStore implementation backed by S3-compatible APIs.
+type S3Backend struct {
+	bucket string
+	client s3API
+}
+
+type s3ClientOptions struct {
+	Region         string
+	Endpoint       string
+	ForcePathStyle bool
+}
+
+var newS3Client = func(ctx context.Context, opts s3ClientOptions) (s3API, error) {
+	loadOpts := make([]func(*awsconfig.LoadOptions) error, 0, 1)
+	if strings.TrimSpace(opts.Region) != "" {
+		loadOpts = append(loadOpts, awsconfig.WithRegion(strings.TrimSpace(opts.Region)))
+	}
+	awsCfg, err := awsconfig.LoadDefaultConfig(ctx, loadOpts...)
+	if err != nil {
+		return nil, fmt.Errorf("load aws config: %w", err)
+	}
+
+	return s3.NewFromConfig(awsCfg, func(o *s3.Options) {
+		if strings.TrimSpace(opts.Endpoint) != "" {
+			endpoint := strings.TrimSpace(opts.Endpoint)
+			o.BaseEndpoint = &endpoint
+		}
+		o.UsePathStyle = opts.ForcePathStyle
+	}), nil
+}
+
+// NewS3BackendFromConfig builds an S3 backend from resolved config.
+func NewS3BackendFromConfig(ctx context.Context, cfg config.StorageS3Config) (*S3Backend, error) {
+	bucket := strings.TrimSpace(cfg.Bucket)
+	if bucket == "" {
+		return nil, fmt.Errorf("storage.s3.bucket is required")
+	}
+
+	client, err := newS3Client(ctx, s3ClientOptions{
+		Region:         cfg.Region,
+		Endpoint:       cfg.Endpoint,
+		ForcePathStyle: cfg.ForcePathStyle,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("build s3 client: %w", err)
+	}
+
+	return &S3Backend{
+		bucket: bucket,
+		client: client,
+	}, nil
+}
+
+// List returns objects under prefix.
+func (b *S3Backend) List(ctx context.Context, prefix string) ([]ObjectInfo, error) {
+	normalizedPrefix := normalizeObjectKey(prefix)
+	out := make([]ObjectInfo, 0)
+	var token *string
+
+	for {
+		resp, err := b.client.ListObjectsV2(ctx, &s3.ListObjectsV2Input{
+			Bucket:            &b.bucket,
+			Prefix:            &normalizedPrefix,
+			ContinuationToken: token,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("list objects under %q: %w", normalizedPrefix, err)
+		}
+
+		for _, item := range resp.Contents {
+			var lastModified *time.Time
+			if item.LastModified != nil {
+				t := *item.LastModified
+				lastModified = &t
+			}
+			out = append(out, ObjectInfo{
+				Key:          normalizeObjectKey(valueOrEmpty(item.Key)),
+				Size:         valueOrZeroInt64(item.Size),
+				ETag:         strings.Trim(valueOrEmpty(item.ETag), "\""),
+				LastModified: lastModified,
+			})
+		}
+
+		if !valueOrFalseBool(resp.IsTruncated) || resp.NextContinuationToken == nil {
+			break
+		}
+		token = resp.NextContinuationToken
+	}
+	return out, nil
+}
+
+// Download retrieves one object to localPath, creating parent directories as needed.
+func (b *S3Backend) Download(ctx context.Context, key, localPath string) error {
+	normalizedKey := normalizeObjectKey(key)
+	if strings.TrimSpace(localPath) == "" {
+		return fmt.Errorf("download object: local path is required")
+	}
+
+	resp, err := b.client.GetObject(ctx, &s3.GetObjectInput{
+		Bucket: &b.bucket,
+		Key:    &normalizedKey,
+	})
+	if err != nil {
+		return fmt.Errorf("download object %q: %w", normalizedKey, err)
+	}
+	defer resp.Body.Close()
+
+	if err := os.MkdirAll(filepath.Dir(localPath), 0o755); err != nil {
+		return fmt.Errorf("download object %q: create parent directory: %w", normalizedKey, err)
+	}
+	dst, err := os.Create(localPath)
+	if err != nil {
+		return fmt.Errorf("download object %q: create local file: %w", normalizedKey, err)
+	}
+	defer dst.Close()
+
+	if _, err := io.Copy(dst, resp.Body); err != nil {
+		return fmt.Errorf("download object %q: copy body: %w", normalizedKey, err)
+	}
+	if err := dst.Sync(); err != nil {
+		return fmt.Errorf("download object %q: sync local file: %w", normalizedKey, err)
+	}
+	return nil
+}
+
+// Upload sends a local file to key.
+func (b *S3Backend) Upload(ctx context.Context, localPath, key string, opts UploadOptions) (ObjectInfo, error) {
+	normalizedKey := normalizeObjectKey(key)
+	if strings.TrimSpace(localPath) == "" {
+		return ObjectInfo{}, fmt.Errorf("upload object: local path is required")
+	}
+	if normalizedKey == "" {
+		return ObjectInfo{}, fmt.Errorf("upload object: key is required")
+	}
+
+	file, err := os.Open(localPath)
+	if err != nil {
+		return ObjectInfo{}, fmt.Errorf("upload object %q from %q: %w", normalizedKey, localPath, err)
+	}
+	defer file.Close()
+
+	stat, err := file.Stat()
+	if err != nil {
+		return ObjectInfo{}, fmt.Errorf("upload object %q from %q: stat local file: %w", normalizedKey, localPath, err)
+	}
+
+	input := &s3.PutObjectInput{
+		Bucket:   &b.bucket,
+		Key:      &normalizedKey,
+		Body:     file,
+		Metadata: copyMetadata(opts.Metadata),
+	}
+	if strings.TrimSpace(opts.ContentType) != "" {
+		ct := strings.TrimSpace(opts.ContentType)
+		input.ContentType = &ct
+	}
+
+	resp, err := b.client.PutObject(ctx, input)
+	if err != nil {
+		return ObjectInfo{}, fmt.Errorf("upload object %q from %q: %w", normalizedKey, localPath, err)
+	}
+
+	return ObjectInfo{
+		Key:  normalizedKey,
+		Size: stat.Size(),
+		ETag: strings.Trim(valueOrEmpty(resp.ETag), "\""),
+	}, nil
+}
+
+// Exists checks whether one object key exists.
+func (b *S3Backend) Exists(ctx context.Context, key string) (bool, error) {
+	normalizedKey := normalizeObjectKey(key)
+	_, err := b.client.HeadObject(ctx, &s3.HeadObjectInput{
+		Bucket: &b.bucket,
+		Key:    &normalizedKey,
+	})
+	if err == nil {
+		return true, nil
+	}
+
+	var notFound *types.NotFound
+	if errors.As(err, &notFound) {
+		return false, nil
+	}
+	var apiErr smithy.APIError
+	if errors.As(err, &apiErr) {
+		switch apiErr.ErrorCode() {
+		case "NotFound", "NoSuchKey", "404":
+			return false, nil
+		}
+	}
+	return false, fmt.Errorf("head object %q: %w", normalizedKey, err)
+}
+
+func valueOrEmpty(v *string) string {
+	if v == nil {
+		return ""
+	}
+	return *v
+}
+
+func valueOrZeroInt64(v *int64) int64 {
+	if v == nil {
+		return 0
+	}
+	return *v
+}
+
+func valueOrFalseBool(v *bool) bool {
+	if v == nil {
+		return false
+	}
+	return *v
+}

internal/adapters/storage/s3_backend_test.go

@@ -0,0 +1,224 @@
+package storage
+
+import (
+	"context"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/aws/aws-sdk-go-v2/service/s3"
+	"github.com/aws/aws-sdk-go-v2/service/s3/types"
+	"github.com/aws/smithy-go"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/config"
+)
+
+type fakeS3API struct {
+	listOut *s3.ListObjectsV2Output
+	listErr error
+
+	getBody io.ReadCloser
+	getErr  error
+
+	putOut *s3.PutObjectOutput
+	putErr error
+
+	headErr error
+
+	lastList *s3.ListObjectsV2Input
+	lastGet  *s3.GetObjectInput
+	lastPut  *s3.PutObjectInput
+	lastHead *s3.HeadObjectInput
+}
+
+func (f *fakeS3API) ListObjectsV2(_ context.Context, params *s3.ListObjectsV2Input, _ ...func(*s3.Options)) (*s3.ListObjectsV2Output, error) {
+	f.lastList = params
+	if f.listErr != nil {
+		return nil, f.listErr
+	}
+	if f.listOut == nil {
+		return &s3.ListObjectsV2Output{}, nil
+	}
+	return f.listOut, nil
+}
+
+func (f *fakeS3API) GetObject(_ context.Context, params *s3.GetObjectInput, _ ...func(*s3.Options)) (*s3.GetObjectOutput, error) {
+	f.lastGet = params
+	if f.getErr != nil {
+		return nil, f.getErr
+	}
+	body := f.getBody
+	if body == nil {
+		body = io.NopCloser(strings.NewReader(""))
+	}
+	return &s3.GetObjectOutput{Body: body}, nil
+}
+
+func (f *fakeS3API) PutObject(_ context.Context, params *s3.PutObjectInput, _ ...func(*s3.Options)) (*s3.PutObjectOutput, error) {
+	f.lastPut = params
+	if f.putErr != nil {
+		return nil, f.putErr
+	}
+	if f.putOut == nil {
+		return &s3.PutObjectOutput{}, nil
+	}
+	return f.putOut, nil
+}
+
+func (f *fakeS3API) HeadObject(_ context.Context, params *s3.HeadObjectInput, _ ...func(*s3.Options)) (*s3.HeadObjectOutput, error) {
+	f.lastHead = params
+	if f.headErr != nil {
+		return nil, f.headErr
+	}
+	return &s3.HeadObjectOutput{}, nil
+}
+
+func TestS3BackendListAndKeyNormalization(t *testing.T) {
+	lastModified := time.Date(2026, 5, 16, 12, 0, 0, 0, time.UTC)
+	client := &fakeS3API{
+		listOut: &s3.ListObjectsV2Output{
+			Contents: []types.Object{
+				{Key: strPtr(`dnd\campaigns\forsaken\a.flac`), Size: int64Ptr(7), ETag: strPtr(`"abc"`), LastModified: &lastModified},
+			},
+		},
+	}
+	backend := &S3Backend{bucket: "bucket-1", client: client}
+
+	items, err := backend.List(context.Background(), `dnd\campaigns\`)
+	if err != nil {
+		t.Fatalf("List() error = %v", err)
+	}
+	if len(items) != 1 {
+		t.Fatalf("List() len = %d, want 1", len(items))
+	}
+	if items[0].Key != "dnd/campaigns/forsaken/a.flac" {
+		t.Fatalf("List() key = %q, want normalized slash key", items[0].Key)
+	}
+	if items[0].ETag != "abc" {
+		t.Fatalf("List() ETag = %q, want %q", items[0].ETag, "abc")
+	}
+	if client.lastList == nil || *client.lastList.Prefix != "dnd/campaigns/" {
+		t.Fatalf("List() prefix = %#v, want normalized prefix", client.lastList)
+	}
+}
+
+func TestS3BackendDownloadCreatesParentDirectory(t *testing.T) {
+	client := &fakeS3API{getBody: io.NopCloser(strings.NewReader("audio"))}
+	backend := &S3Backend{bucket: "bucket-1", client: client}
+
+	dst := filepath.Join(t.TempDir(), "nested", "clip.flac")
+	if err := backend.Download(context.Background(), `audio\clip.flac`, dst); err != nil {
+		t.Fatalf("Download() error = %v", err)
+	}
+
+	data, err := os.ReadFile(dst)
+	if err != nil {
+		t.Fatalf("ReadFile() error = %v", err)
+	}
+	if string(data) != "audio" {
+		t.Fatalf("downloaded content = %q, want %q", string(data), "audio")
+	}
+	if client.lastGet == nil || *client.lastGet.Key != "audio/clip.flac" {
+		t.Fatalf("GetObject key = %#v, want normalized key", client.lastGet)
+	}
+}
+
+func TestS3BackendUploadAndExists(t *testing.T) {
+	client := &fakeS3API{putOut: &s3.PutObjectOutput{ETag: strPtr(`"etag123"`)}}
+	backend := &S3Backend{bucket: "bucket-1", client: client}
+
+	local := filepath.Join(t.TempDir(), "artifact.txt")
+	if err := os.WriteFile(local, []byte("artifact"), 0o644); err != nil {
+		t.Fatalf("WriteFile() error = %v", err)
+	}
+
+	info, err := backend.Upload(context.Background(), local, `runs\id\artifact.txt`, UploadOptions{
+		Metadata: map[string]string{"kind": "artifact"},
+	})
+	if err != nil {
+		t.Fatalf("Upload() error = %v", err)
+	}
+	if info.Key != "runs/id/artifact.txt" {
+		t.Fatalf("Upload key = %q, want normalized key", info.Key)
+	}
+	if info.ETag != "etag123" {
+		t.Fatalf("Upload ETag = %q, want %q", info.ETag, "etag123")
+	}
+	if client.lastPut == nil || *client.lastPut.Key != "runs/id/artifact.txt" {
+		t.Fatalf("PutObject key = %#v, want normalized key", client.lastPut)
+	}
+
+	ok, err := backend.Exists(context.Background(), "runs/id/artifact.txt")
+	if err != nil {
+		t.Fatalf("Exists() error = %v", err)
+	}
+	if !ok {
+		t.Fatal("Exists() = false, want true")
+	}
+}
+
+func TestS3BackendUploadMissingLocalFile(t *testing.T) {
+	backend := &S3Backend{bucket: "bucket-1", client: &fakeS3API{}}
+	_, err := backend.Upload(context.Background(), filepath.Join(t.TempDir(), "missing.txt"), "key.txt", UploadOptions{})
+	if err == nil || !strings.Contains(err.Error(), "no such file") {
+		t.Fatalf("Upload() error = %v, want missing local file error", err)
+	}
+}
+
+func TestS3BackendExistsNotFound(t *testing.T) {
+	backend := &S3Backend{
+		bucket: "bucket-1",
+		client: &fakeS3API{
+			headErr: &smithy.GenericAPIError{Code: "NotFound", Message: "missing"},
+		},
+	}
+	ok, err := backend.Exists(context.Background(), "missing-key")
+	if err != nil {
+		t.Fatalf("Exists() error = %v", err)
+	}
+	if ok {
+		t.Fatal("Exists() = true, want false")
+	}
+}
+
+func TestNewS3BackendFromConfigUsesClientOptions(t *testing.T) {
+	original := newS3Client
+	t.Cleanup(func() { newS3Client = original })
+
+	var got s3ClientOptions
+	newS3Client = func(_ context.Context, opts s3ClientOptions) (s3API, error) {
+		got = opts
+		return &fakeS3API{}, nil
+	}
+
+	backend, err := NewS3BackendFromConfig(context.Background(), config.StorageS3Config{
+		Bucket:         "my-archive",
+		Region:         "us-east-1",
+		Endpoint:       "http://localhost:9000",
+		ForcePathStyle: true,
+	})
+	if err != nil {
+		t.Fatalf("NewS3BackendFromConfig() error = %v", err)
+	}
+	if backend.bucket != "my-archive" {
+		t.Fatalf("backend.bucket = %q, want %q", backend.bucket, "my-archive")
+	}
+	if got.Region != "us-east-1" || got.Endpoint != "http://localhost:9000" || !got.ForcePathStyle {
+		t.Fatalf("client options = %#v, want region/endpoint/path-style values", got)
+	}
+}
+
+func TestNewS3BackendFromConfigRequiresBucket(t *testing.T) {
+	_, err := NewS3BackendFromConfig(context.Background(), config.StorageS3Config{})
+	if err == nil || !strings.Contains(err.Error(), "bucket is required") {
+		t.Fatalf("NewS3BackendFromConfig() error = %v, want bucket validation", err)
+	}
+}
+
+func strPtr(v string) *string { return &v }
+func int64Ptr(v int64) *int64 { return &v }
+
+var _ s3API = (*fakeS3API)(nil)