Make remote publish locks generation-safe

internal/adapters/storage/object_store.go

@@ -2,10 +2,15 @@ package storage
 
 import (
 	"context"
+	"errors"
 	"io"
 	"time"
 )
 
+// ErrConditionNotMet reports that an object changed or already existed before a
+// conditional write could be committed.
+var ErrConditionNotMet = errors.New("object write condition not met")
+
 // ReaderUploader streams caller-owned, already-opened content to object storage.
 // Callers retain source-selection and filesystem-confinement policy.
 type ReaderUploader interface {
@@ -19,8 +24,10 @@ type ReaderUploader interface {
 // infer Narratio session semantics and do not prepend root prefixes.
 type ObjectStore interface {
 	List(ctx context.Context, prefix string) ([]ObjectInfo, error)
+	Read(ctx context.Context, key string) (ObjectInfo, io.ReadCloser, error)
 	Download(ctx context.Context, key, localPath string) error
 	Upload(ctx context.Context, localPath, key string, opts UploadOptions) (ObjectInfo, error)
+	UploadConditional(ctx context.Context, source io.Reader, key string, opts UploadOptions, condition WriteCondition) (ObjectInfo, error)
 	Exists(ctx context.Context, key string) (bool, error)
 }
 
@@ -37,3 +44,10 @@ type UploadOptions struct {
 	Metadata    map[string]string
 	ContentType string
 }
+
+// WriteCondition protects a mutable object update against a stale snapshot.
+// Exactly one condition is required by UploadConditional.
+type WriteCondition struct {
+	MatchETag     string
+	RequireAbsent bool
+}