Make remote publish locks generation-safe

docs/internal/storage.md

@@ -12,8 +12,10 @@ operator-selected storage fields and credential mechanisms belong in
 `storage.ObjectStore` interface:
 
 - `List(ctx, prefix)`
+- `Read(ctx, key)` returns an object body and the generation observed with it
 - `Download(ctx, key, localPath)`
 - `Upload(ctx, localPath, key, opts)`
+- `UploadConditional(ctx, source, key, opts, condition)`
 - `Exists(ctx, key)`
 
 Key invariant:
@@ -31,8 +33,13 @@ not own discovery, defaults, or configuration validation.
 
 - normalizes object keys.
 - `List` paginates and returns normalized `ObjectInfo`.
+- A truncated S3 listing must supply a new, non-empty continuation token;
+  otherwise listing fails with bucket and prefix context instead of looping.
 - `Download` writes local files with parent directory creation.
 - `Upload` streams local file and returns remote metadata.
+- `Read` binds a returned body to its S3 ETag. `UploadConditional` maps an ETag
+  match or absence precondition directly to the provider request and reports a
+  failed precondition without performing a local check-then-write replacement.
 - `Exists` maps not-found responses to `false`.
 
 ## Invariants