diff --git a/src/StorageAccessor/DirectVault.ts b/src/StorageAccessor/DirectVault.ts
index d3e67ec..9ee770a 100644
--- a/src/StorageAccessor/DirectVault.ts
+++ b/src/StorageAccessor/DirectVault.ts
@@ -1,6 +1,6 @@
-import type { Stat } from "obsidian";
-import { FileType, StorageAccessorTypes } from "../storage.ts";
+import { normalizePath, type Stat } from "obsidian";
 import { StorageAccessor } from "./StorageAccessor.ts";
+import { FileType, StorageAccessorTypes } from "./storage-accessor-types.ts";
 
 
 export class DirectVault extends StorageAccessor {
@@ -8,6 +8,10 @@ export class DirectVault extends StorageAccessor {
 
     sep = "/"; // Always use / as separator on vault.
 
+    normalizePath(path: string): string {
+        return normalizePath(path);
+    }
+
     async createFolder(absolutePath: string): Promise<void> {
         await this.app.vault.adapter.mkdir(absolutePath);
     }
diff --git a/src/StorageAccessor/ExternalVaultFilesystem.test.ts b/src/StorageAccessor/ExternalVaultFilesystem.test.ts
new file mode 100644
index 0000000..3617068
--- /dev/null
+++ b/src/StorageAccessor/ExternalVaultFilesystem.test.ts
@@ -0,0 +1,36 @@
+// eslint-disable-next-line import/no-nodejs-modules -- Electron file reads return Node Buffers.
+import { Buffer } from "node:buffer";
+import { ExternalVaultFilesystem } from "./ExternalVaultFilesystem.ts";
+import type { StorageAccessorHost } from "./storage-accessor-types.ts";
+
+declare const Deno: {
+    test: (name: string, fn: () => void | Promise<void>) => void;
+};
+
+function assertEquals<T>(actual: T, expected: T, message: string) {
+    if (JSON.stringify(actual) !== JSON.stringify(expected)) {
+        throw new Error(`${message}\nactual=${JSON.stringify(actual)}\nexpected=${JSON.stringify(expected)}`);
+    }
+}
+
+Deno.test("ExternalVaultFilesystem: reads only the visible Node Buffer bytes", async () => {
+    const backing = Buffer.from([99, 1, 2, 3, 88]);
+    const visible = backing.subarray(1, 4);
+    const plugin = {
+        app: {
+            vault: {
+                adapter: {
+                    fsPromises: {
+                        readFile: async () => visible,
+                    },
+                },
+            },
+        },
+    } as unknown as StorageAccessorHost;
+    const storage = new ExternalVaultFilesystem(plugin);
+
+    const result = await storage._readBinary("archive.bin");
+    if (result === false) throw new Error("Expected binary data");
+
+    assertEquals([...new Uint8Array(result)], [1, 2, 3], "Buffer byte offset and length should be preserved");
+});
diff --git a/src/StorageAccessor/ExternalVaultFilesystem.ts b/src/StorageAccessor/ExternalVaultFilesystem.ts
index cfed4f5..ad7b0b5 100644
--- a/src/StorageAccessor/ExternalVaultFilesystem.ts
+++ b/src/StorageAccessor/ExternalVaultFilesystem.ts
@@ -1,8 +1,11 @@
 import type { Stat } from "obsidian";
-import { type FsAPI, FileType, StorageAccessorTypes } from "../storage.ts";
+// eslint-disable-next-line import/no-nodejs-modules -- Electron exposes the Node filesystem API used here.
+import type { promises } from "node:fs";
 import { StorageAccessor } from "./StorageAccessor.ts";
+import { FileType, StorageAccessorTypes } from "./storage-accessor-types.ts";
 import { toArrayBuffer } from "../util.ts";
 
+type FsAPI = Pick<typeof promises, "mkdir" | "writeFile" | "readFile" | "stat" | "rm">;
 
 export class ExternalVaultFilesystem extends StorageAccessor {
     type = StorageAccessorTypes.EXTERNAL;
@@ -21,7 +24,7 @@ export class ExternalVaultFilesystem extends StorageAccessor {
         await this.fsPromises.mkdir(absolutePath, { recursive: true });
     }
 
-    async ensureDirectory(fullPath: string) {
+    override async ensureDirectory(fullPath: string) {
         const delimiter = this.sep;
         const pathElements = fullPath.split(delimiter);
         pathElements.pop();
@@ -42,7 +45,7 @@ export class ExternalVaultFilesystem extends StorageAccessor {
 
     async _readBinary(path: string): Promise<ArrayBuffer | false> {
         const buffer = await this.fsPromises.readFile(path);
-        return toArrayBuffer(buffer.buffer)
+        return toArrayBuffer(buffer);
     }
 
     async deleteBinary(path: string): Promise<boolean> {
diff --git a/src/StorageAccessor/NormalVault.ts b/src/StorageAccessor/NormalVault.ts
index 7298b42..a82dff1 100644
--- a/src/StorageAccessor/NormalVault.ts
+++ b/src/StorageAccessor/NormalVault.ts
@@ -1,6 +1,6 @@
-import { TFile, TFolder, type Stat } from "obsidian";
-import { FileType, StorageAccessorTypes } from "../storage.ts";
+import { normalizePath, TFile, TFolder, type Stat } from "obsidian";
 import { StorageAccessor } from "./StorageAccessor.ts";
+import { FileType, StorageAccessorTypes } from "./storage-accessor-types.ts";
 
 
 export class NormalVault extends StorageAccessor {
@@ -8,6 +8,10 @@ export class NormalVault extends StorageAccessor {
 
     sep = "/"; // Always use / as separator on vault.
 
+    normalizePath(path: string): string {
+        return normalizePath(path);
+    }
+
     async createFolder(absolutePath: string): Promise<void> {
         await this.app.vault.createFolder(absolutePath);
     }
diff --git a/src/StorageAccessor/S3Bucket.ts b/src/StorageAccessor/S3Bucket.ts
index 2c40f3e..63e4ea3 100644
--- a/src/StorageAccessor/S3Bucket.ts
+++ b/src/StorageAccessor/S3Bucket.ts
@@ -1,8 +1,8 @@
 import { S3 } from "@aws-sdk/client-s3";
-import type { Stat } from "obsidian";
+import { normalizePath, type Stat } from "obsidian";
 import { ObsHttpHandler } from "../ObsHttpHandler.ts";
-import { FileType, StorageAccessorTypes } from "../storage.ts";
 import { StorageAccessor } from "./StorageAccessor.ts";
+import { FileType, StorageAccessorTypes } from "./storage-accessor-types.ts";
 import { toArrayBuffer } from "../util.ts";
 
 
@@ -10,11 +10,15 @@ export class S3Bucket extends StorageAccessor {
     type = StorageAccessorTypes.S3;
     sep = "/";
 
+    normalizePath(path: string): string {
+        return normalizePath(path);
+    }
+
     createFolder(absolutePath: string): Promise<void> {
         // S3 does not have folder concept. So, we don't need to create folder.
         return Promise.resolve();
     }
-    ensureDirectory(fullPath: string): Promise<void> {
+    override ensureDirectory(fullPath: string): Promise<void> {
         return Promise.resolve();
     }
 
diff --git a/src/StorageAccessor/StorageAccessor.ts b/src/StorageAccessor/StorageAccessor.ts
index a0619ae..2fd4231 100644
--- a/src/StorageAccessor/StorageAccessor.ts
+++ b/src/StorageAccessor/StorageAccessor.ts
@@ -1,13 +1,19 @@
-import { normalizePath, type Stat } from "obsidian";
-import type DiffZipBackupPlugin from "../../main.ts";
-import { type StorageAccessorType, FileType, decryptCompatOpenSSL, encryptCompatOpenSSL } from "../storage.ts";
+import type { Stat } from "obsidian";
+import { OpenSSLCompat } from "octagonal-wheels/encryption";
+import {
+    type StorageAccessorHost,
+    type StorageAccessorType,
+    FileType,
+} from "./storage-accessor-types.ts";
 import { toArrayBuffer } from "../util.ts";
 
+const decryptCompatOpenSSL = OpenSSLCompat.CBC.decryptCBC;
+const encryptCompatOpenSSL = OpenSSLCompat.CBC.encryptCBC;
 
 export abstract class StorageAccessor {
     abstract type: StorageAccessorType;
     abstract sep: string;
-    public plugin: DiffZipBackupPlugin;
+    public plugin: StorageAccessorHost;
     get app() {
         return this.plugin.app;
     }
@@ -21,7 +27,7 @@ export abstract class StorageAccessor {
     }
     public isLocal: boolean = false;
 
-    constructor(plugin: DiffZipBackupPlugin, basePath?: string, isLocal?: boolean) {
+    constructor(plugin: StorageAccessorHost, basePath?: string, isLocal?: boolean) {
         this.basePath = basePath || "";
         this.plugin = plugin;
         this.isLocal = isLocal || false;
@@ -73,9 +79,7 @@ export abstract class StorageAccessor {
     abstract _readBinary(path: string, preventUseCache?: boolean): Promise<ArrayBuffer | false>;
     abstract deleteBinary(path: string): Promise<boolean>;
 
-    normalizePath(path: string): string {
-        return normalizePath(path);
-    }
+    abstract normalizePath(path: string): string;
     abstract stat(path: string): Promise<false | Stat>;
 
     async ensureDirectory(fullPath: string) {
diff --git a/src/StorageAccessor/storage-accessor-types.ts b/src/StorageAccessor/storage-accessor-types.ts
new file mode 100644
index 0000000..723e4ec
--- /dev/null
+++ b/src/StorageAccessor/storage-accessor-types.ts
@@ -0,0 +1,30 @@
+import type { App } from "obsidian";
+import type { DiffZipBackupSettings } from "../types.ts";
+
+/**
+ * DiffZip-owned context supplied to storage accessor implementations.
+ *
+ * This is an internal composition shape, not a platform-neutral storage contract.
+ */
+export interface StorageAccessorHost {
+    readonly app: App;
+    readonly settings: DiffZipBackupSettings;
+}
+
+/** File kind reported by a storage accessor. */
+export enum FileType {
+    Missing,
+    File,
+    Folder,
+}
+
+/** Stable storage accessor identifiers. */
+export const StorageAccessorTypes = {
+    NORMAL: "normal",
+    DIRECT: "direct",
+    EXTERNAL: "external",
+    S3: "s3",
+} as const;
+
+/** Identifier for one DiffZip storage accessor implementation. */
+export type StorageAccessorType = typeof StorageAccessorTypes[keyof typeof StorageAccessorTypes];
diff --git a/src/storage.ts b/src/storage.ts
index ba3a7ce..9316d8d 100644
--- a/src/storage.ts
+++ b/src/storage.ts
@@ -2,40 +2,21 @@
  * Abstract class for storage accessors and its implementations.
  */
 import type DiffZipBackupPlugin from "../main.ts";
-// Because of this is a type-only import.
-// eslint-disable-next-line import/no-nodejs-modules -- type only import of promises
-import type { promises } from "node:fs";
-import { OpenSSLCompat } from "octagonal-wheels/encryption";
 import { NormalVault } from "./StorageAccessor/NormalVault.ts";
 import { DirectVault } from "./StorageAccessor/DirectVault.ts";
 import { ExternalVaultFilesystem } from "./StorageAccessor/ExternalVaultFilesystem.ts";
 import { S3Bucket } from "./StorageAccessor/S3Bucket.ts";
 import type { StorageAccessor } from "./StorageAccessor/StorageAccessor.ts";
-export const decryptCompatOpenSSL = OpenSSLCompat.CBC.decryptCBC;
-export const encryptCompatOpenSSL = OpenSSLCompat.CBC.encryptCBC;
+import {
+    StorageAccessorTypes,
+    type StorageAccessorType,
+} from "./StorageAccessor/storage-accessor-types.ts";
 
-export enum FileType {
-    "Missing",
-    "File",
-    "Folder",
-}
-
-export type FsAPI = {
-    mkdir: typeof promises.mkdir;
-    writeFile: typeof promises.writeFile;
-    readFile: typeof promises.readFile;
-    stat: typeof promises.stat;
-    rm: typeof promises.rm;
-};
-
-export const StorageAccessorTypes = {
-    NORMAL: "normal",
-    DIRECT: "direct",
-    EXTERNAL: "external",
-    S3: "s3",
-} as const;
-
-export type StorageAccessorType = typeof StorageAccessorTypes[keyof typeof StorageAccessorTypes];
+export {
+    FileType,
+    StorageAccessorTypes,
+    type StorageAccessorType,
+} from "./StorageAccessor/storage-accessor-types.ts";
 
 export function getStorageTypeForBackupAccess(plugin: DiffZipBackupPlugin): StorageAccessorType {
     if (plugin.isDesktopMode) {