fix: protect download bytes and recover local API errors

src/utils/downloadUtils.test.ts

@@ -0,0 +1,26 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+import { saveData } from './downloadUtils'
+
+vi.mock('./tauri', () => ({ isTauri: () => false }))
+
+describe('browser file downloads', () => {
+  beforeEach(() => {
+    vi.spyOn(HTMLAnchorElement.prototype, 'click').mockImplementation(() => {})
+    vi.stubGlobal('URL', { createObjectURL: vi.fn(() => 'blob:test'), revokeObjectURL: vi.fn() })
+  })
+
+  it('downloads exactly the requested byte view without surrounding buffer contents', async () => {
+    const bytes = new Uint8Array([11, 22, 33, 44, 55])
+    saveData(bytes.subarray(1, 4), 'slice.bin')
+
+    const blob = vi.mocked(URL.createObjectURL).mock.calls[0][0] as Blob
+    const contents = await new Promise<ArrayBuffer>((resolve, reject) => {
+      const reader = new FileReader()
+      reader.onload = () => resolve(reader.result as ArrayBuffer)
+      reader.onerror = reject
+      reader.readAsArrayBuffer(blob)
+    })
+    expect([...new Uint8Array(contents)]).toEqual([22, 33, 44])
+    expect(blob.type).toBe('application/octet-stream')
+  })
+})