fix: element tests drive the widget host protocol; the image element gets tests (WR-25)

The transfer element's busy and state=error handling is now tested
through the fake widget host, and golem15-seo-image gets tests for the
upload id matching, the error display, Remove and the disabled state.
The README's test gate runs npm test.

tests/elements/transfer.test.ts

@@ -1,6 +1,7 @@
 import { afterEach, beforeAll, describe, expect, it } from 'vitest'
 import { applyState, ROW_CAP, shownRows, type PreviewData, type PreviewRow } from '../../assets/src/elements/transfer'
 import { labelsFor } from '../../assets/src/elements/labels'
+import { HostFailure, mountWidget, settle } from './host'
 
 // E6 golem15-seo-transfer (UI-SPEC C13): Apply is enabled only after a
 // preview with no refused row and at least one change.
@@ -82,3 +83,50 @@ describe('E6 apply gating', () => {
     expect(node.querySelector('.seo-transfer__actions')).toBeNull()
   })
 })
+
+describe('E6 host protocol (WR-25)', () => {
+  function downloadButton(node: HTMLElement): HTMLButtonElement {
+    return node.querySelector<HTMLButtonElement>('.seo-transfer__section button')!
+  }
+
+  it('an export goes through the host and the buttons are busy until it settles', async () => {
+    const host = mountWidget('golem15-seo-transfer', {
+      attrs: { 'ui-locale': 'en', 'busy-label': 'Working…' },
+      answer: () => ({ op: 'export', filename: 'seo-redirects.csv', csv: 'source\n' }),
+    })
+    URL.createObjectURL = () => 'blob:x'
+    URL.revokeObjectURL = () => undefined
+    downloadButton(host.node).click()
+    expect(host.posted).toEqual([{ op: 'export', dataset: 'redirects' }])
+    expect(downloadButton(host.node).disabled).toBe(true)
+    expect(downloadButton(host.node).textContent).toBe('Working…')
+    downloadButton(host.node).click()
+    expect(host.emitted).toHaveLength(1)
+    await settle()
+    expect(downloadButton(host.node).disabled).toBe(false)
+  })
+
+  it('state=error unblocks the next request', async () => {
+    let fail = true
+    const host = mountWidget('golem15-seo-transfer', {
+      attrs: { 'ui-locale': 'en' },
+      answer: () => {
+        if (fail) {
+          fail = false
+          throw new HostFailure('export')
+        }
+        return { op: 'export', filename: 'seo-redirects.csv', csv: 'source\n' }
+      },
+    })
+    URL.createObjectURL = () => 'blob:x'
+    URL.revokeObjectURL = () => undefined
+    downloadButton(host.node).click()
+    await settle()
+    expect(host.node.getAttribute('state')).toBe('error')
+    expect(downloadButton(host.node).disabled).toBe(false)
+    downloadButton(host.node).click()
+    await settle()
+    expect(host.posted).toHaveLength(2)
+  })
+})
+