perf(jira): preserve replacement attachment download singleflight

src/main/jira/attachment-image-cache-generation.test.ts

@@ -0,0 +1,57 @@
+import { beforeEach, describe, expect, it } from 'vitest'
+import {
+  _resetAttachmentImageCache,
+  clearAttachmentImagesForSite,
+  getCachedAttachmentDataUrl,
+  loadAttachmentDataUrlWithCache
+} from './attachment-image-cache'
+
+type Image = { dataUrl: string; byteSize: number } | null
+function deferredImage() {
+  let resolve!: (image: Image) => void
+  let reject!: (error: Error) => void
+  const promise = new Promise<Image>((done, fail) => {
+    resolve = done
+    reject = fail
+  })
+  return { promise, resolve, reject }
+}
+
+beforeEach(_resetAttachmentImageCache)
+
+describe.each(['site', 'all'] as const)('attachment download after clearing %s', (scope) => {
+  it.each(['success', 'empty', 'failure'] as const)(
+    'keeps the replacement singleflight when the old download completes with %s',
+    async (outcome) => {
+      const old = deferredImage()
+      const replacement = deferredImage()
+      let downloads = 0
+      const load = () => {
+        downloads += 1
+        return downloads === 1 ? old.promise : replacement.promise
+      }
+      const args = { siteId: 'site-a', attachmentId: 'image-1', load }
+      const first = loadAttachmentDataUrlWithCache(args).catch(() => 'old failure')
+      clearAttachmentImagesForSite(scope === 'site' ? 'site-a' : undefined)
+      const second = loadAttachmentDataUrlWithCache(args)
+      expect(downloads).toBe(2)
+
+      if (outcome === 'failure') {
+        old.reject(new Error('old failure'))
+      } else {
+        old.resolve(outcome === 'empty' ? null : { dataUrl: 'old image', byteSize: 3 })
+      }
+      expect(await first).toBe(
+        outcome === 'failure' ? 'old failure' : outcome === 'empty' ? null : 'old image'
+      )
+      expect(getCachedAttachmentDataUrl('site-a', 'image-1')).toBeNull()
+
+      const third = loadAttachmentDataUrlWithCache(args)
+      expect(downloads).toBe(2)
+      replacement.resolve({ dataUrl: 'new image', byteSize: 3 })
+      expect(await second).toBe('new image')
+      expect(await third).toBe('new image')
+      expect(getCachedAttachmentDataUrl('site-a', 'image-1')).toBe('new image')
+    }
+  )
+})

src/main/jira/attachment-image-cache.ts

@@ -133,7 +133,10 @@ export async function loadAttachmentDataUrlWithCache(args: {
       }
       return loaded.dataUrl
     } finally {
-      inFlight.delete(key)
+      // A cleared generation no longer owns the current download's singleflight slot.
+      if (currentEpoch(args.siteId) === epochAtStart) {
+        inFlight.delete(key)
+      }
     }
   })()