fix(session-export): preserve streamed browser downloads

apps/web/tests/navigation-panes.e2e.ts

@@ -52,6 +52,11 @@ async function assertBaselineSucceeded(response: Response, method: string): Prom
 }
 
 async function ensureSeedOpen(page: Page): Promise<void> {
+  const welcome = page.locator('[class*="onboardingOverlay"]')
+  if (await welcome.count() > 0) {
+    await welcome.getByRole('button').click()
+    await welcome.waitFor({ state: 'detached', timeout: 15_000 })
+  }
   const chat = page.getByRole('tab', { name: 'Chat', exact: true })
   // Search is a collapsed header action; expand it so the input is actionable.
   const searchButton = page.getByRole('button', { name: 'Search sessions' })
@@ -297,7 +302,8 @@ describe('web e2e: navigation & panes over a rich seeded session', () => {
     }
     expect(headerBox.x + headerBox.width - (buttonBox.x + buttonBox.width)).toBeLessThanOrEqual(32)
     const responsePromise = page.waitForResponse(response =>
-      new URL(response.url()).pathname === '/api/session.export', { timeout: 30_000 })
+      response.request().method() === 'HEAD'
+      && new URL(response.url()).pathname === '/api/session.export', { timeout: 30_000 })
     const downloadPromise = page.waitForEvent('download', { timeout: 30_000 })
     await exportButton.click()
     const response = await responsePromise
@@ -315,17 +321,61 @@ describe('web e2e: navigation & panes over a rich seeded session', () => {
     expect(content).toContain('FIRST_DONE')
     await dialog.getByText('Close', { exact: true }).click()
 
-    const input = page.locator('textarea').first()
-    const slashDownloadPromise = page.waitForEvent('download', { timeout: 30_000 })
-    await input.fill('/export')
-    await page.getByRole('option', { name: /export/u }).waitFor({ timeout: 10_000 })
-    await input.press('Enter')
-    const slashDownload = await slashDownloadPromise
-    expect(slashDownload.suggestedFilename()).toBe(download.suggestedFilename())
-    await page.getByRole('dialog', { name: 'Session download started' }).waitFor({ timeout: 30_000 })
-    await page.getByRole('dialog', { name: 'Session download started' })
-      .getByText('Close', { exact: true }).click()
-  }, 60_000)
+    const observer = await newEnglishPage(browser)
+    const observerTripwire = watchConsole(observer)
+    const observerSlotErrors: string[] = []
+    let observerDownloads = 0
+    observer.on('download', () => { observerDownloads += 1 })
+    observer.on('console', (message) => {
+      if (message.type() === 'error' && /slot entry crashed/i.test(message.text())) {
+        observerSlotErrors.push(message.text())
+      }
+    })
+    const observerSessionBaseline = baselineResponse(observer, 'session.list')
+    const observerWorkspaceBaseline = baselineResponse(observer, 'workspace.list')
+    const [, observerSessionResponse, observerWorkspaceResponse] = await Promise.all([
+      observer.goto(scaffold.baseUrl, { waitUntil: 'load' }),
+      observerSessionBaseline,
+      observerWorkspaceBaseline,
+    ])
+    await Promise.all([
+      assertBaselineSucceeded(observerSessionResponse, 'observer session.list'),
+      assertBaselineSucceeded(observerWorkspaceResponse, 'observer workspace.list'),
+    ])
+    await observer.getByText('Ungrouped', { exact: true }).waitFor({ timeout: 30_000 })
+    await ensureSeedOpen(observer)
+
+    try {
+      const input = page.locator('textarea').first()
+      const slashDownloadPromise = page.waitForEvent('download', { timeout: 30_000 })
+      await input.fill('/export')
+      await page.getByRole('option', { name: /export/u }).waitFor({ timeout: 10_000 })
+      await input.press('Enter')
+      const slashDownload = await slashDownloadPromise
+      expect(slashDownload.suggestedFilename()).toBe(download.suggestedFilename())
+      const slashFiles = unzipSync(await readFile(await slashDownload.path()))
+      const slashContent = strFromU8(slashFiles['session.jsonl'] as Uint8Array)
+      const slashEvents = parseSessionLog(slashContent)
+      const exportRun = slashEvents.findLast(event => event.type === 'command/run' && event.data.name === 'export')
+      if (exportRun?.type !== 'command/run') throw new Error('slash ZIP has no export command/run')
+      const exportDone = slashEvents.find(event =>
+        event.type === 'command/done' && event.data.commandId === exportRun.data.commandId)
+      expect(exportDone?.type).toBe('command/done')
+      await page.getByRole('dialog', { name: 'Session download started' }).waitFor({ timeout: 30_000 })
+      await page.getByRole('dialog', { name: 'Session download started' })
+        .getByText('Close', { exact: true }).click()
+      await observer.getByText('Session log download requested.', { exact: true }).waitFor({ timeout: 30_000 })
+      expect(observerDownloads).toBe(0)
+      expect(await observer.getByRole('dialog', { name: 'Session download started' }).count()).toBe(0)
+      expect({
+        pageErrors: observerTripwire.pageErrors,
+        slotErrors: observerSlotErrors,
+        warnings: observerTripwire.warnings,
+      }).toEqual({ pageErrors: [], slotErrors: [], warnings: [] })
+    } finally {
+      await observer.close()
+    }
+  }, 120_000)
 
   it.skipIf(MODE === 'record')('focuses the ledger by dragging an overview interval', async () => {
     onTestFailed(() => saveFailureShot(page, 'web-e2e-navigation-timeline'))