PR: https://git.cafe/pingdotgg/t3code/pulls/25428
GitHub: https://github.com/pingdotgg/t3code/pull/25428
main: 32ecd71726fee16f335484c1f95cbce126d461f6
PR head: 3dabba59bfb8327bd95c972d4857f5eb872aff68
Linux Boat VM, actual desktop client and real Codex gpt-6.1-sol turns.
Playwright from repository dependencies; Chrome web UI used /usr/bin/google-chrome.
Desktop UI automation used connectOverCDP with noDefaults:true to avoid changing app downloads.

MAIN REPRODUCTION
Started vp run dev in ../main; then used dev:web plus the actual Electron client and its local backend.
Local desktop state: /tmp/t3-main-desktop
Agent opened a fresh native preview and downloaded the real repository report.
Preview navigator.userAgent contained Electron/44.10.0, not HeadlessChrome.
Settings > Appearance > Export Download isolation:
  no native save dialog opened
  theme appeared at /tmp/playwright-artifacts-j4Kawm/f89dc494-2243-40a6-8ccf-1434dd36fe43
  file size: 3367 bytes
  parsed theme name: Download isolation

EXACT PR HEAD
vp i completed; vp run dev booted, followed by dev:web and the actual Electron client with its local backend.
Final local desktop state: /tmp/t3-pr-desktop
Provider: Codex gpt-6.1-sol, real turns through the composer.
Preview navigator.userAgent:
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) T3CodeDev/0.0 Chrome/152.0.7977.167 Electron/44.9.3 Safari/537.36
Settings > Appearance > Export Download isolation with the native preview attached:
  native save dialog opened
  selected Downloads, clicked Save
  /home/user/Downloads/download-isolation.json: 3367 bytes
Repeated with Desktop selected:
  /home/user/Desktop/download-isolation.json: 3367 bytes
cmp /tmp/main-diverted-theme.json /home/user/Downloads/download-isolation.json
  exit 0, no output
cmp /tmp/main-diverted-theme.json /home/user/Desktop/download-isolation.json
  exit 0, no output
SHA256 of all three theme exports:
8e010bec0392b2bb1d9d9210a16a8d3cfb2706e4a81c0a87c343d626f6791080

NEIGHBORING BEHAVIOR
Export > Cancel: saved file size and modification time unchanged, no diverted export file.
Native preview report download before and after theme export and cancellation:
  277 bytes, timeout 10 cmp <downloaded-file> repo-report.txt: exit 0, no output.
Separate Chrome web client, real Codex turn: 277-byte report download also matched exactly.

EXISTING CHECKS THROUGH BLACKSMITH
vp i
vp test run apps/desktop/src/preview/CdpRelay.test.ts apps/desktop/src/preview/DesktopBrowserHost.test.ts
  CdpRelay.test.ts: 11 passed
  DesktopBrowserHost.test.ts: 32 passed
  2 files, 43 tests passed
PR reported 7 successful checks, 0 failing, 0 pending at verification time.

NOT EXERCISED
macOS and Windows native save dialogs; native iOS and Android clients.
Preview denial/reallow and rejected-command state preservation were covered by the existing tests, not a separate interactive runtime check.
Paired light/dark theme export was not separately exercised; runtime export used a custom single-appearance theme.
No source changes or pushes were needed. No merge, close, rebase, force-push, or label changes.