Distillation

🔴 (03:06) Added test "fetches stable releases only from the explicitly selected Toolkit source", recording requested URLs and validating that stable-release fetching uses the explicitly selected Toolkit source.
🔴 (03:06) Added coverage ensuring nightly transport error text is not misclassified as a not-found response; the operation must reject with UpgradeError.
🔴 (03:06) The update-check test "checks for update when never checked before" verifies that when getVersionCheckInfo().lastChecked is null, shouldCheckForUpdate returns true and initiates the background update check.
🔴 (03:06) Upgrade tests explicitly select the Toolkit source with const toolkitSource = UPGRADE_SOURCES[0]!.
🔴 (03:06) Nightly upgrade mocks return gzipped blob data directly with HTTP status 200 for URLs containing "/blobs/", without requiring a redirect; unmatched requests return "Not Found" with HTTP status 404.
🔴 (03:06) Installation-method detection remains covered by an assertion that detectInstallationMethod() returns "brew".

Observations