Update-check failure (offline / unreachable manifest) shows as a red error banner on every step

[fkb032]

@farhankhalaf said:

fyi haven't seen this error before

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What the screenshot shows (decoded 2026-08-27)

Banner text: "Update check failed: [updater] check failed: error sending request for url (https://releases.nixm…" — the Tauri updater couldn't reach releases.nixmac.com (DNS/offline/transient), and the app rendered that as a full-width red error banner at the top of the step area. The banner is mounted globally in widget.tsx ~L288, between the Stepper and the step content, so it shows on every step — the screenshot just happened to be on Describe. Nothing in the app was actually broken.

Where

• hooks/use-updater.ts ~L81: the check error is console.error'd and stored as banner error state (errorSource: "check").
• components/widget/layout/update-banner.tsx ~L62-68 renders Update check failed: {error} in the same red banner used for install failures.
• The check runs once per launch from the mount effect (use-updater.ts ~L159-191, guarded by checkedRef); it is skipped when a developer version pin is active, in dev builds (Rust stub at commands/updater.rs ~L99-103 — so this can't be reproduced under devenv up), and with NIXMAC_DISABLE_UPDATER=1. Changing the update channel does not re-check until the next launch. So every release-build user who launches offline sees this.

Acceptance criteria

• [Decision] The automatic launch-time update check failing (network error, non-2xx, malformed manifest) does not show the red banner. It is console.warn'd with the underlying error and emits a new update_check_failed telemetry event — add the variant to the TelemetryEvent union in lib/telemetry/types.ts ~L68-70; props = a short reason code, not the raw string (it contains the manifest URL). Remove the now-dead errorSource: "check" branch (use-updater.ts ~L23, update-banner.tsx ~L67). There is no manual check trigger today, so silent-on-failure is safe; if one is added later it must surface the failure inline.
• A failed update install keeps the current banner behavior (errorSource: "install").
• Follow-up (separate ticket, not in this estimate): a user-visible "Couldn't check for updates" line + manual Check again action. There is no Updates settings tab today (update UI lives only in Developer → Update channel, dev-mode-gated), no manual check trigger, and updater state is per-hook-instance — so this needs a shared store + new UI.
• Unit test on the hook (renderHook + vi.mock, as in use-rollback.test.ts): check rejection → no banner error state; install rejection → banner error state. Run with import.meta.env.DEV stubbed false (vi.stubEnv) — the hook's dev-mode guards at ~L66 / ~L110 otherwise swallow both errors and the test proves nothing.

~1–2h for the required ACs (frontend only; use-updater.ts / update-banner.tsx are Cooper's). Verify only in a release build — dev stubs the updater. Not a bug in the updater itself; releases.nixmac.com resolves today.

[linear-code]

ENG-620