Handle document-read errors (e.g., Google Docs authorization timeout)

[kcarnold]

The change on Draft may not be correct:

One real bug — draft's Retry re-runs the wrong request. frontend/src/pages/draft/index.tsx:454 sets the error via updateErrorInfo directly, outside getSuggestion, so lastRequestRef.current (set at :319) is never updated. For a non-auth ScriptError the notice is retryable: true, so a Retry button appears — and retryLastRequest (:377) re-runs whatever request last succeeded, with its stale docContext. Concretely: writer runs "Questions" on their intro, keeps writing for ten minutes, clicks a feature, the bridge hiccups, they hit Retry — and get a fresh-looking suggestion generated from the document as it was ten minutes ago. If there was no earlier request it silently does nothing. Revise gets this right (retryVisualization re-enters requestVisualization from the top, :503) and chat gets it right (Retry re-enters submitMessage, which redoes the read); draft is the odd one out. Cheapest fix is to have the catch stash the intended mode so Retry re-enters requestSuggestion(mode).

But maybe we just drop the retry functionality entirely; an error of any kind shouldn't end up in the history.