`gh stack submit` does not save PR descriptions and titles if it fails

When `gh stack submit` fails (like due to a poor internet connection, GitHub downtime, or a git hook #346), it forgets all the edits made on the PR screen, and the user has to redo everything next time.

Start at the gh stack submit command and reproduce a failed submission, such as with a poor connection, GitHub downtime, or the git hook from issue #346. Trace how edits made on the PR screen are handled when submission fails. Done means titles and descriptions remain available on the next attempt instead of needing to be re-entered.

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