When issue create or comment exits 6 (unreachable), the write may still have landed, so a retry can post twice. pr create already looks for an existing pull first.
Proposal: before writing, read the repo's knot for a ticket or comment by this author with the same title or body from the last few minutes. If one is found, report it (found: true, with its number or URI) instead of writing. --new forces a write. No stored state is needed.
Needs a decision: this adds a found field to --json.
Resolved by #1458, now merged.