1.73.3

• a3eab04: Fix solve aborting with GitHub compare API not ready - cannot create PR safely when the compare/diff endpoint returns a transient HTTP 500 (this diff is temporarily unavailable due to heavy server load, code not_available). The auto-PR readiness gate polled /repos/{owner}/{repo}/compare/{base}...{head} to confirm the pushed commits were visible, but GitHub renders that diff lazily and returns 500 under load even though the branch and commits were already pushed and gh pr create (which does not render the full diff) would have succeeded. A new isTransientCompareApiError detector recognises the "heavy server load" / not_available 500 and the standard 5xx gateway codes (but NOT 404 fork mismatch or a literal 0), and the gate now degrades gracefully — marking the compare ready and proceeding to PR creation, still guarded by branch verification and the local git rev-list commit check. The fork-404 mismatch and genuine 0-commits paths remain fatal.

Related Pull Request: #1831

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