Retry auto-merge enablement in the approval workflow.

[vorporeal]

Description

The approve workflow's auto-merge enable step (gh pr merge --auto --squash) occasionally fails with the GraphQL error Base branch was modified. Review and try the merge again. when the base branch is updated concurrently with our request — typically when another sync PR in the queue merges at the same moment. The previous code silently swallowed all failures via check=False, leaving the PR approved but without auto-merge enabled, which can stall the queue until some later event re-triggers the workflow.

This change wraps the auto-merge enablement in a retry loop: on stderr containing Base branch was modified, sleep 10s and retry, up to 3 attempts total. Non-retryable failures still fall through after a single attempt with a warning log, matching the prior behavior.

Example failure: https://github.com/warpdotdev/warp-internal/actions/runs/25027455954/job/73301658617

Testing

New unit tests in tests/workflows/test_approve_logic.py cover:

• success on the first attempt (no retries, no sleeps)
• retry-then-succeed when the first attempt hits the transient error
• give up after max_attempts without raising (so the escalation workflow can recover later)
• no retry for unrelated errors

Existing test suite still passes.

Co-Authored-By: Oz oz-agent@warp.dev

[vorporeal]

• Retry auto-merge enablement in the approval workflow. #35 👈 (View in Graphite)
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