auto-format: push-race rebase conflict aborts the pass (run 41684257818) — make conflicted passes retryable/distinguishable

Finding (2026-11-04, from task 7586 revalidation of #4787)

Scheduled auto-format run 41684257818 (2026-11-03T17:26:26Z, head 4ab80c458) fired correctly but the pass failed at the push step:

The workflow's format commit (2b36e5430) raced a newer main; the push was rejected non-fast-forward.
The workflow's rebase retry hit a content conflict in pm-stack/aggregator/test/quota-current.test.ts (auto-merging pm-stack/aggregator/events.json, src/render.ts, and two test files) and aborted: error: could not apply 2b36e5430... style(treefmt): auto-format on main, exit 1.
Impact was self-healing this time: the next scheduled run (41730853769, 2026-11-03T22:26Z) succeeded and the pass at 23:12Z pushed b65342bc. But a conflicted pass silently drops that range's formatting until a later clean pass covers it, and the failure looks identical to a formatting failure in the run list.

On a rebase conflict during the auto-format push retry, the workflow either (a) drops the conflicted files from its format commit and pushes the remainder, (b) abandons its commit cleanly with a distinct, greppable log line (e.g. auto-format: push abandoned, range will be retried next pass) and a success/neutral exit for the record step, or (c) another mechanism that makes a push-race conflict distinguishable from a formatter failure and guarantees the range is retried.
A verification run or workflow-level test demonstrates the chosen behavior on a simulated conflicting push.

Related: #4787 (parent findings; closed with the schedule/token/biome findings resolved), #2014 (closed fleet-wide format tracker).