fix(prover-client): drop late stale-epoch reports + race-proof epoch teardown

[AztecBot]

Summary

Re-fix the flaky ProvingBroker > Retries > does not retry if job is stale (persisted variant) that caused PR #23344 to be dequeued from the merge queue (failing run, CI log key 64a972aafaa40dd0).

.test_patterns.yml previously suppressed this exact failure; #23260 removed the suppression after cleaning up in-memory state, but didn't address the underlying race between the broker's epoch cleanup and the LMDB-backed batched writes, so the flake recurred. The failure surfaces as Error('Store is closed') thrown out of BatchQueue.execProcessor → KVBrokerDatabase.commitWrites → SingleEpochDatabase.batchWrite → store.transactionAsync.

Fix

Two small, independent defenses:

1. proving_broker.ts — in both #reportProvingJobError and #reportProvingJobSuccess, after the existing !item early-return, also drop the report when this.isJobStale(item). A late report for a job whose epoch has been (or is being) cleaned up never reaches the database.
2. proving_broker_database/persisted.ts:
   • Track deletedEpochs: Set<number> so commitWrites short-circuits for epoch directories that are being torn down.
   • deleteAllProvingJobsOlderThanEpoch adds to deletedEpochs first, then removes from the epochs map before awaiting db.delete() (which synchronously marks the store closed and then awaits rm). This closes the window where a racing commitWrites could fetch a still-mapped, already-closed store.
   • Catch a residual Error('Store is closed') inside commitWrites as a benign drop. Any other error still propagates.

Verification

yarn workspace @aztec/prover-client test src/proving_broker/proving_broker.test.ts — 5 consecutive runs, 102/102 tests passing on each, including both in-memory and persisted variants of does not retry if job is stale.

Full analysis (failure timeline, the two races, why both defenses are needed): https://gist.github.com/AztecBot/612364332ec5a062bcf88ded9177334e

Test plan

• Persisted-variant does not retry if job is stale passes deterministically in CI under merge-queue-heavy concurrency
• No regressions in the rest of proving_broker.test.ts (retries, timeouts, database management blocks) — verified locally
• Merge-queue run on this PR completes cleanly

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Created by claudebox — group: slackbot

ClaudeBox log: https://claudebox.work/s/731f628c79243769?run=1