fix: return all SQS messages as batch failures on non-ScaleError exceptions; enable throttle retries

[Copilot]

Description

When scaleUp() throws any non-ScaleError exception (SSM ThrottlingException, EC2 Unavailable, GitHub API errors), scaleUpHandler returns an empty batchItemFailures array. SQS interprets this as "all messages processed successfully" and permanently deletes them. Jobs queue indefinitely with no runner assigned and no DLQ routing.

Root cause in lambda.ts: the else branch in the catch block never populates batchItemFailures:

// BEFORE — returns [] → SQS deletes all messages permanently
} else {
  logger.error(`...ignoring batch`, { error: e });
}

// AFTER — all messages returned as failures → SQS retries
} else {
  logger.error(`...batch will be retried via SQS.`, { error: e });
  batchItemFailures.push(...sqsMessages.map(({ messageId }) => ({ itemIdentifier: messageId })));
}

Contributing bug in auth.ts: onRateLimit and onSecondaryRateLimit handlers don't return true, so @octokit/plugin-throttling aborts immediately instead of retrying — the resulting exception then hits the empty batchItemFailures path above.

Changes:

• lambda.ts: Populate batchItemFailures with all message IDs in the non-ScaleError catch path
• auth.ts: Add return true to both throttle handlers to enable retry
• lambda.test.ts: Update tests to assert correct retry behavior; add empty-batch edge case

Test Plan

• Updated existing tests that were asserting the broken behavior (batchItemFailures: [] for non-ScaleError)
• Added edge case test for empty batch with non-ScaleError
• Full control-plane test suite passes (354 tests, 13 files)

Related Issues

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

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