Billing→S3: end-to-end test + reconciliation

[Hazel-Datastax]

Full-path verification and a reconciliation check.

What to do

• End-to-end IT (LocalStack): enabled=true, run a vectorize/rerank flow, assert .jsonl objects land at the expected keys, lines match the logger output, and ids are unique.
• Reconciliation utility: compare logger-emitted lines vs S3-delivered events (quantify any gap). Once the real dev bucket is reachable, verify events appear in BigQuery.

Acceptance

• E2E IT passes against LocalStack.
• Reconciliation reports zero gap in the test.