Revisit AWS Backup retention for old EFS-era volume (daily 600GB snapshots)

## Revisit AWS Backup retention for the old EFS-era volume

The account (us-east-1) has an AWS Backup plan taking **daily 600 GB snapshots**, with ~15 currently retained (~8.8 TB provisioned; snapshots are incremental so the real stored/billed size is much lower).

These are **intentional** — at least one lineage is the old EFS drive from the wholesale switch to cefs. That migration has been stable for months now, so it's worth revisiting:

- Do we still need daily cadence, or would weekly + longer tail suffice?
- Can the retention window shrink (or the plan be retired entirely) now that cefs is proven?
- Confirm exactly which volume(s) the plan covers and whether anything else depends on it.

Sample recent snapshots: `snap-075ec8caf09650372` (2026-07-09), `snap-0144cd9a56ed36d3c` (2026-07-08), … daily series.

No urgency — surfaced during the 2026-07-10 AMI audit (#2220) but deliberately kept separate from that cleanup.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Start by locating the AWS Backup plan covering the old EFS-era volume in us-east-1 and compare it with snapshots such as snap-075ec8caf09650372 and snap-0144cd9a56ed36d3c. Confirm which volumes and dependencies are covered, then determine whether daily retention should be reduced, changed to weekly with a longer tail, or retired. Done means the dependency and retention decision are documented and the backup configuration reflects it.

Written by the indexing model from the issue text.