[fix] Transactional reads for metadata update and delete

[St4NNi]

Goal

Metadata update and delete read registry state and derive events before their write transaction starts, so concurrent delete/update interleavings can resurrect deleted state or record stale tombstone fences.

Workplan

1. Re-read and validate registry state inside the write transaction
2. Compare expected last-event id/revision; retry on mismatch or conflict
3. Cover both operations with deterministic interleaving tests

Definition of Done

• Update-after-delete and delete-after-update interleavings produce no resurrection or stale fence
• Conflicts surface as retries, not corruption

Test Concept

Barrier-forced interleavings in operation tests.

Risks

Coordinate with the current placement-branch fix run, which touches the same files.