# POST3-003: Repository layer and Store API

**Status:** Done
**Priority:** P0
**Blocked by:** POST3-002

## Description

Implement the repository layer (raw SQL CRUD for each table) and the high-level Store API that orchestrates them with transactions and chunking logic.

## Acceptance Criteria

- [ ] `repositories/buckets.rs` — create, get_by_name, list, delete, is_empty
- [ ] `repositories/objects.rs` — upsert, get, delete, list (with prefix + pagination)
- [ ] `repositories/blocks.rs` — insert_block, get_all_blocks (ordered by block_index)
- [ ] `repositories/metadata.rs` — insert_batch, get_all (for an object_id)
- [ ] `store.rs` — Store struct with all public methods:
  - create_bucket, head_bucket, delete_bucket, list_buckets
  - put_object (chunking + MD5 ETag + metadata, all in a transaction)
  - get_object (reassemble blocks + fetch metadata)
  - head_object, delete_object, list_objects_v2
  - get_object_metadata
- [ ] put_object correctly splits body into 1 MiB blocks
- [ ] get_object correctly reassembles blocks in order
- [ ] Overwriting an object deletes old blocks+metadata via CASCADE
- [ ] `cargo check -p post3` passes