# SQ-016: Object Store Shipping

**Status:** `[x] DONE`
**Blocked by:** SQ-007
**Priority:** Medium

## Description

Background process that ships closed WAL segments to S3-compatible object storage for long-term durability.

## Files to Create/Modify

- `crates/sq-storage/src/object_store/mod.rs` - ObjectStore trait + S3 impl + Noop impl
- `crates/sq-storage/src/object_store/shipper.rs` - SegmentShipper as notmad::Component
- `crates/sq-storage/src/object_store/layout.rs` - S3 key naming convention

## ObjectStore Trait

```rust
pub trait ObjectStore: Send + Sync {
    async fn put(&self, key: &str, data: Vec<u8>) -> Result<()>;
    async fn get(&self, key: &str) -> Result<Vec<u8>>;
    async fn list(&self, prefix: &str) -> Result<Vec<String>>;
    async fn delete(&self, key: &str) -> Result<()>;
}
```

## S3 Key Layout

`{cluster_id}/{topic}/{partition}/{base_offset}-{end_offset}.sqseg`

## Acceptance Criteria

- [ ] Closed segment is detected and uploaded to object store
- [ ] S3 key matches expected layout
- [ ] Noop object store works for testing (stores in memory)
- [ ] Upload failure: segment stays local, retried on next cycle
- [ ] Successful upload is recorded (segment marked as "shipped")
- [ ] Uses zstd compression before upload

## Notes

- Uses `object_store` crate with AWS S3 features (same as nostore)
- Shipper runs as a notmad::Component in the background
- Poll interval: every 5 seconds check for closed segments