# SQ-023: Node Recovery / Catch-Up

**Status:** `[ ] TODO`
**Blocked by:** SQ-021, SQ-018
**Priority:** Medium

## Description

A node that was offline catches up from peers or S3 when it rejoins.

## Files to Create/Modify

- `crates/sq-cluster/src/recovery.rs` - on-join catch-up logic
- `crates/sq-server/src/grpc/cluster.rs` - FetchSegment RPC impl
- `crates/sq-cluster/src/replication.rs` - integrate recovery into join flow

## Recovery Flow

1. Rejoining node contacts peers via seed list
2. For each topic-partition, compare local latest offset with peers
3. If peer has newer data: fetch missing segments via FetchSegment RPC
4. If peer has also trimmed: fetch from S3
5. Replay fetched segments into local WAL
6. Mark node as "caught up" and start accepting writes

## Acceptance Criteria

- [ ] Node joins late: fetches missing data from peer, all messages readable
- [ ] Node catches up from S3 when peer has trimmed that segment
- [ ] Recovery doesn't block existing cluster operations
- [ ] Recovery progress is logged