# TDD Wave 1: Core Checkpointing
**Status**: ✅ Complete
**Date**: 2026-02-19
**Focus**: Basic checkpoint creation and identification
---
## Overview
Wave 1 establishes the foundation of the temporal checkpointing system. The goal is to implement basic checkpoint creation with unique identifiers and sequence numbers.
---
## Test Results
| 1 | Create in-memory storage | ✅ |
| 2 | Create checkpoint manager | ✅ |
| 3 | Create a checkpoint | ✅ |
| 4 | Checkpoint IDs are unique | ✅ |
| 5 | Sequence numbers increment | ✅ |
| 6 | List checkpoints (empty) | ✅ |
| 7 | Auto-checkpoint throttling | ✅ |
| 8 | Manual checkpoint (no throttle) | ✅ |
| 9 | Session ID attached | ✅ |
| 10 | Environment info captured | ✅ |
**Results**: 10 passed, 0 failed
---
## Implementation
### Core Types Added
```rust
/// Unique identifier for a checkpoint
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct CheckpointId(pub Uuid);
/// Unique identifier for a debugging session
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct SessionId(pub Uuid);
/// A snapshot of debugging state
pub struct TemporalCheckpoint {
pub id: CheckpointId,
pub timestamp: DateTime<Utc>,
pub sequence_number: u64,
pub message: String,
pub tags: Vec<String>,
pub state: DebugStateSnapshot,
pub trigger: CheckpointTrigger,
pub session_id: SessionId,
}
```
### Storage Trait
```rust
pub trait CheckpointStorage: Send + Sync {
fn store(&self, checkpoint: &TemporalCheckpoint) -> Result<()>;
fn get(&self, id: CheckpointId) -> Result<TemporalCheckpoint>;
fn list_by_session(&self, session_id: SessionId) -> Result<Vec<CheckpointSummary>>;
}
```
### Key Features
1. **UUID-based IDs**: Each checkpoint gets a unique v4 UUID
2. **Per-manager sequences**: Each manager maintains its own counter
3. **Throttling**: Auto-checkpoints are throttled (30-second default)
4. **Manual override**: User-initiated checkpoints bypass throttling
---
## Design Decisions
### 1. UUID vs Sequential IDs
**Chosen**: UUID v4 for checkpoint IDs
**Rationale**:
- Globally unique without coordination
- No central ID server needed
- Secure (not guessable)
### 2. In-Memory vs Persistent Storage
**Chosen**: Both supported via trait
**Rationale**:
- In-memory for testing
- SQLiteGraph for production
- Easy to add new backends
### 3. Throttling Strategy
**Chosen**: Time-based (30 seconds)
**Rationale**:
- Prevents checkpoint spam
- Simple to understand
- Configurable per-manager
---
## Code Metrics
| `src/checkpoint.rs` | ~200 |
| `src/storage.rs` | ~60 |
| `src/errors.rs` | ~40 |
| `tests/checkpoint_tests.rs` | ~200 |
---
## Next Steps
Wave 2 will add query methods (get, list, restore) to make checkpoints useful.
---
**Wave 1 Complete** ✅
Foundation established with core checkpoint creation and storage abstraction.