# TDD Wave 10: Data Integrity & Validation
**Status**: ✅ Complete
**Date**: 2026-02-19
**Focus**: Checksum verification and corruption detection
---
## Overview
Wave 10 adds data integrity features to the checkpointing system. Each checkpoint now includes a SHA-256 checksum computed over its data, enabling:
- Detection of data corruption
- Validation on restore/import
- Health checks with integrity verification
---
## Test Results
| 78 | Checkpoints include checksum on creation | ✅ |
| 79 | Checksum computation is correct | ✅ |
| 80 | Different data produces different checksum | ✅ |
| 81 | Validate returns true for valid checkpoint | ✅ |
| 82 | Service validate_checkpoint method works | ✅ |
| 83 | Export includes checksums | ✅ |
| 84 | Import handles checksums | ✅ |
| 85 | Health check validates recent checkpoints | ✅ |
| 86 | Batch validation of all checkpoints | ✅ |
| 87 | Validation report provides details | ✅ |
| 88 | Concurrent validation is safe | ✅ |
| 89 | Checksum algorithm is SHA-256 | ✅ |
| 90 | Validation catches tampered data | ✅ |
**Results**: 13 passed, 0 failed
---
## Implementation Details
### Checksum Field
Added `checksum` field to `TemporalCheckpoint`:
```rust
#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct TemporalCheckpoint {
// ... other fields ...
/// SHA-256 checksum for data integrity verification
pub checksum: String,
}
```
### Checksum Computation
Uses SHA-256 hash of serialized checkpoint data (excluding checksum itself):
```rust
impl TemporalCheckpoint {
pub fn new(...) -> Self {
let mut checkpoint = Self {
// ... init fields ...
checksum: String::new(),
};
checkpoint.checksum = checkpoint.compute_checksum();
checkpoint
}
fn compute_checksum(&self) -> String {
let data_for_hash = CheckpointDataForHash {
// All fields except checksum
id: self.id,
timestamp: self.timestamp,
// ... etc
};
let json = serde_json::to_vec(&data_for_hash).unwrap_or_default();
compute_checksum(&json) // SHA-256
}
}
```
### Validation
```rust
impl TemporalCheckpoint {
pub fn validate(&self) -> Result<()> {
let expected = self.compute_checksum();
if self.checksum != expected {
return Err(ReasoningError::ValidationFailed(
format!("Checksum mismatch: expected {}, got {}", expected, self.checksum)
));
}
Ok(())
}
}
```
---
## API Additions
### CheckpointService
| `validate_checkpoint(id)` | Validate a single checkpoint's checksum |
| `health_check_with_validation()` | Health check + validate recent checkpoints |
| `validate_all_checkpoints()` | Full validation of all checkpoints |
### ValidationReport
```rust
pub struct ValidationReport {
pub valid: usize, // Number of valid checkpoints
pub invalid: usize, // Number of invalid (corrupted) checkpoints
pub skipped: usize, // Legacy checkpoints without checksums
pub checked_at: Option<DateTime<Utc>>,
}
impl ValidationReport {
pub fn total(&self) -> usize { self.valid + self.invalid + self.skipped }
pub fn all_valid(&self) -> bool { self.invalid == 0 }
}
```
---
## Storage Format
Checkpoints stored in SQLiteGraph include the checksum:
```json
{
"id": "uuid",
"timestamp": "2026-02-19T12:34:56Z",
"sequence_number": 42,
"message": "...",
"tags": [],
"trigger": "manual",
"session_id": "uuid",
"state_data": "{...}",
"checksum": "a1b2c3d4..." // 64 hex chars (SHA-256)
}
```
---
## Backward Compatibility
- **Legacy checkpoints** (without checksum) are treated as valid
- Empty checksum field skips validation
- Storage layer handles missing checksum field gracefully
---
## Usage Examples
### Validate a Checkpoint
```rust
let service = CheckpointService::new(storage);
let id = service.checkpoint(&session, "Important state")?;
// Later, validate it
if service.validate_checkpoint(&id)? {
println!("Checkpoint is valid!");
} else {
println!("Checkpoint is corrupted!");
}
```
### Health Check with Validation
```rust
let health = service.health_check_with_validation()?;
if health.healthy {
println!("Service healthy: {}", health.message);
} else {
eprintln!("Data corruption detected: {}", health.message);
}
```
### Batch Validation
```rust
let report = service.validate_all_checkpoints()?;
println!("Validated {} checkpoints", report.total());
println!(" Valid: {}", report.valid);
println!(" Invalid: {}", report.invalid);
println!(" Skipped (legacy): {}", report.skipped);
if !report.all_valid() {
eprintln!("WARNING: Data corruption detected!");
}
```
---
## Security Considerations
- **SHA-256**: Industry-standard cryptographic hash
- **Not for security**: Checksums detect accidental corruption, not malicious tampering
- **No signature**: For malicious protection, add digital signatures
---
## Performance
| Create checkpoint | +~1μs (SHA-256 of ~1KB) |
| Validate checkpoint | ~1μs |
| Health check validation | O(sessions × 5) |
| Full validation | O(total checkpoints) |
---
## Files Modified
| `Cargo.toml` | Added `sha2` dependency |
| `src/checkpoint.rs` | Added checksum field, compute_checksum, validate |
| `src/errors.rs` | Added `ValidationFailed` error variant |
| `src/storage_sqlitegraph.rs` | Store/retrieve checksum |
| `src/service.rs` | Validation methods, ValidationReport |
| `src/lib.rs` | Export ValidationReport |
| `tests/data_integrity_tests.rs` | New test file (13 tests) |
---
## Future Enhancements
1. **Digital signatures**: Cryptographic signing for tamper-proofing
2. **Incremental validation**: Background validation of older checkpoints
3. **Repair mechanism**: Attempt to repair corrupted checkpoints from backups
4. **Checksum algorithms**: Configurable (BLAKE3, SHA3-256)
---
**Wave 10 Complete** ✅
Data integrity features ensure checkpoint reliability and provide tools for detecting corruption in production deployments.