# Task 2: Add Encryption Error Handling — Final Summary

## Status: ✅ COMPLETE

### Deliverables Checklist
- [x] decrypt() function has try-catch around decipher.final() call
- [x] Error logged with context (not just message)
- [x] Returns ciphertext unchanged on error (no crash)
- [x] Test case verifies decrypt with invalid auth tag doesn't crash
- [x] Evidence saved to `.sisyphus/evidence/task-2-decrypt-error.txt`
- [x] Findings appended to `.sisyphus/notepads/fix-skills-memory-encryption/learnings.md`

### Implementation Summary

**File Modified:** `src/lib/db/encryption.ts` (lines 125-148)

**Key Changes:**
1. Added nested try-catch specifically around `decipher.final()` (line 132-142)
2. Enhanced error logging with context:
   - Error message from decipher.final()
   - Ciphertext prefix (first 30 chars) for debugging
   - Explanation about auth tag validation
3. Maintained outer catch for other decryption errors
4. Passthrough behavior: returns ciphertext unchanged on any error

**Error Handling Flow:**
```
decrypt(ciphertext)
  ├─ Check if encrypted (has prefix)
  ├─ Get encryption key
  ├─ Parse ciphertext format
  └─ Outer try-catch
      ├─ Create decipher
      ├─ Inner try-catch
      │   ├─ decipher.update()
      │   └─ decipher.final() ← Auth tag validation happens here
      │       └─ On error: log context + return ciphertext
      └─ On error: log + return ciphertext
```

### Test Results

All scenarios tested and verified:

| Scenario | Input | Result | Status |
|----------|-------|--------|--------|
| Invalid auth tag | `enc:v1:0000:0000:0000` | Returns unchanged | ✅ Pass |
| Malformed format | `enc:v1:invalid` | Returns unchanged | ✅ Pass |
| Non-encrypted | `plaintext-value` | Returns unchanged | ✅ Pass |
| Null input | `null` | Returns null | ✅ Pass |
| Undefined input | `undefined` | Returns undefined | ✅ Pass |

### Verification Results

- ✅ TypeScript diagnostics: No errors
- ✅ No crashes on invalid input
- ✅ Error logging includes full context
- ✅ Passthrough mode works correctly
- ✅ Backward compatible with existing code
- ✅ Consistent with encrypt() error handling pattern

### Evidence Files

1. `.sisyphus/evidence/task-2-decrypt-error.txt` — Detailed implementation report
2. `.sisyphus/evidence/task-2-summary.txt` — This file
3. `.sisyphus/notepads/fix-skills-memory-encryption/learnings.md` — Pattern documentation

### Next Steps

The decrypt() function is now production-ready with:
- Robust error handling that prevents crashes
- Detailed logging for debugging encrypted data issues
- Graceful degradation via passthrough mode
- Full backward compatibility

No further changes needed for this task.