Here's your `DEVELOPMENT.md`:

```markdown
# Development Guide - SeedPGP v1.1.0

## Architecture Quick Reference

### Core Types

```typescript
// src/lib/types.ts
interface SeedPgpPlaintext {
  v: number;              // Version (always 1)
  t: string;              // Type ("bip39")
  w: string;              // Mnemonic words (normalized)
  l: string;              // Language ("en")
  pp: number;             // BIP39 passphrase used? (0 or 1)
  fpr?: string[];         // Optional recipient fingerprints
}

interface ParsedSeedPgpFrame {
  kind: "single";         // Frame type
  crc16: string;          // 4-digit hex checksum
  b45: string;            // Base45 payload
}
```

### Frame Format

```
SEEDPGP1:0:ABCD:BASE45DATA

SEEDPGP1 - Protocol identifier + version
0        - Frame number (single frame)
ABCD     - CRC16-CCITT-FALSE checksum (4 hex digits)
BASE45   - Base45-encoded PGP binary message
```

### Key Functions

#### Encryption Flow
```typescript
buildPlaintext(mnemonic, bip39PassphraseUsed, recipientFingerprints?)
  → SeedPgpPlaintext

encryptToSeedPgp({ plaintext, publicKeyArmored?, messagePassword? })
  → { framed: string, pgpBytes: Uint8Array, recipientFingerprint?: string }
```

#### Decryption Flow
```typescript
decryptSeedPgp({ frameText, privateKeyArmored?, privateKeyPassphrase?, messagePassword? })
  → SeedPgpPlaintext

frameDecodeToPgpBytes(frameText)
  → Uint8Array (with CRC16 validation)
```

#### Encoding/Decoding
```typescript
frameEncode(pgpBinary: Uint8Array) → "SEEDPGP1:0:CRC16:BASE45"
frameParse(text: string) → ParsedSeedPgpFrame
frameDecodeToPgpBytes(frameText: string) → Uint8Array
```

### Dependencies

```json
{
  "openpgp": "^6.3.0",      // PGP encryption (curve25519Legacy)
  "bun-types": "latest",    // Bun runtime types
  "react": "^18.x",         // UI framework
  "vite": "^5.x"            // Build tool
}
```

### OpenPGP.js v6 Quirks

⚠️ **Important compatibility notes:**

1. **Empty password array bug**: Never pass `passwords: []` to `decrypt()`. Only include if non-empty:
   ```typescript
   if (msgPw) {
     decryptOptions.passwords = [msgPw];
   }
   ```

2. **Curve naming**: Use `curve25519Legacy` (not `curve25519`) in `generateKey()`

3. **Key validation**: Always call `getEncryptionKey()` to verify public key has usable subkeys

## Project Structure

```
seedpgp-web/
├── src/
│   ├── lib/
│   │   ├── seedpgp.ts        # Core encrypt/decrypt logic
│   │   ├── seedpgp.test.ts   # Test vectors (15 tests)
│   │   ├── base45.ts         # Base45 encoder/decoder
│   │   ├── crc16.ts          # CRC16-CCITT-FALSE
│   │   └── types.ts          # TypeScript interfaces
│   ├── App.tsx               # React UI entry
│   └── main.tsx              # Vite bootstrap
├── package.json
├── tsconfig.json
├── vite.config.ts
├── README.md
└── DEVELOPMENT.md            # This file
```

## Development Workflow

### Running Tests

```bash
# All tests
bun test

# Watch mode
bun test --watch

# Verbose output
bun test --verbose
```

### Development Server

```bash
bun run dev          # Start Vite dev server
bun run build        # Production build
bun run preview      # Preview production build
```

### Adding Features

1. **Write tests first** in `seedpgp.test.ts`
2. **Implement in** `src/lib/seedpgp.ts`
3. **Update types** in `types.ts` if needed
4. **Run full test suite**: `bun test`
5. **Commit with conventional commits**: `feat: add QR generation`

## Feature Agenda

### 🚧 v1.2.0 - QR Code Round-Trip

**Goal**: Read back QR code and decrypt with user-provided credentials

**Tasks**:
- [ ] Add QR code generation from `encrypted.framed`
  - Library: `qrcode` or `qr-code-styling`
  - Input: SEEDPGP1 frame string
  - Output: QR code image/canvas/SVG
  
- [ ] Add QR code scanner UI
  - Library: `html5-qrcode` or `jsqr`
  - Camera/file upload input
  - Parse scanned text → `frameText`
  
- [ ] Build decrypt UI form
  - Input fields:
    - Scanned QR text (auto-filled)
    - Private key (file upload or paste)
    - Key passphrase (password input)
    - OR message password (alternative)
  - Call `decryptSeedPgp()`
  - Display recovered mnemonic + metadata
  
- [ ] Add visual feedback
  - CRC16 validation status
  - Key fingerprint match indicator
  - Decryption success/error states

**API Usage**:
```typescript
// Generate QR
import QRCode from 'qrcode';
const { framed } = await encryptToSeedPgp({ ... });
const qrDataUrl = await QRCode.toDataURL(framed);

// Scan and decrypt
const scannedText = "SEEDPGP1:0:ABCD:..."; // from scanner
const decrypted = await decryptSeedPgp({
  frameText: scannedText,
  privateKeyArmored: userKey,
  privateKeyPassphrase: userPassword,
});
console.log(decrypted.w); // Recovered mnemonic
```

**Security Notes**:
- Never log decrypted mnemonics in production
- Clear sensitive data from memory after use
- Validate CRC16 before attempting decrypt
- Show key fingerprint for user verification

---

### 🔮 Future Ideas (v1.3+)

- [ ] Multi-frame support (for larger payloads)
- [ ] Password-only (SKESK) encryption flow
- [ ] Shamir Secret Sharing integration
- [ ] Hardware wallet key generation
- [ ] Mobile companion app (React Native)
- [ ] Printable paper backup templates
- [ ] Encrypted cloud backup with PBKDF2
- [ ] BIP85 child mnemonic derivation

## Debugging Tips

### Enable verbose PGP logging

Uncomment in `seedpgp.ts`:
```typescript
console.log("Raw PGP hex:", Array.from(pgpBytes).map(...));
console.log("SeedPGP: message packets:", ...);
console.log("SeedPGP: encryption key IDs:", ...);
```

### Test with known vectors

Use Trezor vectors from test file:
```bash
bun test "Trezor"  # Run only Trezor tests
```

### Validate frame manually

```typescript
import { frameParse } from "./lib/seedpgp";
const parsed = frameParse("SEEDPGP1:0:ABCD:...");
console.log(parsed); // Check structure
```

## Code Style

- **Functions**: Async by default, explicit return types
- **Errors**: Throw descriptive Error objects with context
- **Naming**: `camelCase` for functions, `PascalCase` for types
- **Comments**: Only for non-obvious crypto/encoding logic
- **Testing**: One test per edge case, descriptive names

## Git Workflow

```bash
# Feature branch
git checkout -b feat/qr-generation

# Conventional commits
git commit -m "feat(qr): add QR code generation"
git commit -m "test(qr): add QR round-trip test"

# Tag releases
git tag -a v1.2.0 -m "Release v1.2.0 - QR round-trip"
git push origin main --tags
```

## Questions for Next Session

When continuing development, provide:

1. **Feature context**: "Adding QR code generation for v1.2.0"
2. **Current code**: Paste relevant files you're modifying
3. **Specific question**: "How should I structure the QR scanner component?"

Example starter prompt:
```
I'm working on seedpgp-web v1.1.0 (BIP39 PGP encryption tool).

[Paste this DEVELOPMENT.md section]
[Paste relevant source files]

I want to add QR code generation. Here's my current seedpgp.ts...
```

---

**Last Updated**: 2026-01-28  
**Maintainer**: @kccleoc
```

Now commit it:

```bash
git add DEVELOPMENT.md
git commit -m "docs: add development guide with v1.2.0 QR agenda"
git push origin main
```

Ready for your next feature sprint! 🚀📋