crypto_negotiation module enables transitioning between crypto modes:
GroupCryptoState tracks current mode:
- MlsLite (signed/unsigned)
- FullMls (classical/hybrid)
- Upgrading (transition state)
MlsLiteBootstrap derives MLS-Lite keys from MLS epoch secret:
- Enables fallback to MLS-Lite over constrained links
- Same group can use full MLS over WiFi, MLS-Lite over LoRa
Upgrade protocol:
1. Member sends KeyPackage over fast link
2. Creator creates MLS Welcome
3. Group transitions to full MLS
4. Optionally maintains MLS-Lite fallback for constrained links
