Scaffold Rust workspace: warzone-protocol, server, client, mule

4 crates, all compile. 16/17 tests pass.

warzone-protocol (core crypto):
- Seed-based identity (Ed25519 + X25519 from 32-byte seed via HKDF)
- BIP39 mnemonic encode/decode (24 words)
- Fingerprint type (SHA-256 truncated, displayed as xxxx:xxxx:xxxx:xxxx)
- ChaCha20-Poly1305 AEAD encrypt/decrypt with random nonce
- HKDF-SHA256 key derivation
- Pre-key bundle generation with Ed25519 signatures
- X3DH key exchange (simplified, needs X25519 identity key in bundle)
- Double Ratchet: full implementation with DH ratchet, chain ratchet,
  out-of-order message handling via skipped keys cache
- Message format (WarzoneMessage envelope + RatchetHeader)
- Session type with ratchet state
- Storage trait definitions (PreKeyStore, SessionStore, MessageQueue)

warzone-server (axum):
- sled database (keys, messages, one-time pre-keys)
- Routes: /v1/health, /v1/keys/register, /v1/keys/{fp},
  /v1/messages/send, /v1/messages/poll/{fp}, /v1/messages/{id}/ack

warzone-client (CLI):
- `warzone init` — generate seed, show mnemonic, save to ~/.warzone/
- `warzone recover <words>` — restore from mnemonic
- `warzone info` — show fingerprint and keys
- Seed storage at ~/.warzone/identity.seed (600 perms)
- Stubs for send, recv, chat commands

warzone-mule: Phase 4 placeholder

Known issue: X3DH test fails (initiate/respond use different DH ops
due to missing X25519 identity key in bundle). Fix in next step.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

warzone/crates/warzone-protocol/src/errors.rs

@@ -0,0 +1,34 @@
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum ProtocolError {
+    #[error("invalid seed length")]
+    InvalidSeedLength,
+
+    #[error("invalid mnemonic")]
+    InvalidMnemonic,
+
+    #[error("invalid fingerprint format")]
+    InvalidFingerprint,
+
+    #[error("invalid signature")]
+    InvalidSignature,
+
+    #[error("pre-key signature verification failed")]
+    PreKeySignatureInvalid,
+
+    #[error("X3DH key exchange failed: {0}")]
+    X3DHFailed(String),
+
+    #[error("ratchet error: {0}")]
+    RatchetError(String),
+
+    #[error("decryption failed")]
+    DecryptionFailed,
+
+    #[error("message too old (exceeded max skip)")]
+    MaxSkipExceeded,
+
+    #[error("serialization error: {0}")]
+    SerializationError(String),
+}