v0.0.13: Sender Keys for efficient group encryption

Protocol (sender_keys.rs):
- SenderKey: symmetric key with chain ratchet (forward secrecy per chain)
- generate(), rotate(), encrypt(), decrypt()
- SenderKeyDistribution: share key via 1:1 encrypted channel
- SenderKeyMessage: encrypted group message (O(1) instead of O(N))
- Chain key ratchets forward on each message (HKDF)
- Generation counter for key rotation tracking
- 4 tests: basic, multi-message, rotation, old-key rejection

WireMessage:
- GroupSenderKey variant: encrypted group message
- SenderKeyDistribution variant: key sharing

Server: dedup handles new variants.
CLI TUI + recv: stub handlers for new message types.
23/23 protocol tests pass.

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

warzone/crates/warzone-client/src/cli/recv.rs

@@ -123,6 +123,12 @@ pub async fn run(server_url: &str, identity: &IdentityKeyPair) -> Result<()> {
             Ok(WireMessage::FileChunk { filename, chunk_index, total_chunks, sender_fingerprint, .. }) => {
                 println!("  [file chunk] {} chunk {}/{} of '{}'", sender_fingerprint, chunk_index + 1, total_chunks, filename);
             }
+            Ok(WireMessage::GroupSenderKey { sender_fingerprint, group_name, .. }) => {
+                println!("  [group] {} sent to #{}", sender_fingerprint, group_name);
+            }
+            Ok(WireMessage::SenderKeyDistribution { sender_fingerprint, group_name, .. }) => {
+                println!("  [sender key] received key from {} for #{}", sender_fingerprint, group_name);
+            }
             Err(e) => {
                 eprintln!("  failed to deserialize message: {}", e);
             }

warzone/crates/warzone-client/src/tui/app.rs

@@ -1340,6 +1340,38 @@ fn process_wire_message(
                 // Received chunk without header — ignore
             }
         }
+        WireMessage::GroupSenderKey {
+            id: _,
+            sender_fingerprint,
+            group_name,
+            generation: _,
+            counter: _,
+            ciphertext: _,
+        } => {
+            // TODO: decrypt with stored sender key for this sender+group
+            messages.lock().unwrap().push(ChatLine {
+                sender: sender_fingerprint[..sender_fingerprint.len().min(12)].to_string(),
+                text: format!("[group #{} sender-key message — key setup needed]", group_name),
+                is_system: false,
+                is_self: false,
+                message_id: None,
+            });
+        }
+        WireMessage::SenderKeyDistribution {
+            sender_fingerprint,
+            group_name,
+            chain_key: _,
+            generation: _,
+        } => {
+            // TODO: store this sender key for future group decryption
+            messages.lock().unwrap().push(ChatLine {
+                sender: "system".into(),
+                text: format!("Received sender key from {} for #{}", &sender_fingerprint[..sender_fingerprint.len().min(12)], group_name),
+                is_system: true,
+                is_self: false,
+                message_id: None,
+            });
+        }
     }
 }