fix: signer-scoped DirectV1 routing (#162)

Core is no longer account-aware: the client resolves an account address
to signer ids via the account directory, and the signer's verifying-key
hex serves as registry key, inbox subscription, and Welcome routing
target end to end. The MLS credential stays the full id().

- GroupV2 reads the de-mls member id from the fetched key package and
  maps it to the signer id the welcome is delivered to.
- All account machinery (directory trait, bundle codec, resolution)
  moves out of core into logos-account; the RegistrationService
  supertrait and Core::account_directory() are gone, and the client
  holds its own directory handle.
- The account exposes functionality, never a signer: add_delegate_signer
  does the lamport upsert and signs internally.
- Every client acts for an account (ChatClientBuilder::new(account)).
  DelegateSigner is a pure keypair; the client composes the wire
  credential from the signer and the account, so the association is
  client state. addr() is the account address.
- resolve_device_ids fails fast (NotAnAccountKey / NoDeviceBundle /
  Directory) instead of falling back to treating an unresolved address
  as a signer id. LogosChatClient::open and chat-cli mint and publish a
  dev account each launch.
- EphemeralRegistry keys key packages by hex pubkey like HttpRegistry.

Supersedes #155 (routing_id).

core/integration_tests_core/src/lib.rs

@@ -1,4 +1,6 @@
 mod test_client;
+mod test_ident;
 mod wakeup;
 
 pub use test_client::TestHarness;
+pub use test_ident::TestIdent;

core/integration_tests_core/src/test_client.rs

@@ -1,5 +1,5 @@
+use crate::test_ident::TestIdent;
 use libchat::{ConversationId, Core, IdentityProvider, PayloadOutcome};
-use logos_account::TestLogosAccount;
 use shared_traits::IdentId;
 use std::collections::HashMap;
 use std::fmt::Debug;
@@ -21,14 +21,8 @@ const RAYA: usize = 1;
 const PAX: usize = 2;
 const MIRA: usize = 3;
 
-// type ClientType = CoreClient<TestLogosAccount, LocalBroadcaster, EphemeralRegistry, WP, MemStore>;
-type ClientType = Core<(
-    TestLogosAccount,
-    LocalBroadcaster,
-    EphemeralRegistry,
-    WP,
-    MemStore,
-)>;
+// type ClientType = CoreClient<TestIdent, LocalBroadcaster, EphemeralRegistry, WP, MemStore>;
+type ClientType = Core<(TestIdent, LocalBroadcaster, EphemeralRegistry, WP, MemStore)>;
 
 #[derive(Debug)]
 pub struct ReceivedMessage<T> {
@@ -151,7 +145,7 @@ impl<const N: usize> TestHarness<N> {
 
         for i in 0..N {
             let wp = ws.new_provider(i);
-            let ident = TestLogosAccount::new(Self::names(i));
+            let ident = TestIdent::new(Self::names(i));
 
             addresses.insert(i, ident.id().clone());
             let core_client =

core/integration_tests_core/src/test_ident.rs

@@ -0,0 +1,41 @@
+use crypto::{Ed25519SigningKey, Ed25519VerifyingKey};
+use libchat::IdentityProvider;
+use shared_traits::{IdentId, IdentIdRef};
+
+/// Test identity with a fixed, human-readable id ("saro"). Stands in for a
+/// device signer so core tests can address peers by name.
+pub struct TestIdent {
+    id: IdentId,
+    signing_key: Ed25519SigningKey,
+    verifying_key: Ed25519VerifyingKey,
+}
+
+impl TestIdent {
+    pub fn new(explicit_id: impl Into<String>) -> Self {
+        let signing_key = Ed25519SigningKey::generate();
+        let verifying_key = signing_key.verifying_key();
+        Self {
+            id: IdentId::new(explicit_id.into()),
+            signing_key,
+            verifying_key,
+        }
+    }
+}
+
+impl IdentityProvider for TestIdent {
+    fn id(&self) -> IdentIdRef<'_> {
+        &self.id
+    }
+
+    fn display_name(&self) -> String {
+        self.id.to_string()
+    }
+
+    fn public_key(&self) -> &Ed25519VerifyingKey {
+        &self.verifying_key
+    }
+
+    fn sign(&self, payload: &[u8]) -> crypto::Ed25519Signature {
+        self.signing_key.sign(payload)
+    }
+}