feat(core/connection-credentials): add ConnectionCredentials + RemoteIdentity to alknet-core

Phase 0 of crate extraction. Purely additive — adds two small types
(ConnectionCredentials, RemoteIdentity) to a new credentials.rs module
in alknet-core. No other crates touched. All workspace tests pass.

crates/alknet-core/src/credentials.rs

@@ -0,0 +1,91 @@
+//! Transport-level credential bundle for outbound connections (ADR-091).
+//!
+//! `ConnectionCredentials` carries the two dimensions the dial consumes:
+//! the local node's TLS identity and the expected remote identity.
+//! It is transport-agnostic — consumed by `alknet-tls` (TLS setup) and
+//! `alknet-client` (dial).
+
+use crate::config::TlsIdentity;
+
+/// Expected identity of the remote node (ADR-017 §7, extended by ADR-034 §2).
+///
+/// Carries a fingerprint string the assembly layer derives from `Capabilities`
+/// when the local node has a `PeerEntry` for the remote (the known-peer case →
+/// fingerprint pin).
+///
+/// `remote_identity: None` is the **public X.509 endpoint** case: the local
+/// node has no `PeerEntry` for the remote, so there is no fingerprint to pin.
+/// Combined with an X.509 transport, `None` selects CA verification
+/// (`WebPkiServerVerifier`) per the verifier-selection rule in ADR-034 §3.
+/// Combined with an Ed25519 raw-key transport, `None` fails closed (raw-key
+/// remotes are always known peers — no CA to fall back to).
+///
+/// The `Option` is therefore load-bearing, not cosmetic: `Some(fingerprint)`
+/// means "pin this" (known peer), `None` means "trust the CA or fail"
+/// (unknown remote). An implementer must not default `remote_identity` to a
+/// placeholder value to "satisfy" the field — `None` is a real state that
+/// drives verifier selection.
+#[derive(Debug, Clone)]
+pub struct RemoteIdentity {
+    pub fingerprint: String,
+}
+
+/// Credentials for an outbound connection (ADR-091). All dimensions come from
+/// `Capabilities` (ADR-014), never from environment variables — see the
+/// No-Env-Vars Invariant in
+/// `docs/architecture/crates/call/client-and-adapters.md`.
+#[derive(Debug, Clone, Default)]
+pub struct ConnectionCredentials {
+    /// The local node's TLS identity (RFC 7250 raw key or X.509), derived
+    /// from the vault at startup.
+    pub tls_identity: Option<TlsIdentity>,
+    /// Expected fingerprint/cert of the remote node, stored as a capability.
+    /// `Some` → fingerprint pin (known peer with a `PeerEntry`); `None` → CA
+    /// verification for X.509 remotes, fail-closed for Ed25519 raw-key remotes
+    /// (ADR-034 §2/§3). `None` is the public-X.509-endpoint state, not a
+    /// missing field — must not be defaulted to a placeholder.
+    pub remote_identity: Option<RemoteIdentity>,
+}
+
+impl ConnectionCredentials {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn with_tls_identity(mut self, tls_identity: TlsIdentity) -> Self {
+        self.tls_identity = Some(tls_identity);
+        self
+    }
+
+    pub fn with_remote_identity(mut self, remote: RemoteIdentity) -> Self {
+        self.remote_identity = Some(remote);
+        self
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn connection_credentials_builder_methods() {
+        let creds = ConnectionCredentials::new().with_remote_identity(RemoteIdentity {
+            fingerprint: "SHA256:abc".to_string(),
+        });
+        assert_eq!(
+            creds.remote_identity.as_ref().unwrap().fingerprint,
+            "SHA256:abc"
+        );
+        assert!(creds.tls_identity.is_none());
+    }
+
+    #[test]
+    fn connection_credentials_none_is_load_bearing_not_defaulted() {
+        let creds = ConnectionCredentials::new();
+        assert!(
+            creds.remote_identity.is_none(),
+            "ConnectionCredentials::new() must keep remote_identity as None (the load-bearing \
+             public-X.509-endpoint state), not default it to a placeholder"
+        );
+    }
+}

crates/alknet-core/src/lib.rs

@@ -8,6 +8,7 @@
 
 pub mod auth;
 pub mod config;
+pub mod credentials;
 pub mod endpoint;
 pub mod fingerprint;
 pub mod ownership;
@@ -15,5 +16,6 @@ pub mod store;
 pub mod types;
 
 pub use auth::{IdentityProvider, IdentityStore};
+pub use credentials::{ConnectionCredentials, RemoteIdentity};
 pub use ownership::{InMemoryOwnershipStore, OwnershipError, OwnershipProvider, OwnershipStore};
 pub use store::{CredentialStore, EncryptedData, InMemoryCredentialStore, StoreError};