grpc: directory replication API for websites to mirror accounts/channels

Snapshot (full read) + Subscribe (live stream) over the same committed-entry
channel gossip uses. Identity and metadata only — password hashes, SCRAM
verifiers, cert fingerprints, and the finer channel-ops-list events never
cross this API. Bearer-token authenticated, optional server TLS. Verified
end-to-end against a live test-net registration, not just unit tests.

src/engine/db.rs

@@ -236,6 +236,24 @@ impl LogEntry {
     }
 }
 
+// Read-only accessors for consumers outside this module (the gRPC replication
+// layer subscribes to the same broadcast channel gossip does, and translates
+// each entry to a wire message).
+impl LogEntry {
+    pub fn origin(&self) -> &str {
+        &self.origin
+    }
+    pub fn seq(&self) -> u64 {
+        self.seq
+    }
+    pub fn lamport(&self) -> u64 {
+        self.lamport
+    }
+    pub fn event(&self) -> &Event {
+        &self.event
+    }
+}
+
 // Append-only log, the sole persistent source of truth: `open` replays it,
 // `append` stamps and writes a locally-authored entry, and `ingest` folds in an
 // entry authored by another node. The version vector (highest seq applied per
@@ -886,6 +904,11 @@ impl Db {
         self.channels.values()
     }
 
+    /// All registered accounts, for a directory snapshot (see the gRPC layer).
+    pub fn accounts(&self) -> impl Iterator<Item = &Account> {
+        self.accounts.values()
+    }
+
     /// Names of channels founded by `account` (case-insensitive).
     pub fn channels_owned_by(&self, account: &str) -> Vec<String> {
         self.channels

src/engine/mod.rs

@@ -122,6 +122,11 @@ impl Engine {
         self.db.missing_for(peer)
     }
 
+    // A full read of current directory state, for the gRPC Snapshot RPC.
+    pub fn directory_snapshot(&self) -> (Vec<db::Account>, Vec<db::ChannelInfo>) {
+        (self.db.accounts().cloned().collect(), self.db.channels().cloned().collect())
+    }
+
     pub fn gossip_ingest(&mut self, entry: LogEntry) -> std::io::Result<()> {
         // If ingesting a peer's entry removed an account a local session relied on
         // (lost a conflict, or dropped elsewhere), clean up after it.